Phylum Mollusca, characteristics, phylum Mollusca examples, function, types, MCQ, Terminal question,

Phylum Mollusca 

Phylum Mollusca (L., molluscus, soft) includes soft-bodied invertebrate animals such as Octopods, snails, slugs, mussels, clams, oysters, tusk-shells, squids etc. The term Mollusca were coined by Johnston. It is a diverse and widespread group, with about 112,000 species. Molluscs are the largest marine phylum, comprising about 23% of all the named marine organisms. Molluscs may be terrestrial or aquatic (freshwater or marine). They are found in all habitats - deserts, forests, lakes, rivers, abysses of sea, coral reefs, underground or even as parasite in the body of other animals.

They may be found clinging to the rocks, crawling, and swimming, burrowing or even digging. They have diversified feeding habit and can be herbivores, carnivores or omnivores. They vary in size from giant squids (nearly 2m long) to little snails, a millimeter long. The largest of the molluscan classes is Gastropods, which is represented by about 35,000 living and some 15,000 fossil species.

The three most universal features defining molluscs are - a mantle with a significant cavity used for 

breathing and excretion, the presence of a radula, and the structure of the nervous system. The "generalized" mollusc's feeding system consists of a rasping "tongue", the radula, and a complex digestive system. Although molluscs are coelomates, the coelom tends to be small, and the main body cavity is a hemocoel through which blood circulates; their circulatory systems are mainly open. The generalized Mollusca has two paired nerve cords, or three in bivalves. Most molluscs have eyes, and all have sensors to detect chemicals, vibrations, and touch. The simplest type of molluscan reproductive system relies on external fertilization, but more complex variations occur. All produce eggs, from which may emerge trochophore larvae, more complex veliger larvae, or miniature adults Molluscan shells have always been economically important, having served as money in early days. They have been used in jewellery and buttons. Octopus, Scallops, oysters and squids are important food items. The scientific study of molluscs is called malacology.

Habit and Habitat: -

✔Mollusca's family occur in almost in every condition every habitat found in earth, they are most conspicuous organisms.

✔Some of them found in the marine environment and some is in freshwater as well as terrestrial habitats.

✔Marine Mollusca occur on a large variety of substrates including rocks, coral reefs, mud flats, and sandy beaches. 

✔The adoption of different feeding habitat appears to have had a profound influence on molluscan evolution.

✔The change from grazing to other forms of food acquisition is one of the major features in the evolutionary of the group.

✔Truly herbivorous grazers are relatively rare and are limited to some polyplacophorans and a few gastropods groups.

General characters: - 

• Molluscs are essentially aquatic, mostly marine, few freshwaters and some terrestrial animals. 
• Body is soft, bilaterally symmetrical, unsegmented and without jointed appendages. 
• Body can be divided into head, mantle, visceral mass and foot. 
• Body is commonly protected by an exoskeletal calcareous shell of one or more pieces, secreted by the mantle. 
• The head carries mouth, eyes and tentacles. 
• The mantle is a thick, muscular fold of body wall extended over the viscera and thus enclosing a space, the mantle cavity. 
• Visceral mass contains the visceral organs of the body in a compact form.
• The foot is ventral in position and is usually thick and muscular being variously modified for creeping, ploughing and seizing but is absent in oysters.
• Body cavity is haemocoel. The true coelom is generally limited to the pericardial cavity and the lumen of the gonads and nephridia. 
• Digestive system is complete. Digestive glands are liver or hepatopancreas. Radula is mostly present. 
• Circulatory system is closed type. Heart has one or two auricles and one ventricle. 
• Respiration direct or by gills or lungs or both. The respiratory pigment is hemocyanin. 
• Excretion is performed by nephridia or kidneys. 
• Nervous system consists of paired cerebral, pleural, pedal and visceral ganglia joined by longitudinal and transverse connectives and nerves.
• Sexes are separating (dioecious) but some are hermaphrodite. Fertilization happens externally as well as internally. 
• Development is either direct or with metamorphosis through the trochophore stage called veliger larva. 

SOME EXAMPLES OF MOLLUSCA: - 

1. Octopus: -

 An Octopus (Commonly called devil fish) is a cephalopod Mollusca of the order Octopoda. This nocturnal marine creature inhabits many diverse regions of the ocean, including coral reefs, pelagic waters and the ocean floor. It is generally found on the Pacific and Atlantic coasts. Around 300 species are recognized, which is over one-third of the total number of known cephalopod species. Octopuses are among the most intelligent and behaviorally flexible of all invertebrates. Humans in many cultures eat Octopus. 

The body is unsegmented, symmetrical and soft bodied animals. Variations can be found in body parts based on species and/or geography. The head bears a pair of eyes. The mouth is surrounded by eight elongated equal arms webbed at the base and each arm bears suckers arranged in two rows. Octopus crawls on the ground and is able to change its color according to the background. The food is captured by the arms and is broken by radula and a pair of jaws. Octopus ejects ink from the ink-gland into the surrounding water, producing a smoky cloud. In males one of the arms, called hectocotylized arm, bears a spoon shaped organ at its end. The arm is used to caress the female and deposit spermatophores beneath its mantle. Sexes are separate. Development is direct. There is no larval stage. It feed upon crabs, bivalves and fishes etc.2. Sepia: -

 Sepia (Commonly known as cuttle fish) is an invertebrate belonging to the Phylum Mollusca. It is a marine animal that occupies shallow to mid water and is often associated with coral reefs. Body is 

unsegmented, bilaterally symmetrical and soft and is divisible into a large head, a small neck or collar and trunk. The head is well developed, bears a pair of eyes and 10 oral arms which are a modification of foot. Eight oral arms are smaller while two are longer and are called tentacles. The trunk extends into flaps called lateral fins on either side that help the animal in swimming. It is covered by a thick muscular mantle, enclosing a large mantle cavity, on the ventral side which contains viscera. The Sexes are separate, and reproduction is sexual. It is nocturnal and carnivorous.

3. Doris: -

 Doris (Commonly known as sea-lemon) is a sluggish marine animal found under stones at low tide marks. Head bears a pair of short retractile olfactory tentacles called rhinophores. Mantle is usually pigmented and contains calcareous spicules and tubercles. Mouth is present on ventral side. Foot is ventral with a broad sole for creeping. The body is bilaterally symmetrical, unsegmented, flat, short 

and oval with convex dorsal surface. The animal is bisexual; the penis and the genital aperture lie 

asymmetrically on the right side. The anus lies mid-dorsally near the posterior end and is surrounded by a circlet of feathery, retractile secondary gills, called cerata. Development includes a free-swimming

veliger larva.

4. Chiton: -

Chitons (formerly known as Amphineura) are marine molluscs which belong to class Amphineura and subclass Polyplacophora (fig. 4). Their size varies from small to large. About 940 extinct and 430 fossil species are recognized. Chiton is commonly known as sea-mice. Chitons are mainly found in shallow water, often under rocks and other shells, but several genera can be found in water as deep as 5,000 ft. Some are actively carnivorous, feeding on small crustaceans by smothering them with the girdle, e.g., Lepidochitona. They become active at twilight and move around very slowly in search of food. Most are grazers, and with a multi-toothed radula, they can feed on small algae and other tiny organisms.

Body is unsegmented, bilaterally symmetrical and Dorso-ventrally compressed. It consists of shell, foot, mantle and visceral mass. Shell is calcareous and is present on the dorsal side and is composed 

of 8 overlapping plates. Head is not distinct. Eyes and tentacles are absent. Foot is ventral, broad, 

sole-like and muscular, adapted for creeping and adhering. Mantle covers greater part of body and 

partly covers the edges of the shell plates. Mouth and anus are at opposite ends. Gills lie along whole length of mantle groove. Sexes are separate, gonad is single and median. Fertilization is external. Development is indirect through trochophore larva. 

