Annelids

1. Annelids

2. Annelids • Phylum Annelida – “little ring” – segmented body • Round worm-like animal that has a long, segmented body • Sizes range from .5mm to 3m • True coelom lined with mesoderm • “tube-within-a-tube” digestive tract – mouth to anus • Segments separated by internal walls celled septa. Most segments are identical, some modified

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

4. Anatomy of an Earthworm

5. Feeding in Annelids • Filter feeders to predators • Pharynx – very muscular, may be armed with jaws (predators and herbivores), may be sticky (mucus, detritus feeders), act like a pump (deposit feeders and parasites) • Mucus bag – filter feeders • Feather-like structures – filter feeders • Pharynx – esophagus – crop (storage) – gizzard (ground up) – intestine

6. Circulation in Annelids • Closed circulatory system – blood contained within blood vessels • Blood moves toward the head (dorsal vessel) • Blood moves away from the head (ventral vessel) • Ring vessels in each segment connect dorsal to ventral vessels • Vessels act as “hearts” which help pump blood through the system

7. Respiration in Annelids • Gills – aquatic • Skin – must stay moist, secrete cuticle (earthworm)

8. Excretion in Annelids • Solid wastes pass through the anus • Waste from cellular metabolism eliminated by nephridia

9. Response in Annelids • Brain and several nerve cords • Ventral nerve runs entire length of body • Sense organs most often found in polychaetes • True eyes that see shapes, Statocysts, chemical receptors, sensory tentacles, vibration sensors • Defense, runaway and hide, a few fight with jaws (sandworm) • Marine fireworms have irritating bristles

10. Movement in Annelids • Muscles • Longitudinal – lengthwise – make worm longer and shorter • Circular – make worm fatter and skinnier

11. Reproduction in Annelids • Most reproduce sexually • External (broadcast) spawners – worms swarm to surface to spawn by millions • Some hermaphrodites – exchange sperm; clitellum secretes mucus ring containing eggs and sperm which forms cocoon (earthworm)

12. Groups of Annelids • Three classes of Annelids • Class Oligochaete • Class Polychaete • Class Hirudinea

13. Class Oligochaetes • Few “bristles” – few setae • Earthworms and tubifex worms • Deposit feeders, eat dirt and produce “castings” – aerate and fertilize the soil • Tropical earthworms produce castings 18cm long and 2cm in diameter • Soil or freshwater

14. Examples of Class Oligochaetes

15. Class Polychaetes • Many “bristles” • Paired, paddle-like, appendages tipped with bristles (setae) (sea mouse) • Live in all sorts of marine habitats • Some free-living, some tube-builders • May be brightly colored, iridescent, or luminescent

16. Examples of Class Polychaetes

17. Class Hirudinea • Most parasitic, some carnivorous, most freshwater • 6cm to 30cm long, two suckers, one at each end • Penetrate skin by use of proboscis or sharp jaws • Produce secretions that prevent clotting and anesthetizes wound • Can swallow ten times its weight

18. Examples of Class Hirudinea

19. Comparing Flatworms, Roundworms, and Annelids CHARACTERISTIC Shape Segmentation Body cavity Digestion and excretion Respiration FLATWORMS Flattened No Acoelomate Gastrovascular cavity with one opening only; flame cells remove metabolic wastes Through skin; no respiratory organs ROUNDWORMS Cylindrical with tapering ends No Pseudocoelomate Tube-within-a-tube digestive tract; opening at each end; metabolic wastes excreted through body wall Through skin; no respiratory organs ANNELIDS Cylindrical with tapering ends Yes Coelomate Tube-within-a-tube digestive tract; opening at each end; nephridia remove metabolic wastes Through skin; aquatic annelids breathe through gills

