Phylum Coelenterate, general characteristic of coelenterate, Function of coelenterate, Objective question of Coelenterate, Terminal question of Coelenterate,

 Phylum Coelenterates 

Phylum Cnidaria (formally known as coelenterate) includes about 9000 species. Some are found in fresh water, but the greater numbers are marines. Coelenterates (Gr. koilos- hollow + enteron- gut) are the simplest of eumetazoans. This interesting group of animals takes its name from the large cavity in the body that serves as the intestine. They include the hydra, jellyfish, sea anemones and corals. 

General Characters: -

✔Coelenterate are metazoan or multicellular animals with tissue grade of organization. 

✔2Body radial or bi-radially symmetrical with oral-aboral axis. 

✔3They are diploblastic animals. 

✔Coelenterate animals are represented by two morphologically different types of individuals, polyps and medusa. 

✔Polyps are sessile (attached to the substratum) with a tubular body (e.g., Hydra). Whereas medusas are free-swimming with an umbrella or bell-shaped body, e.g., Aurelia, Metridium. 

✔They are all aquatic, mostly marine and some freshwater (e.g., Hydra). 

✔They may exhibit solitary or colonial habitat. 

✔One of the most characteristic structures of all coelenterates is the stinging cells, called nematocysts. 

✔Nematocysts serve for adhesion, food capture and offence and defence. 

✔They have a single gastro-vascular cavity, into which mouth opens. 

✔Short and slender tentacles encircle the mouth in one or more whorls. 

✔Coelenterate animals are usually carnivorous. 

✔The coelom, excretory, circulatory and respiratory organs are absent

✔ Anus is absent. 

✔ Locomotion is brought about by smooth muscle fiber.

✔Nervous system consists of one or more networks or nerve cells and neurites located in the ectoderm and endoderm. 

✔Sense organs are ocelli and statocysts. 

✔Skeleton either calcareous or horny and external or internal but absent in few. 

✔Reproduction is both asexual and sexual methods. 

✔Asexual reproduction occurs by budding and sexual reproduction by the formation of gametes. 

✔The Planula larva present in the life history of Coelenterata. 

✔The life history exhibits the phenomena of alternation of generations or metagenesis in which the asexual polypoid, sessile generation alternates with sexual medusoid, free-swimming generation.

Alternation of Generation: - 

Life history of Aurelia exhibits the phenomenon of “alternation of generation” since the sexual medusoid form always alternates with the asexual polypoid from. The fee-swimming adults Aurelia (medusoid form) represents sexual generation and reproduces by the formation of gametes. The fertilized ovum develops into a fixed polypoid scyphi stoma through a free-swimming planula larva. The polypoid scyphi stoma represents asexual generation and reproduces asexual by budding.

A brief account of coral and coral reefs and their importance: - 

Corals: - 

Meaning of coral: - 

Coral animals or corals are marine, mostly colonial, polypoid coelenterates, looking like miniature sea anemones and living in a secreted skeleton of their own. Their calcareous or horny skeleton is also commonly known as coral. Some corals grow into massive, solid structures; others form large, branched colonies. Most of the corals belong to the class Anthozoa and the few to class Hydrozoa of phylum coelenterate. 

Structure of coral polyp 

1.  Soft structure A typical coral polyp from a colony is a small organism about 10 mm long and 1 to 3 mm in diameter. A basal disc is absent because the basal region of polyp is surrounded by a calcareous exoskeleton. Oral disc bears numerous tentacles, in several rows around an elongated, oval or circular mouth. Pharynx or stomodaeum is short and without siphonoglyphs. Mesenteries are restricted to the upper part of coelenteron and mesenterial filaments contain only one glandular lobe bearing nematocysts. Body wall is without cinclids and nematocyst bearing structures (acontia). Muscles are poorly developed while little is known about nervous system. Living polyps are found only on surface layers of coral masses. They feed at night both by raptorial and suspension feeding. When not feeding, they withdraw into cup-like cavities of skeleton.
2. Structure of coral skeleton: - Skeleton of solitary coral is known as corallite. It is a calcareous exoskeleton secreted by epidermis. In a colonial coral, corallites of individual polyps fuse together to form a skeletal mass, called Corallium. Each corallite is like a stony cup with a basal part or basal plate, and a cup wall or theca, enclosing the aboral portion of polyp. Cavity of cup contains a number of vertical radiating ridges called sclerosepta, proceeding from theca towards the center of cup. Inner ends of sclerosepta are fused to form an irregular central skeletal mass or columella. 