5. Pecten: -

Pecten (Commonly known as scallop) is a free-swimming marine molluscs that lives on sea bottom of 10 fathoms deep. Shell is beautifully ribbed by radiating lines. The two shell valves are unequal, the right being larger and more convex and the animal rests on this valve. Locomotion takes place in spurts; the swimming is affected by the rapid opening and closing of shell valves. Foot is very much reduced. Two large gills are present. Pectens are bisexual. It is found mainly in U.S.A. and India.

6. Loligo: -

 Loligo is commonly called sea squid and is found all over the world in shallow to mid waters. Body is spindle or torpedo-shaped and divisible into head, foot and visceral hump. The head is well developed, bears a pair of eyes and ten oral arms which are a modification of foot. Eight oral arms are smaller while two are longer and are called tentacles. Shell is internal and cartilaginous. Two nephridia or 

kidneys are also present. Sexes are separate. An ink sac is present and serves for defence. Loligo is used as food by Chinese and Italians and also as bait for marine fishing.

7. Dentalium: -

 Dentalium (Commonly known as tusk shell) is a marine mollusc found world over in the sublittoral zone of seas. It measures 2-5 cm in length. It lies in a tubular, bilaterally symmetrical shell open at both ends. Head and foot project out from the anterior aperture of the shell. Head bears a mouth surrounded

by filiform tentacles called captacula. Eyes and osphradium are absent. Mantle is entirely within the shell. The foot is long pointed, spade-like and highly extensible adapted for digging and burrowing (Rastogi). Sexes are separate. Development is indirect and includes a trochophore larva. Shell of Dentalium is used for ornamental purposes. Its shells were once used by Red Indians of America as currency. It feeds on microorganisms like diatoms and foraminifera.

8. Unio: -

 Unio is commonly known as freshwater mussel. Freshwater mussels are found in freshwater lakes, rivers and streams, inhabiting the surface layers of the muddy beds of rivers and lakes. It crawls slowly with the help of its plough-like, wedge-shaped muscular foot that leaves a deep trail all along its journey. It usually moves to shallow places by night and retires to deeper places by day. Food consists of microscopic organisms, both animals and plants, which are fed upon by filter-feeding mechanism involving both ciliary as well as mucoid movements. Animal responds to light, touch or some other stimulus by withdrawing its foot and closing the siphons, meant for incoming and outgoing water currents. Soft-bodied animal is completely enclosed within a calcareous shell which represents its exoskeleton. Unio is dioecious, i.e. the sexes are separate, but there is no external dimorphism.

8. Aplysia: -

Aplysia is commonly known as sea-hare. It is a marine animal found in tropical waters. It is found in India, West Indies and on the Florida Coast. It crawls over the surface of rocks and boulders. The body is soft and lumpy with a thin flexible plate-like shell covered by mantle. The head has two pairs of tentacles. The posterior pair tentacles become ear-like and are called rhinophores. The foot is broad and flat and bears a pair of lateral folds parapodia that help in swimming. Mantle possesses unicellular ink glands. These secrete purple ink used for defense. It is bisexual. It has a single gonoduct. Aplysia is known to form mating chains with up to 20 animals. The eggs are yellow-green, and change after 8 to 9 days into a brown color before larvae hatch. The life span is assumed to be around a year. Cooler temperature delays spawning and has been shown to extend the lifespan. Sea hare is hermaphroditic, acting as male and female simultaneously during mating. Aplysia is herbivorous. Its diet consists primarily of red algae like Procambium pacificism, Ceramium eatonianum and Laurencia Pacifica which gives the animal its typically reddish or pinkish coloration. Thus Aplysia resembles the food it grazes on and cannot be distinguished easily from the seaweed unless the animal is moving.

9. Eolis: -

Eolis (Commonly known as sea slug) is a marine slug-like gastropod found in shallow waters crawling under surface of seaweeds. It is a small neudibranch 1 or 2 cm in length. Head bears two pair of cylindrical retractile tentacles and sessile eyes at the base of the posterior pair of tentacles. The mouth is prominent and can be most easily seen from the ventral view. Foot is muscular and ventral and serves for locomotion. Shell, mantle and true gills are absent. It is hermaphroditic and common gonad is protrandric. The animal is said to feed on hydroids which are digested and their undischarged nematocysts are collected in the cerata and discharged on irritation.

Important point: -

• Phylum mollusca (L., molluscus, soft) includes soft-bodied invertebrate animals such as Octopods, snails, slugs, mussels, clams, oysters, tusk-shells, squids etc. It is a very successful, diverse and widespread group, with about 112,000 species. 
• The largest of the molluscan classes is Gastropoda, which is represented by about 35,000 living and some 15,000 fossil species. 
• Molluscs can be segregated into seven classes: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and Scaphopoda. These classes are distinguished by, among other criteria, the presence and types of shells they possess. 
• Class Aplacophora includes worm-like animals with no shell and a rudimentary body structure. Members of class Monoplacophora have a single shell that encloses the body. 
• Members of class Polyplacophora are better known as "chitons;" these molluscs have a large foot on the ventral side and a shell composed of eight hard plates on the dorsal side. 
• Class Bivalvia consists of mollusks with two shells held together by a muscle; these include oysters, clams, and mussels. 
• Members of class Gastropoda have an asymmetrical body plan and usually have a shell, which can be planospiral or conispiral. Their key characteristic is the torsion around the perpendicular axis on the center of the foot that is modified for crawling. 
• Class Scaphopoda consists of mollusks with a single conical shell through which the head protrudes, and a foot modified into tentacles known as captaculae that are used to catch and manipulate prey.
• Molluscan shells have always been economically important, having served as money in early days. They have been used in jewellery and buttons. The scientific study of molluscs is called malacology. 
• Pila globosa is one of the largest freshwater molluscs that have invaded various kinds of habitats. It is commonly found in ponds, lakes, tanks, pools, marshes, paddy fields, streams and rivers of Northern India. The shell of Pila, as in other Gastropoda is univalve but coiled around a central axis in a right-handed spiral. It comprises of following three layers, periostracum, ostracum and hypostracum. 
• Body of Pila is divisible into four regions head, foot, visceral mass and mantle. Head is the anterior fleshy part of the body overhanging the foot. It bears mouth, two pairs of contractile tentacles and a pair of eyes. Foot is the locomotory organ of Pila and lies below the head. All visceral organs are contained in this lump like structure that lies above the head-foot complex. Skin of the visceral mass forms a thin and delicate covering called the mantle.
• The nervous system is well developed and comprises of two main parts – Central Nervous System and Peripheral Nervous System. Central Nervous System consists of ganglia and their commissures (connections between similar ganglia) and connectives (connections between dissimilar ganglia). The peripheral nervous system consists of nerves arising from CNS and innervates various parts of the body. 
• The sexes are separate in Pila and sexual dimorphism is distinct. The shell of the female is larger and more globular than that of the male. The copulatory organs or penis is well developed in male but poorly developed in female. 
• The male reproductive system consists of testis, vasa efferentia, vas deferens, copulatory organs and hypobranchinal gland. The female reproductive system consists of ovary, oviduct, receptaculum seminis, uterus, vagina, copulatory organ and hypobranchial gland. 
• Fertilization is internal but the development of the embryo takes place outside the body of female. Female lays 200-800 eggs at a time in moist earth in a sheltered cavity near ponds and lakes. The eggs are rounded and as big as the pea seeds. 
• During development, due to torsion, the visceral mass and the shell of embryo become spirally coiled. A young snail emerges from the fertilized egg. The young ones resemble the adult in form

Fill in the blanks: - 

1. Pila is popularly known as…….. 
2. Mode of respiration of Pila is ………….and……….. 
3. The study of molluscs is generally known as………… 
4. Pearl is secreted by………. 
5. Respiratory pigment in mollusca is……….