20. Comparing Flatworms, Roundworms, and Annelids (Continued) CHARACTERISTIC Circulation Response Movement Reproduction FLATWORMS No heart, blood vessels,or blood Simple brain; nerve cords run length of body; eyespot and other specialized cells that detect stimuli Gliding, twisting,and turning Sexual (hermaphrodites); asexual (fission) ROUNDWORMS No heart, blood vessels,or blood Several ganglia in head region; nerve cords run length of body; several types of sense organs Thrashing Sexual (primary males and females) ANNELIDS Blood circulated through blood vessels in closed circulatory system Well-developed nervous system with brain and several nerve cords; many sense organs Forward peristaltic movement Sexual (some are hermaphrodites; some have separate sexes)

21. Mollusks

22. Phylum Mollusca • Phylum Mollusca • 100,000 species • Most share trocophor larval stage (free-swimming larval stage) • Defined as soft-bodied animals that have an internal or external shell

23. Coelom Stomach Heart Shell Nephridium Adductor muscle Mouth Anus Excurrentsiphon Adductormuscle Incurrentsiphon Gills Mantle cavity Intestine Mantle cavity Foot Anatomy of a Clam

24. Form and Function in Mollusks • Body Plan – four parts: mantle, foot, shell, visceral mass • Mantle – thin layer of tissue that covers most of the mollusk body – contains shell glands • Foot – movement, mouth, and associated feeding structures • Shell – protection • Visceral mass – contains all organs

25. The Mollusk Body Plan Squid Snail Shell Mantle cavity Foot Gills Digestive tract Clam Earlymollusk

26. Feeding in Mollusks • Herbivores, carnivores, or filter feeders • Radula – found in snails and slugs – rasp-like tongue • Herbivores scrape food • Predators drill shells or “dart” food • Cephalopods – beaks • Clams, oysters, scallops – filter feeders use gills • Octopi use siphon (tube-like structure) to trap plankton

27. Respiration in Mollusks • Gills in mantle cavity in aquatic species • Modified mantle in terrestrial species

28. Circulation in Mollusks • Open circulatory system – blood flows through vessels and “sinuses” (open spaces) (clams and snails) • Closed circulatory system – blood always flows inside vessels (cephalopods)

29. Excretion in Mollusks • Remove ammonia with use of tube-shaped organs called nephridia

30. Response in Mollusks • Simple to very complex nervous systems (scallops, octopi) • Cephalopods, highly evolved eyes and brains

31. Movement in Mollusks • Mucus in snails and slugs • Jet propulsion in octopi

32. Reproduction in Mollusks • In most mollusks, sexes are separate, broadcast spawners • Cephalopods, internal fertilization • Some gastropods are hermaphroditic

33. Groups of Mollusks • Three classes of mollusks • Class Gastropoda • Class Bivalvia • Class Cephalopoda

34. Class Gastropoda • “stomach foot” • Snails, slugs, abalones, nudibranchs • Some snails have operculum (hard disk on foot that forms a “door” when inside shell) • Nudibranchs feed on cnidarians; utilize nematocysts for their own defense • Bright colors mean bad taste or even poison

35. Examples of Class Gastropoda

36. Class Bivalvia • “two shell” • Clams, oysters, scallops • Most are sessile • Epifaunal – on top of bottom (oyster, mussels) • Infaunal – in bottom (clams) • Some are motile – scallops can move by flapping shells and have eyespots (Ocelli)

37. Scallop Swimming

38. Examples of Class Bivalvia

39. Class Cephalopoda • “head foot” • Squid, octopus, cuttlefish, nautilus • Predators, beak for mouth • Seem to be intelligent • Move quickly via jet propulsion • Little or no shell • Highly developed eyes and brains

40. Examples of Class Cephalopoda

41. Ecology of Mollusks • Fried calamari • Shipworms • aquaculture

42. Comparing the Three Major Groups of Mollusks MOLLUSK GROUP Gastropods Bivalves Cephalopods SHELL Shell-less orsingle-shelled Two shells held together by oneor two muscles Internal shell orno shell FOOT Muscular foot located on ventral side and used for movement Burrowing species have muscular foot. Surface-dwelling species have either no foot or a “reduced” foot. Head is attached to a single foot. The foot is divided into tentacles or arms. EXAMPLES Snail, slug, sea hare, nudibranch Clam, oyster, mussel, scallop Octopus, squid, cuttlefish, nautilus