Ch 27: Molluscs and Annelids

1. Ch 27: Molluscs and Annelids There are some things on the review sheet and test that you should add to this presentation – eg – mussels have special glue

2. Phylum Mollusca

3. Molluscs – Characteristics that Unify • Have true coelom • Are protostomes • Have trochophore larvae (like annelids) • Have foot, mantle, visceral mass, and possibly a shell

4. Protostomes, Coelomates

5. Trochophore larvae • Molluscs and Annelids – a common ancestor?

6. Internal Structures of Molluscs • Foot – structure involved in feeding, usually contains the head as well • Visceral mass – contains the internal organs • Mantle – secretes the shell • Shell - protection

7. Molluscs – classified by the modifications of the Foot • Gastropods – “stomach foot” • Foot is broad and muscular • found along the ventral surface • used for moving, eating • Examples: Snails, slugs, nudibranchs

8. Class Gastropoda - Snails

9. Snail Diagram

10. Gastropods - Sea slugs/nudibranchs

11. Cephalopod – the tentacled molluscs • “Head –foot” • Foot is modified into head with tentacles coming out of it • Have very little shell if any • Ex. Octopi, squid, nautilus, cuttlefish, • Cephalopod – the tentacled molluscs

12. Cephalopods havea ‘head’

13. Cephalopods include: • Octopi Have internal shells • Squid Swim with jet propulsion • Cuttlefish • Nautiluses

14. Bivalves • Have 2 shells – foot can extend out of shell • Clams, mussels, oysters

15. Class Bivalvia • 2 shells • Clams • Oysters • Mussels

16. Typical Shell/Valve

17. Feeding - Molluscs • Many molluscs have a structure that is like a very rough tongue – has hundreds of tiny teeth for grinding through shells or scraping algae off of rocks

19. Molluscs – Filter feeders • filter feeders use their GILLS to catch the tiny food particles • They also use the gills to BREATHE

20. Filter Feeders – Environmental “Watchdogs” • Filter feeders remove the pollutants from the water and concentrate them in their bodies • Environmentalists can use these animals to learn information about levels of pollution in the water.

21. Don’t eat bivalves during a RED TIDE

22. Red Tide

23. Clam – How it eats • Incurrent siphon pulls water across gills • Food particles stick to gills • Coordinated cilia move food to mouth • Food is stored/digested in stomach and intestines • Solid wastes exit via the anus

24. Respiration - Molluscs • Aquatic molluscs use gills • Land snails and slugs use a moist sac inside the mantle • Sac’s lining is convoluted (to increase surface area) and lined with blood vessels

25. Molluscs Circulatory Systems • Marine snails, slugs, clams: Slow-moving molluscs have “open” circulatory systems (like some insects) • Blood vessels connect to sinuses where oxygen transfer takes place • Octopi, squid: Fast-moving molluscs have “closed” circulatory systems – blood is completely enclosed in blood vessels (like ours)

26. Circulatory System Comparisons

27. Excretion – Molluscs and Annelids • Molluscs and annelids are coelomates and protostomes – that means they definitely have an anus for solid wastes! - they use NEPHRIDIA for metabolic wastes (like the nephrons in our kidneys

28. Nervous Systems -Molluscs • Slow moving molluscs have simple systems with simple sensory cells like the cnidarians and the worms – statocysts, ocelli, chemoreceptors, touch receptors, etc. Scallop 

29. Nervous Systems - Molluscs • Fast-moving molluscs have very complex nervous systems Octopi: • Well-developed brain (with memory) • Eyes that are similar to ours – form images

30. Reproduction - Molluscs • MOST have separate sexes that employ external fertilization (fertilization by chance!) • Tentacled molluscs and some snails have internal fertilization • Some are hermaphrodites

31. Molluscs - reproduction • Oysters – hermaphrodites that change sexes each season – sometimes they are the males, sometimes the females.

32. Defence Mechanisms - Gastropods • Slugs hide under rocks or only come out at night • Some gastropods are poisonous – brightly colored to warn off predators • Some nudibranchs save the nematocysts from the cnidarians they ate, and sting their predators with them

33. Poisonous !

34. Cephalopods – Defence Mechanisms • Octopi move rapidly backwards with their jet propulsion of water • Some release foul-tasting black ink • Some can change colours

36. Squid – 8 arms + 2 long tentacles

37. Annelids – Characteristics that unify • Segmented worms • Coelomates • Trochophore larvae • protostome

38. Segmentation

39. Annelids – Feeding • Filter feeders – use gills to capture food particles from water • Others use pharynx to either suck in food or to extend out and get it. • Some annelids have jaws on their pharnyx • Christmas tree worm 

40. Nereis – (clam worm) A Polychaete – has jaws for eating and fighting

41. Respiration Earthworm cuticle  • Aquatic annelids use gills • Terrestrial annelids exchange gases through their skin – their skin must remain moist for this purpose • Cuticle on the earthworm helps prevent desiccation Feather-duster worm – gills exposed (red) - tentacles for gathering food

42. Internal Transport • Closed circulatory system • Dorsal surface has blood moving toward the head, ventral surface moves blood away from the head • Each segment has a ring vessel connecting the ventral with the dorsal • Large ring vessels at anterior end act as a “heart” to pump the blood • If no heart is present, the bodies muscular contractions move the blood around

43. Excretion • Solid wastes out the anus • Metabolic (liquid) wastes are eliminated by nephridia (like the nephrons in our kidneys) • 2 nephridia/segment

44. Response • Brain on dorsal surface • Nerves travel from the brain, around the gut and a main nerve cord travels down the ventral surface Brain = #11 Ganglia = #12 Ventral Nerve cord = #13

45. Sense organs • Best developed in free living annelids • Most of these have sensory tentacles, statocysts, chemoreceptors, and “eyes” • Some form images, some are light-detectors • Some have sensory organs that detect vibrations (like our tympanic membranes) Spaghetti worm underground With tentacles exposed

46. Self Defence • Burrow into ground or swim away • Setae (one-way bristles) anchor worms in the soil • Marine fan worms make tubes of CaCO3 to hide in Tube worms 

47. Self-Defence • Marine fireworms have poisonous bristles (burns) • Carnivorous annelids have jaws to bite their predators

48. Movement • longitudinal muscles shorten the body • Circular muscles contract to decrease the diameter of the worm • Coordination of these sets of muscles allow the worms to wiggle, burrow and swim

49. Reproduction • Some reproduce by budding • Some have separate sexes and have external fertilization • Palolo worms congregate at the surface and release sperm or eggs at the same time • Feast for the predators (humans included!)