Answer:-  1). Apple snail 2). Aquatic and aerial 3). Malacology 4). Mantle 5). Haemocyanin

Multiple choice questions:- 

1. Excretory organ of Pila is: - 

(a) Kidney                                   (b) Keber’s organ 

(c) Renal organ                          (d) none 

2. The Pila is: - 

(a) Undifferentiated             (b) Hermaphrodite 

(c) Monoecious                   (d) Dioecious 

3. Aerial respiration in Pila occurs from:-

(a) Ctenidium                       (b) Pulmonary sac 

(c) Mantle                             (d) Branchiae 

4. Torsion is shown in:- 

(a) Pila                                   (b) Loligo 

(c) Unio                                 (d) Mytilus 

5. Identify the larva which is characteristic of Gastropoda and Scaphopoda: 

(a) Muller’s larva                 (b) Trochophore larva 

(c) Veliger larva                    (d) Bipinnaria larva 

6. The freshwater clam or mussel is: 

(a) Mytilus                            (b) Ensis 

(c) Anodonta                        (d) Pholas 

7. Ctenidium performs respiration is: 

(a) Air                                   (b) Water 

(c) Both the place                (d) Terrestrial 

8. Which one is a connecting link between Annelida and Mollusca? 

(a) Chaetoderma                (b) Nautilus 

(c) Neopilina                       (d) Lymnaea 

9. Concology is the study of: 

(a) Mollusca                       (b) Shell of mollusca 

(c) Foot of mollusca          (d) Behaviour of mollusca 

10. The larva of mollusca: 

(a) Glochidium                  (b) Veliger 

(c) Both                              (d) None 

Answer Key :- 

1.) c 2) d 3) b 4) a 5) b 6) c 7) b  8) c 9) b 10) c

Self Assessment Question: -

1. Classify Pila upto order? 

2. Describe the morphology of the shell of Pila? 

3. Discuss the nervous system of Pila? 

4. Describe the reproductive organs of Pila?

5.What are some representatives of the phylum Mollusca? 

6. In which habitats do molluscs live? 

7. What is the morphological feature of molluscs after which the phylum is named? 

8. What are examples of the ecological and economic importance of molluscs? 

Phylum Arthropoda, characters of Arthropoda, function, classification, example, top question,

 Phylum Arthropoda

Phylum Arthropoda (Gr., arthros = joint + podos = foot) is the largest phylum and most varied in the animal kingdom. Von Siebold gave the name Arthropoda. It includes well over one million described species and many million remain unstudied. Some of the more well-known arthropods include insects, crustaceans, spiders, scorpion and centipede as well as the fossil trilobites. Arthropods are mainly terrestrial but marine and freshwater species are also well known. Arthropoda varies tremendously in their habitats, life histories, and dietary preferences.

Arthropod bodies are divided into segments. However, a number of segments are sometimes fused to form integrated body parts known as tagmata. This process of fusion is called tagmosis. The head, thorax, and abdomen are examples of tagmata. Exoskeleton serves as protection and provides places for muscle attachment. Arthropods must molt because their exoskeletons don’t grow with them. However, in most species some appendages have been modified to form other structures, such as mouthparts, antennae, or reproductive organs. Arthropod appendages may be either biramous (branched) or uniramous (unbranched). In insects, the anterior portion of the heart is extended into atube that is called an aorta which directs the blood forward as it goes out into the body cavity. Arthropods have a well-developed, mesodermal, solid nerve cord, ventral and well-developed sense organs. They range in size from microscopic plankton to life-forms that are a few meters long. Arthropods primary internal cavity is known as hemocoel, which accommodates their internal organs, and through which their hemolymph - analogue of blood - circulates; they have open circulatory systems.

Respiration occurs in various ways for e.g. some species have gills, while others employ tracheae, or book lungs. The tracheal respiratory system consists of external openings called spiracles that are linked to a system of branched tubules which allow respiratory gases to reach internal tissues. Arthropods are characterized by a brain as well as a nerve ring around the area of the pharynx, in theoral cavity. A double nerve cord extends backwards along the ventral surface of the body, and each body segment is associated with its own ganglion, or mass of nerve cells. Generally, the sexes areseparate in phylum Arthropoda. Fertilization usually occurs internally, and most species are egg laying. While some species exhibit direct development, in which eggs hatch as miniature versions of adults, other species pass through an immature larval stage and undergo a dramatic metamorphosis before reaching adult form. Arthropods contribute directly (as food) as well as indirectly (crop pollination) to human food supply chain. Some specific species are known to spread severe disease to humans, livestock, and crops.

GENERAL CHARACTERS: -

• Arthropoda is bilaterally symmetrical, triploblastic and metamerically segmented animals. 
• Body can be divided into head, thorax and abdomen; head and thorax are often fused to form Cephalothorax. 
• Body is covered with a thick chitinous cuticle forming an exoskeleton. 
• Body segments usually bear paired and jointed appendages. 
• Coelom largely a blood-filled haemocoel. 
• Muscles are mostly striated, usually capable of rapid contraction. 
• Digestive tract is complete. The mouth and anus lie at opposite ends of the body. 
• Circulatory system is open with dorsal heart and arteries and blood sinuses. 
• Respiration through by general body surface, by gills in aquatic forms, by tracheae and by book lungs. 
• Nervous system has dorsal nerve ring. 
• Excretory organs are Malpighian tubules (in insects) and green glands (in Crabs and prawn). 
• Cilia are absent from all parts of the body. 
• Sexes are generally separate. 
• Fertilization is internal, oviparous and ovoviviparous. 
• Parental care is well marked in many arthropods. 

Other types of Arthropoda: - 

1. Limulus: -

Limulus or king crab belongs to the subclass xiphosure and class Merostomata of subphylum Chelicerata. It is a large-sized marine animal, up to 60 cm long. It lives in shallow waters partly buried in the bottom mud. It feeds on worms, algae and mollusks. It is bilaterally symmetrical, triploblastic metamerically segmented animal with jointed appendages. The body is differentiated into prosoma and hinged opisthosoma. Prosoma bears a pair of 3-jointed chelicerae and 5 pairs of 6-jointed legs. First four legs are chelated; fifth is non-chelate. The 7th pair of appendages, chilaria are degenerate and of doubtful functions. (Yadav and Varshney, 2015). The broad hexagonal opisthosoma is divisible into an anterior 6-segmented mesosoma and a posterior 3 segmented metasoma. Excretion takes place through 4 pair of coxal glands. Sexes are separate. In breeding season males and females copulate in shallow water. Eggs, laid by females in holes in sand, are fertilized by sperms. Limulus is found along the eastern coastline of Asia and North America (Kotpal, 2005). 

2. Aranea: -

Aranea belong to the order Araneae of class Arachnida. Body can be divided into prosoma and opisthosoma. Prosoma is covered by carapace that bears 8 simple eyes anteriorly. Ventrally prosoma bears 6 pair of appendages, a pair of chelicerae, a pair of pedipalps and 4 pair of walking legs. Opisthosoma bears spinnerets or spinning organs just anterior to the terminal anus. Respiration happens via book lungs or tracheae or both. Excretory organs are Malpighian tubules. The silk secreted by most spiders is used for construction of egg sacs and for constructing webs to trap insects, as well as a guideline for males in finding sexual partners.

3. Daphnia: -

 Daphnia, also called "water fleas", are found in order Cladocera of subclass branchiopod and are sometimes called cladocerans. Body is about 2 mm long, oval, laterally flattened with a ventral beak on head and a sharp posterior caudal spine. Daphnia has a single compound eye and there are normally five or six appendages attached to the thorax. The body is compressed and enclosed in a flattened, transparent carapace. Antennules are much reduced and uniramous. Daphnia moves by beating its antennae which are moved by large muscles. They feed on algae, protozoa, bacteria, and decaying organic material. Most are filter feeders that consume phytoplankton which they remove from water using their setose thoracic appendages. A few are carnivores preying on other cladocerans. Daphnia swims by rapid jerks of its two large biramous antennae.

