BIOLOGY HOLIDAY HOMEWORK

1. BIOLOGY HOLIDAY HOMEWORK NAME- VAISHALI GUPTA CLASS - 11-A ROLL NO.- 26

2. TOPIC:- ASCHELMINTHES (ROUNDWORMS)

3. ROUNDWORM

4. KEY DEFINITION • The Aschelminthes (also known as Aeschelminthes), closely associated with the Platyhelminthes, are an obsolete phylum of pseudocoelomate and other similar animals that are no longer considered closely related and have been promoted to phyla in their own right. The term Aschelminth is now generally only used as an informal name for any member of the approximately ten different invertebrate phyla formerly included within Aschelminthes.

5. GENERAL CHARACTER

6. BODY FORM • The body is cylindrical. • The body is tapering at both ends. • The body is without segmentation. • The body is bilateral in roundworm. • The roundworms are triploblastic. • They have organ-system level of organization. • Te anterior end does not form a distinct head. • There are no locomotory appendages in roundworm.

7. Body wall • The body wall consists of firm , nonliving, resistant cuticle, epidermis and muscle layer. The cuticle is moulted (changed) four times during growth period . • The epidermis is syncytial (a continuous layer of cytoplasm having scattered nuclei) , but lacks cilia. It is thickened into 491 dorsal, 1 ventral, and 2 lateral)chords that project into the body cavity. • The musculature contains longitudinal fibers only.

8. Body cavity • A cavity is present between the body wall and digestive system tract. It is not lined by mesothelium. Therefore, it is called the pseudocoelom instead of coelom. • It contains pseudocoelomic fluid .

9. Body covering (from ectoderm) Muscle layer (from mesoderm) Pseudocoelom Digestive tract (from ectoderm) • A pseudocoelom • Is a body cavity derived from the blastocoels, rather than from mesoderm Pseudocoelomates such as nematodes have a body cavity only partially lined by tissue derived from mesoderm.

10. skeleton • There is no mineralized skeleton . • High fluid pressure in the pseudocoelom maintains body shape. • It is called hydroskeleton.

11. Digestive system • INGESTION: Food enters the mouth through the pharynx. • DIGESTION: Food is passed into the intestine where nutrients are broken down and absorbed. • ELIMINATION: Undigested food wastes leave through anus.

12. Digestive tract • There is a straight, one-way digestive tract with mouth as well as anus. Such a digestive tract is said to be complete. • It allows food to move on without mixing successive meals and faeces to pass out of the anus. • Mouth is bordered with 3-6 lips having sensory papillae. • Pharynx is muscular with 3-rayed cavity. It is used to suck the food . Intestine is nonmuscular.

13. respiration • Respirations in roundworm occurs through simple diffusion.

14. Circulatory system • The circulatory system is undeveloped.

15. Nervous system • The nervous system is intraepidermal. • It comprises a circumpharyngeal ring that sends nerves forward as well as backward. • Sense organs (papillae, amphids) are present on the lips. Amphids are chemoreceptors.

16. Excretory system • The excretory system consists of gland cells or intracellular canals or of both. • Excretory matter is mainly ammonia (ammoniotelism).

17. Excretory tract • Nitrogenous waste enters the two excretory tubules. • Excretory tubules empty into an excretory pore at the anterior (head) end of the worm

18. reproduction • Sexes are generally separate. Sexual dimorphism is present. • Males are smaller than females , their hind end is curved ventrally, and they have penial spicules to aid in copulation. • Males genital tract joins the digestive tract to form a cloaca.

19. Female genital tract opens out independently. • Eggs are unbelievably numerous and resistant to environment extremes. • Fertilization is internal. • There is no asexual reproduction. • Development of eggs are direct.

20. Natural history • The roundworms range from less than 1 m. to more than 1m in length, occurs everywhere – in fresh water, sea-water and soil. • A hectare of humus rich soil may harbour several hundred billion microscopic free-living nematodes.

