27.3 Annelids

1. 27.3 Annelids Essential Question What is an annelid?

2. What is an Annelid? • Worms with segmented bodies. • Specialized segments contain sense organs, and carry out respiration • Separated by septa • Bristles called setae attached to each segment • True coelom lined with mesoderm • Tube-within-a-tube digestive system that passes food from the mouth to the anus.

3. How do annelids eat and digest food? • Get food using pharynx • Some are predators • get food from pharynx that holds sharp jaws used to attach prey • Some are filter feeders • Fan water through tube-like burrows and catch food particles in a mucous bag • Some feed on decaying vegetation • In earthworms, the pharynx pumps food and soil into the esophagus, where it moves into the crop (stored), and through the gizzard where it is ground into smaller pieces.

4. Circulation • closed circulatory system in which blood is contained within a network of blood vessels. • Blood circulates through two major blood vessels that run head to tail • Each body segment has a pair of smaller blood vessels that connect dorsal to ventral blood vessels and supply blood to internal organs • Dorsal blood vessel acts like a heart because it contracts and helps to pump blood

5. Respiration • Aquatic annelids breath through gills • Land-dwelling worms breath through skin secreting a thin coating of mucus keeping skin moist

6. Excretion • Produce two kinds of waste • Digestive waste passes out through the anus at the end of the digestive tract • Cellular waste containing nitrogen are eliminated by nephridia (excretory organs)

7. Response to Environment • Most have well developed nervous system consisting of brain and several nerve cords • Best developed in marine annelids • Tentacles • Chemical receptors • Statocysts • Two or more pairs of eyes

8. How do annelids move? • two major groups of body muscles that function as part of a hydrostatic skeleton • Longitudinal muscles run from the front to the rear and contract to make the worm shorter and fatter • Circular muscles warp around each body segment and contract to make the worm longer and thinner. • The earthworm moves by alternately contracting these two sets of muscles.

9. Reproduction • Reproduce sexually • Some species use external fertilization and have separate sexes • Earthworms are hermaphrodites, however individual worms rarely fertilize their own eggs. • Two worms attach, attach and exchange sperm and store in special sacs • When eggs are ready for fertilization, clitellum secretes a mucus ring into which eggs and sperm are released.

10. Cont’d • Fertilization takes place with in this ring. • Ring slips off and forms protective cocoon and young worms hatch weeks later

11. Comparison of three types of body cavities studied so far. Body cavities

12. Respiration • Aquatic annelids often breath through gills. • Land-dwelling worms take in oxygen and give off carbon dioxide through their moist skin • They secrete mucus to keep skin moist.

13. Response • well developed nervous systems consisting of brain and several nerve cords. • Many have adaptations to detect stimuli such as sensory tentacles, chemical receptors, statocysts (detect gravity) and two or more pairs of eyes.

14. 3 Classes of Annelids • Oligochaeta – earthworms • Hirudinea – leeches • Polychaeta – polychaetes (sandworms, bloodworms)

15. Oligochaetes • Class: Oligochaeta • Examples are earthworms • streamlined bodies and few setae • most live in soil or fresh water. • most live in soil or fresh water. • When the worm swallows, a mixture of detritus and soil passes through its system. • Any undigested matter passes out as castings.

16. The Anatomy of an Earthworm Anus Setae Body segments Dorsalblood vessel Gizzard Crop Clitellum Mouth Brain Ganglion Circular muscle Ventralblood vessel Ringvessels Reproductiveorgans Ganglia Nephridia Longitudinalmuscle Section 27-3

17. Earthworm gathering

18. Calcerous tubes of marine annelids

19. Leeches • Hirudinea • Contains leeches • Live in tropical habitats • External parasites that suck blood from their host using suckers that attach to body • used in old days to cure diseases – though to suck out disease

20. Segmentation evident Suction disk Leech

21. Leech

22. Leech 3 pairs of eyes

23. Polychaetes • Class Polychaeta • Contains sandworms, bloodworms, and relatives • Marine annelids that have paired, paddle-like appendages tipped with setae • Live in cracks and crevices in coral reefs, in sand, mud, piles of rocks.

24. WOW ! lots of variety and color in marine species

25. Marine polycheate – bristle worm

26. Bristle worms

27. Ciliated feathery tentacles for Feeding tube Marine fanworm

28. Feather duster worms ( Polychaetes) Filter feeder

29. Feather Duster worms

30. Giant tube worms ( 4 ft long) in ocean thermal vents

32. Ecology of Annelids • Tunnels provide passageways for plant roots and allow for the growth of beneficial bacteria. • Pull plant matter down into soil and pass it through their gut, mixing with bacteria and allowing it to decompose • Mine minerals from deeper soil layers bringing it up to surface • Castings (feces) are rich in nitrogen, phosphorous, potassium, micronutrients, and bacteria • Part of many animals food chains on land and in ocean