4. Cyclops: -

 The Cyclops is named after one-eyed monster of Greek legend. Cyclops is crustacean invertebrate with a hard outer shell. It is the most familiar copepod crustacean found in freshwater ponds. Pear-shaped or elongated body measures 1.5 to 5 mm in length. Head and first thoracic segment become fused to form cephalothorax, which is covered dorsally by a carapace. The cyclops has 5 pair of legs and a divided tail-like appendage called a Furca. It is greenish, straw yellow, or grayish in color. It goes jerking through the water usually in very large numbers. The females carry the eggs in little side sacs and they multiply rapidly. The Cyclops is often seen near water fleas or Daphnia. Many water animals feed upon the Cyclops. It has a very important role in the food chain. Cyclops serves as intermediate hosts for the guineaworm of man.

5. Lepas: -

 Lepas is commonly known as “ship or goose barnacle”. It is a marine animal that inhabits warmer seas. It is found attached to ships and vegetation with the help of peduncle. Lepas is bilaterally symmetrical, triploblastic metamerically
segmented animal with jointed appendages. The body is covered by a thick chitinous exoskeleton and by 5 calcareous plates-a pair of scuta, a pair of terga and a median dorsal carina. They feed upon minute organisms gathered from water and kicked into mouth by the thread like feet. It is bisexual. Development includes a free-swimming cypris larva (Yadav and Varshney, 2015). 

6. Sacculina: -

Sacculina is commonly known as root-headed barnacle. The adult looks like a large tumor or ovoid sax fastened to the abdomen of crab by a short stalk. Appendages, segmentation, sense organs and alimentary canal etc. are absent. The body is made up of two parts- a thin sac present on the ventral abdomen of the host crab and a peduncle. The female sacculina infects a crab. The male sacculina lives within the body of the female and fertilize its eggs. Larva is cirripede-nauplius.

7. Squilla: -

 Squilla is a large marine crustacean and belongs to order stomatopod of subclass malacostraca. Squilla is active, predatory and nocturnal; it catches hold of the prey with powerful maxillipedes. It is found in burrows in the sand or mud at the bottom of the sea. Body is bilaterally symmetrical, metamerically segmented, triploblastic, Dorso-ventrally flattened and 25 cm long. Body is divisible into cephalic, thoracic and abdominal parts. Head bears a pair of stalked movable compound eyes, antennules and antennae. The thoracic region bears 5 pairs of maxillipedes and 3 pairs of walking legs. The second pair of maxillipedes is exceptionally large. The large abdomen is made up of 6 segments and each segment bears a pair of biramous pleopods. The last pair of pleopods are called uropod. It feeds on small fishes, crustaceans, molluscs etc.

8. Eupagurus: -

Eupagurus is commonly known as ‘hermit crab’. It is found inhabiting the empty shells of gastropods. It leads a commensal life. Cephalothorax is broad and flattened. Head bears a pair of stalked elongated eyes, a pair of large antennae and a pair of short antennules. Thorax bears 5 pair of legs. First, fourth and fifth pair of legs are chelated whereas rest of the legs are non-chelate (Verma, 2015). Abdomen appendages of the left side are reduced while those of the right side are absent. Eupagarus is a peculiar crustacean having extreme modifications in order to adjust in the coils of molluscan shells.

9. Cancer: -

Cancer is commonly called rock crab or true crab. Body is Dorso-ventrally compressed and consists of a cephalothorax and an abdomen. Cephalothorax is broader than long and is covered by a carapace. It bears small antennules, antennae, maxillipedes, compound eyes and thoracic legs. Mouth parts present on the ventral surface are covered by the flat, plate-like third maxillipedes. Fifth pairs of thoracic legs are present. The first pair is chelate whereas the remaining are non-chelate. The eggs are carried about by the female attached to abdominal legs (Verma, 2015). Development is indirect through zoea and megalopa larval stages.

10. Gryllus: -

Gryllus belong to the order Orthoptera. Gryllus is the common house cricket which lives in damp warm places like under logs, boxes, and stones and in holes behind boods and crevices and in the kitchens. The body can be divided into head, thorax and abdomen. Head bears a pair of compound eyes and a pair of antennae which are filiform and longer than the body. Mouth parts are mandibulate and well developed. Female possess a well-developed oviposterior that serves for depositing eggs in holes or crevices, devours all sorts of animal and vegetable matter such as clothing paper, skin, fruits and vegetables etc.

11. Mantis: -

 Mantis is commonly called praying mantis. The colour of Mantis is usually green. It is a large insect (5-10cm), with a small triangular head, a long prothorax and abdomen consisting of10-segments. Wings are folded flat and overlap the sides of the body. It is found in areas of green vegetation. It feed voraciously on other insects. Female eats up the male after copulation. The female lays about 200 eggs in frothy mass which soon hardens into a waterproof egg case. 

12. Carausius: -

Carausius is commonly known as stick insect because it mimics a twig to escape enemies. Carausius is herbivorous and is found in tropical forests in thick vegetation. Body is elongated and slender and can be divided into head, thorax and abdomen. Head is small, bears a pair of antennae and a pair of small compound eyes. Thorax is elongated bearing pairs of long slender legs. Abdomen has 10 segments. Mouthparts are of chewing type. Sexes are separate. While male is small, winged and active, the female is large, sluggish and apterous.

Important Point

• Phylum arthropoda (Gr., arthros = joint + podos = foot) is the largest phylum and most varied in the animal kingdom. Arthropods are mainly terrestrial but marine and freshwater species are also well known. Arthropod bodies are divided into segments. 
• A number of segments are sometimes fused to form integrated body parts known as tagmata. This process of fusion is called tagmosis. The head, thorax, and abdomen are examples of tagmata. However, in most species some appendages have been modified to form other structures, such as mouthparts, antennae, or reproductive organs. Arthropod appendages may be either biramous (branched) or uniramous (unbranched). 
• Arthropods have a well-developed, mesodermal, solid nerve cord, ventral and well-developed sense organs. They range in size from microscopic plankton to life-forms that are a few meter long. Arthropods primary internal cavity is known as hemocoel. 
• Respiration occurs in various ways for e.g. some species have gills, while others employ tracheae, or book lungs. Generally, the sexes are separate in phylum arthropoda. 
• Fertilization usually occurs internally, and most species are egg laying. While some species exhibit direct development, in which eggs hatch as miniature versions of adults, other species pass through an immature larval stage and undergo a dramatic metamorphosis before reaching adult form. Some specific species are known to spread severe disease to humans, livestock, and crops.
• Palaemon is commonly known as prawn. It is found in freshwater streams, ditches, lakes, ponds, rivers and reservoirs. It is a nocturnal animal hiding at the bottom during the day and coming to the surface at night in search of food. 

Objective Question of Phylum Arthropoda:-

(1) Metamerically segmented, bilaterally symmetrical animals bearing jointed appendages. These are characteristics of: 

(a) Annilida        (b) Helminths   (c) Arthropoda   (d) Mollusca

(2) An animal without economic importance is: 

(a) Honeybee    (b) Pheritma     (c) Peripatus    (d) Parasite 

(3) Peripatus is connecting link between: 

(a) Annelida and Platyhelminthes      (b) Annelida and Mollusca     (c) Annelida and Arthropoda (d) Mollusca and Arthropoda 

(4) Peripatus is: 

(a) Herbivorous     (b) Carnivorous     (c) Omnivorous     (d) Parasite

 (5) The excretory structure in Peripatus are: 

(a) Nephridia (b) Malpighian tubules (c) Coxal glands (d) Solenocytes

(6) Biting and chewing type of mouth parts occurs in:

(a) Grasshopper  (b) Cockroarch  (c) Cricket  (d) All 

(7) Respiratory organs of crustaceans are: 

(a) Gills (b) Lungs (c) General surface (d) both gills and general surface 

(8) Means of respiration in insects: 

(a) Integuments (b) Blood gills (c) Tracheal gills (d) Spiracular gills (e) All 

(9) The mouth parts of housefly are: 

(a)Biting and chewing type (b) Sucking and sponging type (c) Biting, sucking and lapping type (d) Piercing and sucking type 

(10) Rearing of silkworm is known as: 