21. Natural history • Many lives as parasite in plants and animals. Humans about 50 nematodes species . • The nematodes cause serious agricultural, veterinary, and human health problems. • The roundworms show peculiar twisting movements. • There are over 90,000species of nematodes. Their number will rise in the years to come.

22. Unique features • Syncytial epidermis • Body wall musculature of longitudinal fibres only. • Pseudocoel, a body cavity without a lining of mesodermal coelomic epithelium. • Nonmuscular intestine

23. Advancement over flatworms The round worms show advancement over the flatworm in having:- • Complete digestive tract, • Fluid filled body cavity, • Separate sexes.

24. SUB-DIVISIONS • Acanthocephala -- spiny-headed parasitic worms; about 1150 species known • Chaetognatha -- arrowworms; about 70 species known. • Cycliophora -- cycliophorans; 1 species known, microscopic • Gastrotricha -- gastrotriches; about 430 species known, all microscopic • Kinorhyncha -- kinorhynchs; about 150 species known, all microscopic • Loricifera -- loriciferans; about 10 species described, all microscopic • Nematoda -- nematodes or roundworms; about 12,000 species known, but an estimated 200,000+ species extant, mostly microscopic • Nematomorpha -- horsehair worms; about 320 species known • Priapulida -- priapulid worms; 16 species known, abut half microscopic • Rotifera -- rotifers or "wheel animalcules"; about 1500 species known, all microscopic

25. acanthocephala • Acanthocephala  is a phylum of parasitic worms known as acanthocephales, thorny-headed worms, or spiny-headed worms, characterized by the presence of an evertable proboscis, armed with spines, which it uses to pierce and hold the gut wall of its host. Acanthocephalans typically have complex life cycles, involving a number of hosts, including invertebrates, fishes, amphibians, birds, and mammals. About 1150 species have been described.

26. acanthhocephala • The Acanthocephala were thought to be a discrete phylum. Recent genome analysis has shown that they are descended from, and should be considered as, highly modified rotifers. This is an example of molecular phylogenetics.

27. CORYNOSOMA WEGENERU

28. chaetognatha • Chaetognatha, meaning hair-jaws, and commonly known as arrow worms, are a phylum of predatory marine worms that are a major component of plankton worldwide. About 20% of the known species are benthic, and can attach to algae and rocks. They are found in all marine waters, from surface tropical waters and shallow tide pools to the deep sea and polar regions. Most chaetognaths are transparent and are torpedo shaped, but some deep-sea species are orange. They range in size from 2 to 120 millimeters (0.079 to 4.7 in).

29. chaetognatha • There are more than 120 modern species assigned to over 20 genera. Despite the limited diversity of species, the number of individuals is large.

30. Spadella cephaloptera

31. cycliophora • Symbion is the name of a genus of aquatic animals, less than ½ mm wide, found living attached to the bodies of cold-water lobsters. They have sac-like bodies, and three distinctly different forms in different parts of their two-stage life-cycle. They appear so different from other animals that they were assigned their own, new phylum Cycliophora shortly after they were discovered in 1995. This was the first new phylum of multicelled organism to be discovered since the Loricifera in 1983.

32. cycliophora • The genus Symbion are peculiar microscopic animals, with no obvious close relatives, and which was therefore given its own phylum, called Cycliophora. The phylogenetic position of Symbion remains unclear: originally the phyla Ectoprocta and Entoprocta were considered possible relatives of Symbion, based on structural similarities. However, genetic studies suggest that Symbion may be more closely related to Gnathifera.

33. CYCLIOPHORA

34. gastrotricha • The gastrotriches , often called hairy backs, are a phylum of microscopic (0.06-3.0 mm) animals abundant in fresh water and marine environments. Most fresh water species are part of the periphyton and benthos. Marine species are found mostly interstitially in between sediment particles, while terrestrial species live in the water films around grains of soil.

35. GASTROTRICH

36. kinorhyncha • Kinorhyncha  is a phylum of small (1 mm or less) marinepseudocoelomateinvertebrates that are widespread in mud or sand at all depths as part of the meiobenthos. They are also called mud dragons.

