Annelida

1. Platyhelminthes Echinodermata Arthropoda Chordata Mollusca Annelida Nematoda Rotifera eucoelomates pseudocoelomates acoelomate

2. protostomes deuterostomes Arthropoda Chordata Echinodermata Mollusca Annelida Platyhelminthes Nematoda Rotifera eucoelomates pseudocoelomates acoelomates

3. Protostome: blastopore becomes the mouth and the anus forms secondarily Future anus blastopore archenteron (primitive gut) mouth

4. Deuterostome: blastopore becomes the anus and the mouth forms secondarily Future mouth blastopore archenteron (primitive gut) anus

5. Protostome: spiral Cleavage 2 cells 4 cells 8 cells Blastomeres divide at an oblique angle to one another, so that each lies in the furrow created by the cells beneath them

6. Deuterostome: Radial Cleavage 2 cells 4 cells 8 cells Blastomeres divide in a symmetrical fashion, producing layers of cells directly on top of one another

7. Protostome: mosaic Development one blastomere is removed development is arrested 4-cell stage

8. Deuterostome: regulative Development One blastomere is removed Development continues Development continues 4-cell stage  each blastomere is capable of regulating its development even when separated from the others

9. Protosome coelom formation: schizocoely ectoderm coelom forms from a split in the mesoderm endoderm mesoderm

10. Deuterostome coelom formation: enterocoely early mesodermal pouch ectoderm coelom forms from an outpocketing of the archenteron endoderm mesoderm

11. Protostome vs Deuterostome Protostome Deuterostome • blastopore becomes the anus • radial / indeterminate cleavage • regulative development • enterocoely • (Echinodermata, Chordata) • blastopore becomes the mouth • spiral / determinate cleavage • mosaic development • schizocoely • (Annelida, Arthropoda, Mollusca, Bryozoa*)

12. Phylum Annelida the segmented worms

13. Annelida Characteristics Triploblastic Organ level of organization Bilateral Symmetry Cephalization

14. Annelida Characteristics Eucoelomate Have a “true” body cavity that is completely surrounded by mesoderm

16. gut gut endoderm endoderm gut

17. Annelid Characteristics the coelom • is a closed, fluid filled cavity that surrounds the gut • the fluid within acts as a circulatory system • mesodermal membranes (mesenteries) suspend organs in the coelom ectoderm

18. Annelida Characteristics Protostome development • blastopore becomes the mouth • spiral / determinate cleavage • mosaic development • schizocoely

19. Annelida Characteristics Body Plan prostomium Metamerism:The body is made up of serially repeating, coordinated segments called metameres that are separated from one another by septa. metameres pygidium

20. septa Each metamere contains sets of repeating organs (e.g. gut, blood vessels, nerve cord, excretory organs)

21. How areproglottids different from true metameres? • Proglottids are not coordinated. • Proglottids only contain reproductive organs.

22. Annelid Characteristics Feeding and Digestion • Free living and parasitic species

23. Annelid Characteristics Digestive System • complete • regional specialization

24. intestine gizzard pharynx crop mouth esophagus

25. Annelida Characteristics Skeletal System • fluid in coelom acts as a hydrostatic skeleton

26. Annelida Characteristics Locomotion • both longitudinal and circular muscles • most have setae (chitonous bristles secreted by the epidermis) that aid in locomotion and burrowing

27. setae epidermis muscles

28. Annelida Characteristics Nervous system • 2 cerebral ganglia • a ventral nerve cord with 2 ganglia per metamere. • In some species, sensory organs such as eyes, palps, and tentacles have arisen

29. segmental nerve cerebral ganglion mouth ventral nerve cord

30. Annelid Characteristics Gas exchange • mainly by diffusion • Some Annelids have specialized structures for gas exchange • (e.g. parapodia, gills)

31. Annelid Characteristics Circulatory System • closed circulatory system composed of blood vessels (some of which are contractile and act as “hearts”) • some circulation is also accomplished by the coelomic fluid

32. subintestinal blood vessel dorsal blood vessel subesophageal blood vessel ventral blood vessel hearts subneural blood vessel

33. Annelid Characteristics Excretion/ osmoregulation • excretion is accomplished by organs called nephridia (singular nephridium) • there are usually 2 nephridia per metamere

34. tubules and capillaries bladder nephridiopores nephrostome

35. protein, water, urea, NH3+, Cl- In nephrostome (from coelomic fluid) uric acid urea NH3+ salts narrow tube middle tube salts protein K+, Na+, Cl- water wide tube bladder water, urea, uric acid, NH3+, Cl- K+, Na+, (out nephridiopore)

36. Annelid Characteristics Reproduction • sexual: monoecious or dioecious • Most species have a trochophore larva

37. Phylum Annelida Class Polychaeta Class Oligochaeta Class Hirudinea

38. Class Polychaeta

39. Class Polychaeta • all marine • this class contains 2/3 of all known Annelids (approx. 10, 000 species) • have a well developed head with specialized sense organs

40. Class Polychaeta • have many setae (chitonous bristles secreted by the epidermis) • (Poly = many, chaeta= setae) • these setae are arranged in bundles on paddle-like appendages called parapodia setae

41. Class Polychaeta notopodium neurodium acicula muscles The parapodia function in gas exchange, locomotion, and feeding. setae

42. capillaries parapodium Lateral blood vessels

43. Class Polychaeta • Tagmatization (tagmosis) • the fusion and specialization of formerly metameric segments

44. Class Polychaeta Many are filter-feeders with specialized structures

45. Class Polychaeta Many are predatory with specialized structures

46. Class Polychaeta Many construct their own homes out of CaCO3 or sand debris and mucous

47. Class Polychaeta • Reproduction • usually dioecious • no permanent sex organs; gametes are shed into coelom • fertilization is usually external • indirect development  trocophore larvae

48. Epitoky Class Polychaeta atoke epitoke

49. Polychaetes often have effective • defense strategies: • some have tubes to hide in • some have vicious jaws • some have modified “stinging” setae Ecology a fireworm

50. Ecology • Some Polychaetes have a mutualistic relationship with their host • for example, many scaleworms are found near, or in the mouth, of brittlestars, starfish, and sea urchins. • The scaleworm eats its host’s leftovers and with its vicious jaws, it will attack any predator trying to eat it’s host.