(a) Aquaculture (b) Floriculture (c) Sericulture (d) Apiculture 

💥Answer key :-

 (1) c (2) c (3) c (4) a (5) c (6) d (7) a (8) e (9) b (10) c 

💥Terminal Question For external Examination:-

1. To describe the classification of Arthropoda? 

2. What is the economic importance of social insects? 

3. What is the zoological importance of Peripatus? 

4. Describe the mouth parts of insects? 

5. Discuss the reproduction of Palaemon? 

6. Write about the nervous system of Palaemon?

phylum Annelida, Characters of Annelida, Types of Annelida, Lumbricus, Question of phylum Annelida,

 Phylum Annelida

Name of phylum Annelida was first coined by Lamarck (1801) for the higher segmented worms (Gr., annulus - little ring + eidos - form). Annelids are elongated, bilaterally symmetrical and highly organized animals, in which the organs have grouped into definite systems. Appearance of metamerism represents their greatest advancement, so that they are called segmented worms in order to distinguish them from flatworms (Platyhelminthes) and roundworms (Nematodes) which are not segmented. Their paired appendages, when present, are never jointed. Their coelom, nephridia and cephalization are better developed than those of the un-segmented worms. They are the first animals to have a closed vascular system. Nervous system is fundamentally similar to that of Arthropoda and embryology is not much different from that of Mollusca. 

General Characters of Annelida: - 

• Mostly aquatic, some terrestrial. 
• Burrowing or tubicolous. 
• Some commensal and parasitic. 
• Body elongated, bilaterally symmetrical, triploblastic, truly coelomate and meteorically segmented into similar metamers. 
• Epidermis of a single layer of columnar epithelial cells, covered externally by a thin cuticle. 
• Body wall dermo muscular.
• Outer muscle fibers circular, longitudinal. 
• Locomotory organs are segmentally repeated chitinous bristles, called setae or chaetae, embedded in skin. May be borne by lateral fleshy appendages or parapodia. 
• Coelom, true, schizocoelous. Mostly well-developed except in leeches. 
• Usually divided into compartments by transverse septa. 
• Coelomic fluid with cells or corpuscles. 
• Digestive system straight and complete. 
• Digestion entirely extracellular. 
• Blood vascular system is closed.
• Respiratory pigments either hemoglobin or erythrocruorin dissolved in blood plasma. 
• Respiration by moist skin or gills of parapodia and head. 
• Excretory system consisting of metamerically disposed coiled tubes, called nephridia. 
• Nervous system with a pair of cerebral ganglia (brain) and a double ventral nerve cord bearing ganglia and lateral nerves in each segment.
• Sensory organs include tactile organs, taste buds, statocysts, photoreceptor cells and sometimes eyes with lenses in some.
• Hermaphroditic or sexes separate, cleavage pattern spiral and determinate. 
• Larva, when present, is a trochophore. 
• Regeneration is common. 

Classification of Annelida: -

Modern classification of phylum Annelida was proposed by Fauchold (1977) and Parker (1980). About 8,700 known species of annelid are divided into four main classes, primarily on the basis of the presence or absence of parapodia, setae, metamers, and other morphological features. 

A. Class – Polychaeta (Gr., poly- many + chaite- hair) 

• Chiefly marine, some in fresh water. 
• Segmentation internal and external. 
• Head distinct with eyes, palps and tentacles. 
• Setae numerous, on lateral parapodia. 
• Clitellum absent. 
• Sexes separate. 
• Gonads temporary and in many segments. 
• Trochophore larva present. 

Polychaetes are divided into two subclasses, Erranitia and Sedentaria (Fauvel, 1959). However, according to Dab (1963), this subdivision is artificial and not a natural one.

1. Subclass – Erranitia

• Free-swimming, crawling, burrowing or tube-dwelling and predatory polychaetes. 
• Segments numerous and similar, except for head and anal region. 
• Prostomium distinct with sensory structures
• Parapodia with acicula and compound setae. 
• Pharynx protrusible, enlarged and usually with jaws and teeth. 
• Examples: Aphrodite (sea mouse), Polynoe, Phyllodoce, Tomopteris, Syllis, Nereis, Gycera, Eunice, Diopatra, Histriobdella. 

2. Subclass - Sedentaria 

• Sedentary polychaetes living in burrows or tubes. 
• Body made of two or more regions, with dissimilar segments and parapodia. 
• Prostomium small. 
• No acicula and compound setae. 
• Pharynx without jaws and teeth. 

Examples: Chaetopterus, Arenicola, Owenia, Sabella, Sabellaria, Terebella, Amphitrite, Pomatoceros, Spirorbis, Serpula.

2. Class - Oligochaeta (Gr., oligos- few + chaite- hair) 

• Mostly terrestrial, some in fresh water. 
• Segmentation internal and external. 
• Head distinct, without sensory organs. 
• Setae few, embedded in skin. 
• Parapodia absent. 
• Glandular clitellum present for cocoon formation. 
• Hermaphroditic. 
• Testes anterior to ovaries. 
• Fertilization external (in cocoon); development direct, no larval stages. 

1. Order - Plesiopora plesiothecata 

• Mostly aquatic. 
• Male gonopores on segment immediately following that which contains testes. 
• Spermathecae in the testes-containing segments, or nearby. 

 Examples: Aelosoma, Nais, Dero, Chaetogaster, Tubifex.

2. Order - Plesiopora prosothecata 

• Spermathecae far anteriorly to the segment containing testes. Examples: Enchvtraeus. 

3. Order - Prosopora 

• Mostly aquatic. 
• Male gonopores on the same segment containing testes, or on segment containing the second pair of testes. Example: Branchiobdella (parasitic). 

4. Order - Opisthopora 

• Mostly terrestrial earthworms. 
• Male gonopores some distance behind the testes-containing segments. 
• Examples: Lumbricus, Eisenia, Pheretima, Megascolex, Allolobophora,  Dendrobaena

3. Class – Hirudinea (L., hirudo- leech) 

• Freshwater, marine or terrestrial. 
• Generally, ectoparasite, blood-sucking and carnivorous. 
• Body with fixed number of segments (33). 
• Each segment subdivided externally into annuli. 
• Segmentation external without internal septa. 
• Parapodia and setae absent. 
• Both anterior and posterior ends of body with suckers. 
• Coelom much reduced due to its filling by botryoidal tissue, and forms haemocoelomic sinuses. 
• Hermaphroditic with one male and one female gonopore. 
• Fertilization internal. 
• Development in cocoons, direct without larval stages. 

1. Order - Acanthobdellida 

• Primitive without anterior suckers, proboscis and jaws. 
• Setae present in 5 anterior segments. 
• Coelom with compartments. 
• Example: A single Russian genus and species (Acanthobdella) parasitic on salmon. 

2. Order - Rhynchobdellida 

• Only aquatic leeches, ectoparasitic. 
• A protrusible proboscis with no jaws. 
• Coelom without compartments. 
• Bloodvasculare system separated from coelomic sinuses.
• Blood colourless.

3. Order - Gnathobdellida 

• Aquatic or terrestrial. 
• Ectoparasitic blood-sucking leeches. 
• Pharynx non-eversible with 3 pairs of jaws. 
• Examples: Hirudo, Hirudinaria, Haemadipsa. 

4. Order - Pharyngobdellida 

• Terrestrial and aquatic. 
• Some predaceous. 
• Pharynx non-protrusible. 
• No teeth but one or two style may be present. 
• Examples: Erpobdella, Dina. 

4. Class - Archiannellida (Gr., arch- First) 

• About one dozen genera of small, marine worms of unknown affinities. 
• Segmentation chiefly internal. 
• No parapodia and setae. 
• Sexes usually separate. 
• Usually, trochophore larva. 
• Example: Polygordius, Dinophilus, protodrilus. 

