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