37. KYNORHYNCHA

38. loricifera • Loricifera  is a phylum of very small to microscopic marine sediment-dwelling animals with twenty-two described species, in eight genera. Aside from these described species, there are approximately 100 more that have been collected and not yet described. Their size ranges from 100 µm to ca. 1 mm.They are characterised by a protective outer case called a lorica and their habitat, which is in the spaces between marine gravel to which they attach themselves. The phylum was discovered in

39. loricifera 1983 by Reinhardt Kristensen, in Roscoff,France. They are among the most recently discovered groups of Metazoans. They attach themselves quite firmly to the substratum, and hence remained undiscovered for so long. The first specimen was collected in the 1970s, and later described in 1983. They are found at all depths, in different sediment types, and in all latitudes.

40. Pliciloricus enigmatus

41. nematoda The nematodes or roundworms (phylum Nematoda) are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. The total number of nematode species has been estimated to be about 1,000,000. Unlike cnidarians or flatworms, roundworms have tubular digestive systems with openings at both ends.

42. NEMATODE

43. nematomorpha • Nematomorpha (sometimes called Gordiacea, and commonly known as horsehair worms or Gordian worms) is a phylum of parasiticanimals that are superficially morphologically similar to nematode worms, hence the name. They range in size in most species from 50 to 100 centimeters (20 to 39 in) long and can reach in extreme cases up to 2 meters, and 1 to 3 millimeters (0.039 to 0.12 in) in diameter. Horsehair worms can be discovered in damp areas such as watering troughs, streams, puddles, and cisterns. The adult worms are free living, but

44. nematomorpha the larvae are parasitic on beetles, cockroaches, orthopterans, and crustaceans. About 351 species are known and a conservative estimate suggests that there may be about 2000 species worldwide. The name "Gordian" stems from the legendary Gordian knot. This relates to the fact that nematomorpha often tie themselves in knots.

45. Paragordius tricuspidatus

46. priapulida • Priapulida is a phylum of marine worms. They are named for their extensible spiny proboscis, which, in some species, may have a shape like that of a human penis. They live in the mud, which they eat, in comparatively shallow waters up to 90 meters (300 ft). • Together with Echiura and Sipuncula, they were once placed in the taxon Gephyrea, but it is now clear that they belong toEcdysozoa, which mostly include microscopic animals, with the exception of the

47. priapulida relatively large arthropods, velvet worms, and the priapulids. Their nearest relatives are probably Kinorhyncha and Loricifera with which they constitute the taxonScalidophora.[2] They feed on slow-moving invertebrates, such as polychaete worms. • Priapulid-like fossils are known at least as far back as the Middle Cambrian. They were likely major predators of the Cambrian period. However, crown-group priapulids cannot be recognized until the Carboniferous. Only sixteen extant species of priapulid worms are known.

48.  Priapulid worm Priapulus caudatus in a Petri dish.

49. rotifera • The rotifers (Rotifera, commonly called wheel animals) make up a phylum of microscopic and near-microscopicpseudocoelomateanimals. They were first described by Rev. John Harris in 1696, and other forms were described byAnton van Leeuwenhoek in 1703. Most rotifers are around 0.1–0.5 mm long (although their size can range from 50 μm to over 2 millimeters), and are common in freshwater environments throughout the world with a few saltwater species; for example, those of genus Synchaeta. Some rotifers are free swimming and truly planktonic, others move by inch worming

50. rotifera along a substrate, and some are sessile, living inside tubes or gelatinous holdfasts that are attached to a substrate. About 25 species are colonial , either sessile or plank tonic. Rotifers are an important part of the freshwater zooplankton, being a major food source and with many species also contributing to the decomposition of soil organic matter.[3] Most species of the rotifers are cosmopolitan, but there are also some endemic species, like Cephalodella vittata to Lake Baikal. Recent bar-coding evidence, however, suggests that some 'cosmopolitan' species, such as Brachionus plicatilis, B. calyciflorus, Lecane bulla, among others, are actually species complexes.