Hirudinaria granulose

Systematic Position: -

PHYLUM => ANNELIDA 

 CLASS    => HIRUDINEA 

 ORDER   => GNATHOBDELLIDA 

 FAMILY  => HEIRUDINAE 

 GENUS   => HIRUDINARIA

 Species    => granulos

Ecology: - 

• Hirudinaria granulose, the Indian cattle leech, is found in India, Burma, Sri Lanka, Pakistan and Bangladesh. 
• It occurs in fresh-water ponds, lakes, tanks, swamps and slow streams, where it either swim by vertical undulations or grips objects with its suckers and moves by looping. 
• Like most ectoparasitic leeches, it has a blood-sucking (sanguivorous) habit, feeding on the blood of fish and frogs and also of cattle and men, who happen to enter the water inhabited by it. 
• Though hermaphroditic, leeches copulate to bring about cross-fertilization. 
• Eggs are deposited in cocoons. 
• Body is elongated, Dorso-ventral-flattened and vermiform with flat ventral and convex dorsal surfaces. 
• Development is direct, i.e., there are no free larval stages in the life-history. 

Metamerism in Hirundinaria: - 

In annelids the body consists of segments arranged in a linear repetitive fashion. This linear repetition of body segment is called metamerism. Each section or part of the body is called segment, somite or metamer.

Metamerism segmentation is first seen in animal kingdom in the body of annelids. In metameric 

segmentation, body is divided into numerous body segments externally by groove and internally by septa. All the segments or metameres are same age and have all body organs such as musculature, blood vessels, nerves, ganglia, excretory organs and gonads etc. In earthworm and Nereis even the coelom is divided into segmental compartments by inter segmental septa.

But in annelids, the metamerism is limited to the trunk region of the body. The head with brain and 

sense organs is represented by prostomium and the terminal portion at the posterior end with 

anus is represented by pygidium.This two portions i.e., prostomium and pygidium are not true 

metameres. In annelids metameism is described as bring complete because all segments or 

metameres have segmented blood vessels, nerve, nephridia and coelom. Such segment also 

called homonomous. 

Significance of Metamerism: - 

1. Metamerism helps in locomotion in various ways. Annelids are able to locomotion like swimming and creeping by the help of the contraction of body wall muscles of body segments and coelomic fluid.
2. Coelomic fluid in coelomic chamber acts as an hydraulic skeleton during burrowing and swimming. 
3. In higher classes like Arthropods and Chordates, each metamere of body is specialized for different functions. Hence, higher and complex animals evolved due to metamerism.

Parasitic Adaptations in Hirundinaria:- 

Most leeches lead a semi-parasitic life, sucking blood of vertebrates. Correspondingly, they show several parasitic adaptations in their habits, habitat and structure. 

✔Habitat: -

It inhabits freshwater ponds and pools visited frequently by men and cattle. Moreover, it prefers to live in shallow waters where it can easily hide under weeds, logs and stones. 

✔Habits: -

Its active swimming habit is ideal for searching the host and escaping from predators. 

✔Shape: -

Body is long, flattened and devoid of appendages, like parapodia, and hence suitable for aquatic life. 

✔Slime gland: - 

These are present in body wall. Their secretion keeps the body moist and slippery to prevent desiccation and reduces friction during locomotion.

✔Suckers: -

These serve as organs of locomotion and also provide firm adhesion to the host’s body at the time of feeding. 

✔Jaws: -

The three jaws are specialized weapons for inflicting a painless triradiate wound on the host’s skin for sucking blood. 

✔Suctorial pharynx: -

Mouth leads into a muscular pharynx connected with body wall by radiating muscles. Cavity of pharynx alternately expands and contracts to serve as a suction pump so that blood, oozing from the host’s would, is sucked in. 

✔Hirudin: - 

Slivery glands of leeches secrete an anticoagulating substance, called hirudin or anticoagulin, It prevents clotting of blood while the leech is taking its meal, thus ensuring a continuous supply of blood (vampire bats and hook worms also secretes a similar 

substance to facilitate their feeding). 

✔Spacious crop: -

Chances of getting a host are remote, so that supply of nutrient is very irregular and a matter of chance. Digestive tract is accordingly modified. At the time of single meal a leech obtains many times its own weight of blood, which is sufficient for several months or even a year. To accommodate this blood, the crop is spacious thin-walled elastic and capable of great dilatation. It is also produced into lateral pouches or storing pockets. It can, therefore, hold enough blood to last for months. However, some species that parasitize aquatic vertebrates remain attached to their hosts. 

✔Slow digestion: -

After a meal, leech drops off, remains torpid and digests blood at a very slow pace. Last chamber of crop opens behind into stomach through a sphinctered aperture, so that blood passes from crop into stomach with extreme slowness. Digestion of a “crop full of blood” takes many months and thus a single meal lasts for several months. For this reason also leeches lack elaborate digestive juices and enzymes. 

✔Sense organs: -

These are well-developed and provide the animal with greater opportunities of life. 

✔Hermaphroditism: -

This doubles the rate of reproduction as, after copulation, both individuals lay eggs. 

✔Development: -

It takes place within the cocoon which serves as a protective covering. Further, development is quick, and completed within a fortnight to ensure the maintenance of a regular population.

Multiple choice questions:-

1. In leech locomotion occurs by: -

(a) Setae [ ] (b) Parapodia [ ] (c) Undulating movements [√] (d) All of these [ ] 

2. The saliva of leech contains an anticoagulant called: -

 (a) Histidine [ ] (b) Hirudin [√] (c) Heparin [ ] (d) Histamine [ ] 

3. Coelom filled with connective tissue and botryoidal tissue has come across in 

 (a) Earthworm [ ] (b) Nereis [ ] (c) Leech [√ ] (d) Ascaris [ ] 

4. Which one of the following is an ectoparasite annelid 

 (a) Hirudinaria [√] (b) Lumbricus [ ] (c) Pheretima [ ] (d) Ascaris [ ] 

5. Botryoidal tissue is found in 

 (a) Unio [ ] (b) Ascaris [ (c) Hirudinaria [√] (d) Nereis [ ]

 6. How many numbers of somites are present in the body of leech? 

 (a) 20 [ ] (b) 40[ ] (c) 50 [ ] (d) 33 [√] 

7. In leech the excretion is: -

(a) Uricotelic [ ] (b) Ammonotelic [√] (c) Ureotelic [ ] (d) None of these [ ]

8. Leech is 

(a) Carnivorous [ ] (b) Omnivorous [ ] (c) Sanguivorous [√] (d) Herbivorous [ ] 

9. Saliva of leeches contain an anticoagulant called 

 (a) Haemoglobin [ ] (b) Hirudin [√] (c) Heparin [ ] (d) Histamine. [ ] 

10. Common cattle leech belongs to the genus 

(a) Megascolex [ ] (b) Neanthes [ ] (c) Arenicola [ ] (d) Hirudinaria [√] 

11. The saliva of leech has an anticoagulant called

 (a) Heparin [ ] (b) Hirudin [√] (c) Chloragosomes [ ] (d) None of these [ ] 

  

12. How many chambers are found in the crop of leech? 

(a) Six [ ] (b) Eight [ ] (c) Nine [ ] (d) Ten [√] 

13. Leech is a blood sucking animal, nutritionally, therefore leech is 

(a) Herbivorous [ ] (b) Carnivorous [ ] (c) Sangivorous [√ ] (d) Omnivorous [ ] 

14. In which segment do you find the ovisac in leech? 

 (a) 8th [ ] (b) 11th[√] (c) 15th[ ] (d) 13th[ ]. 

15. Which segment possesses nephridia in Hirudinaria? 

 (a) 7-10th segment [ ] (b) 6-22 segments [√] (c) 10-20 segments [ ] (d) 7-18 segments [ ]

16. Female genital opening of Hirudinaria is present in 

(a) Ist annule of 10th segment [ ] (b) Ist annule of 11th segment [ ] (c) 2nd annule of 10th

(d) 2nd annule of 11th segment [√]

17. The posterior sucker of Hirudinaria is formed by the union of 

 (a) 1 segment [ ] (b) 7 segments [√] (c) 25 segments [ ] (d) 33 segments [ ]

18. The number of segments in Hirudinaria is 

 (a) 109 [ ] (b) 33[√] (c) 26 [ ] (d) Numerous [ ] 

20. In Hirudinaria space between body wall and canal is filled with the 

 (a) Botryoidal [√] (b) Connective tissue [ ] (c) Hoemocoelomic fluid [ ] (d) None [ ]. 