Types of corals in different groups: - 

1. Hydrozoan corals: -Order hydrocorallina includes few genera, like millepora, stylaster and distichopora, which are colonial and secrete massive branched calcareous exoskeletons. These are found in coral reefs with other corals. Skeleton is secreted by a modified epidermis, called calicoblastic layer. Living within the skeleton occur two types of polyps, large feeding gastrozooids and defensive dactylozooids. 
2. Octocorallian corals: - (a)Order alcyonaceaincludes marine, colonial and soft corals. A well-known genus is alcyonium, popular as “dead man’s fingers” because of its resemblance to a human hand. It has an endoskeleton of separate calcareous spicules embedded in a massive mesoglea or coenenchyma. 

(b)Order stolonifera includes the organ pipe coral, tubipora musica, widely distributed on coral reefs in warm waters. Skeleton is made of mesogloeal calcareous spicules forming parallel and vertical tubes, each occupied by one polyp, and connected together by lateral platforms. Skeleton is dull red in colour due to presence of iron salts. 

(c)Order coenothecalia includes a single genus heliopora, commonly known as blue coral. Its massive calcareous, skeleton or Corallium is secreted by polyps living in large, erect, cylindrical solenialtubes on the surface of skeleton. 

3. Hexacorallian corals: -

Order madrepora includes stony corals, which are the principal builders of coral reefs. While 

some of them are solitary, most are colonial, assuming a great variety of forms.

(a) Solitary corals: - Fungia, flabellum, etc., are the solitary corals or cup corals. The corallite is disc-like or mushroom shaped in form and measures 5 mm to 25 cm across. 

(b) Colonial corals: -Most of stony corals are colonial with plate –like, cup-like, spherical, or vase-shaped skeleton. Typical examples of colonial medreporarian corals are acropora, oculina, favia, madrepora, etc. Some of the colonies are branched. 

Coral Reefs 

Coral colonies grow continuously in size by budding of polyps and often form extensive masses, known as coral reefs. According to T.Wayland Vaughan (1917), a coral reef is a ridge or mound of limestone, the upper surface of which is near the surface of sea, and which is formed chiefly of CaCO3 secreted by coral polyps. Principal builders of coral reefs are stony corals (madreporians), but other important contributors are the hydrocorallines and alcyonarians. Coralline algae and foraminiferan protozoa also take part in the formation of coral reefs.Reef building corals require warm shallow waters (normally above 20C). They are therefore limited to the Indo-pacific, the central western pacific, and the carabian regions north of Bermuda. About 50 species of corals contribute in the formation of reefs along the Florida Keys and in the West Indies. 

Kinds of coral reefs 

The coral reefs are of three kinds, depending on how they are formed: -

1.)Fringing reefs: - Coral reefs lying close to the shores of some volcanic islands or pert of some continents are termed fringing reefs. Fringing reefs may extend out to a distance of a quarter mile from the shore with the most active zone of the coral growth facing the sea. This seaward zone is commonly called the edge or front. A shallow water channel, 50 to 100 meters broad, lies between the reef-edge and shore at low tide, water of channel recedes at quickly exposing a flatbottom surface, called reef flat. It is largely composed of coral sand, mud dead and living coral colonies and other animals. 

2). Barrier reefs: - Barrier reefs are like fringing reefs, but they are located some distance away from the shore. The stretch of water, separating the barrier reef from land, may be half a mile to 10 miles or 

more in width. It is called a lagoon. It is 10 to 50 fathoms deep and suitable for navigation. Most notable example of barrier reefs is the Great Barrier Reef along the north- eastern coast of Australia. It is about 2000 km long and up to 150 km from shore.

3.) Atoll: -An atoll is also termed a coral island or lagoon island. It is a ring-like or horse-shoe shaped reef that encircles a lagoon but not an island. The lagoon varies from a few to about 90 km across. It may be complete or broken by a number of channels, of which only a few are navigable. Outer side of the reef slopes off rather steeply into the depth of ocean. The atoll of Bikine, famous for atomic and hydrogen bomb tests, lies in the Pacific Ocean.

Economic importance of coral reefs: - 

Corals of the remote geological past formed reef structures. They were highly favorable sites for 

accumulation of petroleum deposits. Thus, coral reefs are of much importance to oil industry. Large quantities of corals are shipped every year for the curio trade. The coral reefs serve as habitats for many plants and animals like sponges, molluscs, echinoderms, fishes, etc. Some coral reefs are used for habitations by man as well. Some corals are highly prized for their decorative value. Corallium rubrum is considered to be a precious coral stone in India and china and treated as auspicious. The red coral and organ pipe coral are used in some indigenous system of medicine in India Chunks of coral skeleton belonging to species Porites are used as building materials. Coral skeletons serve as raw material for the preparation of lime, mortar and cement because of their calcium carbonate and magnesium carbonate content. Coral reefs serve as good nursery grounds for commercially important fishes. Reef fish varieties are more colourful than others. 