21. Hirudinaria is 

(a) Herbivorous [ ] (b) Carnivorous [ ] (c) Omnivorous [ ] (d) Sanguivorous [√] 

22. A temporary clitellum is formed in Hirudinaria’s segments 

 (a) 7th,8th and 9th[ ] (b) 9th to 11th[√] (c) 11th to 13th[ ] (d) None [ ] 

23. Number of annular receptor in each annulus 

(a) 18[ ] (b) 18 on dorsal and 18 on ventral [√] (c) 9 [ ] (d) None of the above. [ ] 

24. Hirudinaria contains 

(a) Slime gland [ ] (b) Sucker gland [ ] (c) Clitellar gland [ ] (d) All the above [√]

25. Velum is present in 

 (a) Pheretima [ ] (b) Hirudinaria [√] (c) Ascaris [ ] (d) All the above. [ ] 

26.In Hirudinaria there is no special organ for 

(a) Digestion [ ] (b) Excretion [ ] (c) Respiration [√] (d) Reproduction. [ ] 

27. Number of testes in Hirudinaria is: 

 (a) 10 pairs [ ] (b) 11 pairs [√] (c) 12 pairs [ ] (d) 13 pairs [ ]. 

28. How is phylum Anellida advanced over Nemathelminthes? 

(a)Metameric segmentation [ ] (b) True coelom [ ] (c) Closed circulation [ ] (d) All of the 

above [√] 

29. The animal bearing numerous setae are kept in class 

(a) Hirudinea [ ] (b) Oligochaeta [ ] (c) Polychaeta [√] (d) Onychophora [ ] 

30. In which class of phylum Annelida one pair of ovaries and many pairs of testes are found? 

(a) Polychaeta [ ] (b) Oligochaeta [ ] (c) Hirudinea (d) Archiannelida [ ] 

31. Which one of these is the primary characteristic of phylum Annelida? 

(a) Trochophore larva in life cycle [ ] (b) Metameric segmentation [√] (c) Excretion by flame 

cells [ ] (d) Body covered by ciliated epidermis. [ ] 

32. Aphrodite is commonly known as 

(a) Lung worm [ ] (b) Paddle worm [ ] (c) Sand worm [ ] (d) Sea mouse [√]

33. Larval form of Polychaeta is known as 

(a) Tornaria [ ] (b) Glochidium [ ] (c) Trochophore [√] (d) Bipinnaria [ ].

34. Smooth blood worm is 

(a) Aphrodite [ ] (b) Glycera [ ] (c) Hirudinaria [√] (d) Terebella [ ] 

35. In Lumbricus, clitellum is present in segments 

(a) 33 to 37 [√] (b) 22 to 27 [ ] (c) 54 to 60 [ ] (d) 46 to 56 [ ] 

36. A triploblastic, bilaterally symmetrical, elongated and vermiform body is characteristic of 

(a) Coelenterates [ ] (b) Arthropods [ ] (c) Annelids [√] (d) None of the above [ ] 

37. Tube dwelling polychaetes are known as 

(a) Burrowing [√] (b) Planktonic [ ] (c) Pelagic [ ] (d) Tubicolous [ ] 

38. In Polychaeta, the nature of seta is 

(a) Numerous [√] (b) Occur singly [ ] (c) Occur in bundles [ ] (d) Fused [ ] 

39. Presence of coelom and metamerism are the most important characters in 

(a) Helminths [ ] (b) Arhhropods [ ] (c) Annelids [√] (d) Coelenterates [ ] 

40. The origin of the nephridium is 

(a) Germinal [ ] (b) Ectodermal [ ] (c) Mesodermal [√] (d) Endodermal [ ] 

41. Cuticle of annelids is 

(a)Non-chitinous and albuminoid (b) Chitinous [√] (c) Chitinous albuminoid [ ] (d) Non 

chitinous [ ] 

42. The body cavity of Hirudo is filled with 

(a) Connective tissue [ ] (b) Parenchyma tissue [ ] (c) Botryoidal tissue [ ] (d) Coelomic fluid [√] 

43. Tube within a tube body plan is found in 

(a) Pheretima posthuma [ ] (b) Hydra [ ] (c) Rana tigrina [√] (d) Lepus cuniculus [ ] 

44. Arenicola is commonly known as 

(a) Lugworm[√] (b) Paddle worm[ ] (c) Sea pen [ ] (d) Potato worm. [ ] 

45. Nereis is commonly known as 

(a) Clam worm [√] (b) Earthworm [ ] (c) Skate sucker [ ] (d) Sea fan. [ ] 

46. Sucking of human blood by the leech is called 

(a) Blood sucking [√] (b) Phlebotomy [ ] (c) Autotomy [ ] (d) Phrynotomy [ ] 

47. The coelom in Annelida is 

(a) Pseudocoelic [ ] (b) Enterocoelic [ ] (c) Schizocoelic [√] (d) Acoelous [ ]

48. Lug worm is scientifically known as 

(a) Nereis [ ] (b) Arenicola [√] (c) Aphrodite [ ] (d) Polynoe [ ]

49. Sabella is generally known as 

(a) Rag worm [ ] (b) Scale worm [ ] (c) Peacock worm [√] (d) None [ ] 

50. Which is known as blood worm? 

(a) Terebella [ ] (b) Tubifex [ ] (c) Lumbricus [√] (d) Nereis [ ]. 

51. The ‘Tubifex’ is 

(a) Blood parasite [ ] (b) Sand dweller [√] (c) Fresh water [ ] (d) Parasite [ ]. 

52. Medicinal leech is 

(a) Hirudinaria [ ] (b) Hirudinaria japanica [ ] (c) Hirudo medicinalis [√] 

 (d) Hirudinaria viridis [ ] 

53. Sipunculus is commonly known as 

(a) Nut worm [ ] (b) Pea nut worm [√] (c) Peacock worm [ ] (d) None [ ] 

54. The annelid larva is 

(a) Bipinnaria [ ] (b) Trochophore [ ] (c) Cercaria [√] (d) None [ ]

Terminal Question :-

1. Write important adaptive features of Hirudinaria? 

2. Describe the features indicating the adaptations of leech to lead an ectoparasitic life? 

3. Which organs does the female reproductive system of leech comprise? Write the location of 

ovaries? 

4. Write, in brief, about the mode of locomotion of leech? 

5. Write a short note on haemocoelomic system of leech? 

6. In how many classes is phylum Annelida divided? 

7. Give the name of larvae of Annelida? 

8. Name the kind of segmentation found in annelids?

9. What is the feeding habit of Hirudinaria? 

10. How many testes are present in Hirudinaria? 

Phylum Aschelminths, general character of Phylum Aschelminths, function, example, Objective question of Aschelminths,

 Phylum Aschelminths

There are several groups of animals in which the space inside the body is a pseudocoel. It is not a true coelom because it is not lined with mesodermal epithelium and represents a persistent embryonic blastocoel. These groups of animals are known as pseudocoelomates (presence of a cavity, the pseudocoel, between the gut and body wall), and they are often placed within a single super phylum aschelminths. Gegenbaur (1859) created a group nemathelminth to place some pseudocoelomates animal. The name aschelminths was proposed by grobben (1910), in place of the older name 

nemathelminths. It has been derived from two Greek words: askes - cavity + helmins – worm.

GENERAL CHARACTERS: -

• Mostly aquatic, free living or parasitic.
• Usually small, even microscopic. Some reach a meter or more in length.
• Body slender, vermiform, unsegmented, flatter cylindrical, bilaterally symmetrical and triploblastic.
• Organ system grade of body organization.
• Head not distinctly formed with well-defined sense organs.
• Body wall with a syncytial or cellular epidermis externally covered with thick cuticle of scleroprotein. 
• Cilia absent except anterior cilia of rotifers.
• Musculature includes mostly longitudinal fibers.
• Body cavity pseudocoel not lined by mesoderm.
• Digestive canals complete with mouth, specialized pharynx, straight non-muscular intestine and posterior or anus.
• No circulatory and respiratory systems.
• Excretory system is of protonephridia and canals. 
• Cloaca is present in some species.
• Nervous system of cerebral ganglia, or of circumenteric nerve ring with anterior and posterior nerves.
• Mostly dioecious. Male usually smaller than female.
• Gonads and ducts single or double. 
• Eggs with chitinous shell. Cleavage is determinate and spiral.
• Development usually direct with no larval stages, or indirect with a complicated life history.

Important notes: -

The name aschelminths was proposed by grobben (1910), in place of the older name nemathelminths. It has been derived from two Greek words: askes - cavity + helmins – worm. Mostly aquatic, free living or parasitic. Usually small, even microscopic. Some reach a meter or more in length. Body slender, vermiform, unsegmented, flat or cylindrical, bilaterally symmetrical and triploblastic. Body cavity pseudocoel not lined by mesoderm. Digestive canals complete with mouth, specialized pharynx, straight non-muscular intestine and posterior anus. No circulatory and respiratory systems. Excretory system of protonephridia and canals. Nervous system of cerebral ganglia, or of circumenteric nerve ring with anterior and posterior nerves. Mostly dioecious. Male usually smaller than female. Gonads and ducts single or double. Eggs with chitinous shell. Cleavage determines and spiral. Development usually direct with no larval stages, or indirect with a complicated life history

Aschelminths includes one very large group (nematode) and four smaller groups (rotifer, gastrotricha, kinorhyncha and nematomorpha). According to some zoologists such as Hyman (1951), aschelminths is regarded as a distinct phylum, and the various groups included in it as classes. However, others treat different groups as separate phyla and the name of aschelminths as a superphylum or without any taxonomic rank. Modified classification was proposed by storer and Usinger (1971).

Ascaris lumbricoides, commonly known as round worm. It is largest nematode parasite in the human intestine. It is found more commonly in children than in adults. It is a large size nematode showing sexual dimorphism. The female length measures 20-40 cm in length and 6-8 mm to width. Fresh specimens are pale pink or flesh colored body. The body wall is formed of following three layers: a). Cuticle b). Epidermis c). Muscle layer. There are no respiratory organs in Ascaris. The parasites carry on anaerobic respiration as the oxygen content in the intestine of host is very poor. The excretory system is in the shape of H. Ascaris excretes more urea when water is scarce. A female Ascaris is recorded to lay as many as 27,000,000 eggs. Eggs of Ascaris are about 40-75 (microns) in size and elongated elliptical or oval in form. The eggs become stained yellowish or brown in the intestine. No secondary host in the life history of Ascaris. The Ascaris larvae inside the lungs cause inflammation and produce severe and fatal pneumonia. Sometimes their presence causes fever, anaemia, leukocytosis and eosinophiles. Piperazine salt is the ideal drug administered for Ascaris.

👉Objective question of Platyhelminthes: -

1)Pseudocoelom is present in: -

(a)Aschelminths (b) Platyhelminthes (c)Coelenterates (d) Annelida 

2)Organ system of body organization presents in: -

(a) Porifera (b) Platyhelminthes (c)Aschelminths (d) Coelenterate 

3)In Rotifer the sense organs are: -

(a) eye spot (b) antennae (c) statocyst and eye spot (d) eye spot and antennae 

4)Development of Gastrotricha  is: -

(a) Direct (b) indirect (c) parthenogenetic (d) regenerative 

5)One of these known as hair worms: -

(a) Rotifer (b) Kinorhyncha (c) Nematomorpha (d) Nematoda

6)Juvenile parasite in grasshopper and other insects: -

(a) Rotifera (b) Kinorhyncha (c) Nematomorpha (d) Nematoda

7)Digestive system present complete with muscular pharynx and glands: -

(a)Nematoda (b) Nematomorpha (c) kinorhyncha (d) Gastrotricha 

8)digestive system with a grinding mastax in animal of phylum: -

(a) Rotifers (b) Gastrotricha (c)Kinorhyncha (d) Nematomorpha 

9) Which type of body is found in Ascaris?

(a) Gastrovascular (b) Pseudocoelom (c) Coelom (d) none of these

10)In life cycle of Ascaris, the juvenile hatches out of egg in: -

(a) Lung (b) Liver (c) Intestine (d) None of these

11)The mouth of Ascaris lumbricoides is bound by three lips of which: -

(a)One is median and two are lateral (b) One is dorsal and two are ventral (c) Two are dorsal and one is ventral (d) One is median and dorsal and two are ventrolateral. 

12)Normal life span of Ascaris is: -

(a) 9-12 weeks (b) 9-12 months (c)9-12 years (d) 3-4 months 

13)Ascaris has well developed: -

(a) Nervous system (b) Reproductive system (c)Receptors (d) Digestive system 

14)Ascaris is not: -

(a)Endoparasite (b)Monogenetic (c) free living (d) Dioecious 

15)Respiration in Ascaris is: -

(a)Aerobic Reproduction (b) Anaerobic Reproduction (c)Both (d)none of these 

16)Ascaris, being a parasite possesses reduced sense organs called: -

(a)Amphids (b) Penial setae (c) Penial papillae (d)post-anal papillae 

17)Infection of Ascaris usually occurs by: -

(a)Contaminated water and vegetable (b)Tse-Tse fly (c)Both (d)none of these

18) The space between alimentary canal and body wall in Ascaris is: -

(a) Parasole (b) haemocoel (c) Pseudocoel (d)Gastrocoel 

19)Special feature of sperms of Ascaris is: -

(a)With tail (b) more than one tail (c) Without tail (d) Largest 

20)In Ascaris, how many juveniles are formed from fertilized egg up to adult: -

(a)1 (b)2 (c)3 (d) 4

21)Female Ascaris can be differentiated from male Ascaris by: -

(a)Straight posterior end (b) Curved posterior end (c)Smaller size (d)Genital papillae. 

22)During development, Ascaris needs: -

(a)One intermediate host (b) Two definite hosts (c) No intermediate host (d) No definite host 

23)From the egg of Ascaris, first larva hatches in 

(a) Uterus of female Ascaris (b) outside the body of host (c) Stomach of Host (d)Intestine of host 

24)The first juvenile larva of Ascaris is known as: -

(a)Miracidium larva (b) Microfilariae (c) rhabditiform larva (d) filiform larva 

25)Which type of excretory canal system is present in Ascaris: -

(a) C-shaped (b)J- shaped (c) H-shaped (d) W-shaped 

26)In Ascaris, the reserve food is stored as glycogen and fats in: -

(a) Intestine (b) muscles (c)Hypodermis or epidermis (d) all of these 

27)In which of the animals, the syncytial epidermis follows the cuticle?

(a)Fasciola (b) Ascaris (c)taenia (d) Earthworm 

28)Excretory organ in Ascaris is: -

(a)nephridia (b)Kidneys (c) Flame cells (d) None of these   

29)Two sexes of Ascaris can be identified as: -

(a)Posterior end of female is straight (b)Anal papillae are found in male (c)female has vulva (d) all of these. 

30)Penial setae arise from; - 

(a) Cloaca of male (b) Anus of female (c)Vulva of female (d) none of these

31)In Ascaris, egg is fertilized in: -

(a)Oviduct (b)Uterus (c) Vagina (d) Outside human body 

32) Egg of Ascaris passed out of host's body are: -

(a)Unfertilized (b) fertilized (c) Fertilized and shelled (d) With a larva. 

Answer Key: -

(1) a (2) c (3) d (4) a (5) c (6) d (7) a (8) a (9) b (10) c (11) d (12) b (13) b (14) c (15) b (16)a (17) a (18) c (19) c (20) d (21) a (22) c (23) d (24) c (25) c (26) c (27) b (28) d (29) d (30) c (31) c (32) d