💥Objective question of Phylum Coelenterata :--

1)Nematocysts are found in: - 

(a)Porifera (b) Coelenterata (c) Platyhelminthes (d) Annelida 

2)The mesenteries attached to the stomodeum are known as: -

(a)Primary (b) secondary (c) tertiary (d) directives 

3)The function of a dactylozooid in polymorphic colony is: -

(a)nutrition (b) reproduction (c) locomotion (d) offence & defence 

4)Polymorphism is found in: -

(a)Halistemma (b) Leucernaria (c) Zoanthus (d)Alcyonium 

5)Pneumatophore is absent in: -

(a)Diphyes (b)Halistemma (c) Physalia (d) Porpita 

6)Gonozooid with a mouth is found in: -

(a)Physalia (b) Velella (c) Porpita (d) all of these 

7)Hypnotoxin is a poisonous fluid produced by: -

(a)parasitic protozoa (b)nematocysts (c) Ascaris (d)sponges 

8)Gastric filaments occur in: - 

(a)Hormiphora (b) Aurelia (c)Obelia (d) Ctenophores 

9)Which of the following inhabit freshwater bodies?

(a)Scyphozoans (b)anthozoans (c)Hydrozoans (d)Ctenophores 

10)The animal without sexual medusa: -

(a)Hydra (b)Millepora (c)Velella (d) Halistemma

11)The function of a tentaculocyst in Aurelia: -

(a)photoreception (b)chemoreception (c)balancing (d)reproduction 

12)Float is not found in: -

(a)Physalia (b) Velella (c)Porpita (d) Obelia 

13)An example of a soft coral: -

(a)Tubipora (b)Heliopora (c)Alcyonium (d)Gorgonia 

14)Which of the following is connected with Coral formation: -

(a)  Halistemma (b)Millepora (c)Adamsia (d)Rhizostoma

15)The scientific name of precious red coral: -

(a)Tubipora (b)Fungia (c)Heliopora (d) Corallia

16)A sea anemone was found growing on a Costopodia shell occupied by a hermit crab: -

(a)symbiosis (b)commensalism (c)competition (d)neutralism

17)Which of the following is the probable reason or such association?

(a)Sea anemone cannot live without the hermit crab (b) Hermit crab benefits by being protected by the Sea anemone (c) Both of them (d) All of them 

18)Fringing reef is usually located: -

(a)very near the shore (b) away from the shore (c)in the deep sea (d)in the Island 

19)The larva of Physalia is: -

(a)a Planula (b)an ephyra (c)a cydippid larva (d)a scyphistoma

20)Example for a permanently sessile Scyphozooa is: -

(a)Aurelia (b)Lucemaria (c) Pelagia (d)Pilema

21)'Hedgehog hydroid commonly known as: -

(a)Tubularia (b)Hydructinin (c)Pennaria (d)Physalia  

22)'Fire coral ' is known as: -

(a)Tubularia (b)Pennaria (c)Millepora (d) Physalia    

23)The nature of Hydra is: -

(a)herbivorous (b)carnivorous (c) omnivorous (d)none of these 

24)Mesogloea secreted by: -

(a)ectoderm (b) Endoderm (c)Both of theme (d)All of them 

25)Most sensitive region of the body of Hydra: -

(a)Mouth (b)tentacle (c)basal disc (d)bud 

26)Peanatula region of the body of Hydra: -

(a)sea fun (b)sea fish (c)sea disc (d)sea pen 

27)Which is known as mushroom coral: -

(a)Fungia (b)Tubipora (c)Adamsia (d)Aurelia

28)Dead man's finger is: -

(a)Fungia (b)Alcyonium (c)Corallium (d)Heliopora

29)Prototheen is a: -

(a)Nutritive secretion (b)Skeleton rudiments (c)All of these (d)None of these 

30)Most important example of barrier reef is: -

(a)Florida keys (b)West Indies (c)Great Barrier Reef (d)None of these 

💥Answer key: -

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

Terminal Questions: -

1.Write short notes on: -

(a)Coral reefs.

(b)Fringing reef.

(c)Barrier reef.

2.What is corallite? Discuss coral reefs, in brief?

3.Write notes on:

(a)Generalised polyp and medusa.

(b)Corallite.

(c)Types of coral reefs.

4.How are coral reefs formed?

5.Differentiate between atoll, barrier reef and fringing reef?

6.Write the outline classification of Phylum Coelenterates?