1. Mollusks Squishy Squad

2. Categories Gastropoda (ex: snail) Bivalvia (ex: clam) Cephalopoda (ex: squid) Schaphopoda Monoplacophora Polyplacophora Aplacophora Caudofoveta

3. Evolution There are fewer cephalopods now. –Only 550 species –Vertebrate competition? Overall, Mollusks are very successful. –Over 100,000 species –Gastropoda –Bivalvia Triploblastic, coelomic

4. Characteristics 1 2 part body: head-foot, visceral mass Mantle secretes shell, covers visceral mass Mantle cavity – excretion, gas exchange, elimination, release of gametes Bilateral symmetry

5. Characteristics 2 Trochophore larvae, spiral cleavage, schizocoelous coelom formation Coelom surrounds heart, nephridia, and gonads Mostly open circulatory system (not in cephalopoda) Radula used in scraping food

6. Body plan – head-foot Anterior head –Mouth –Nervous structures –Sensory structures Foot –Attachment –Locomotion

7. Body plan – visceral mass Contains organs for –Digestion –Circulation –Reproduction –Excretion Dorsal to head-foot

8. Body plan – mantle Outer layer Attaches to visceral mass May secrete a shell (3 layers) Mantle cavity (excretion, gas exchange, elimination, release of gametes)

9. Body plan - radula Row of teeth on a chitinous belt –Sits on odontophore (tongue) –Moves back and forth to bring food in

10. Gastropods Limpets and Snails and Slugs Oh my!

11. A large class 35,000 living species Marine, freshwater, and terrestrial Helix pomatia Garden snails Int. host of human parasites

12. Torsion Occurs in early development 180° twisting of VM, mantle, and mantle cavity Moves gills, anus, & openings from excretory and rep. systems just behind the head

13. Torsion Plausible advantages 1.Head enters shell 1st –Some have operculum 2.Clean water enters mantle cavity 3.Sensory organs in front

14. Waste exits above head? Evolutionary adaptations –Waste exits through notches behind head –Detorsion Twist 180° Untwist 90° Waste exits to side, behind head

15. Shell coiling Earliest fossils coiled in one plane Most modern snails like the one at the bottom right –Less room at tight end –Paired organs  single organs

16. Locomotion Crawling –Cilia –Muscular waves (bonus snail)Muscular wavesbonus snail Modified foot for clingingfoot Swimming (sea butterfly & sea hare)sea butterfly sea hare

17. Feeding Scrape algae using radula Herbivores Scavengers Parasites Predators (whelk proboscis)whelk proboscis

18. Digestion Tract is ciliated Food trapped in mucus strings Protostyle - mucus mass in stomach Digestive enzymes Wastes as fecal pellets

19. Respiration Always involves mantle cavity Modern orgs have one gill Some have a siphon –Inhalant tube –Burrowers extend it up Gills lost or reduced in land orgs

20. Open Circulatory System Leaves the vessels Enters sinuses to bathe cells Heart w/single auricle and ventricle Blood acts as hydraulic skeleton –Move blood to move body –Retract quickly, expand slowly

21. Nervous System Eyes – base on top or bottom of tentacle –Simple pit of photoreceptors –Lens and cornea Statocysts on foot Ophradia – chemoreceptors –Detect sediment –Detect prey

27. The other classes Caudofoveta Solenogastres Monoplacophora Polyplacophora Schaphopoda

28. Caudofoveata 120 worm-like species Marine 2 - 140 mm in length Orient vertically in sand Gills pointed up

29. Caudofoveata Feeding –Feed on microorganisms and detritus (dead stuff) –Oral shield and radula for food intake One pair of gills

30. Caudofoveata Dioecious –Sexual reproduction –Fertilized eggs are brooded –Larvae swim freely

31. Solenogastres 250 species of marine animals Similar to caudofoveata BUT!!! –No radula –No gills Bottom dwellers Feed on cnidarians

32. Monoplacophora Once thought extinct 1952 – Neopilina found 25 species now known Small w/ low, rounded shell Mouth has radula Look like limpets

33. Monoplacophora Unlike other mollusks – repeating organs –3 to 6 pairs of gills –2 pairs of auricles –3 to 7 pairs of metanephridia –1 to 2 pairs of gonads –10 pairs of pedal nerves

34. Polyplacophora Chitons (many plate bearers, Coat of mail) 1000 species Most 2-5 cm, largest 30 cm

35. Polyplacophora Dorsoventrally flattened Convex dorsal surface w/7-8 limy plates or valves Esthetes – photosensitive

36. Polyplacophora Blend in w/rocks Homebodies Can roll up like an armadillo

37. Polyplacophora Mantle cavity is tube-like Closes at low tide Some can breathe air 3 chambered heart Pair of metanephridia 2 pairs of longitudinal nerve cords Dioecious

38. Scaphopoda Tusk shells or tooth shells From subtidal zone to 6000 m deep 900 species Most are 2.5-5 cm range from 4-25 mm

39. Scaphopoda Mantle wrapped around VM Shell open at both ends –Foot at wider end –Burrows into sand or mud –Leaves small end exposed

40. Scaphopoda Water circulates via foot and cilia movements No gills (gas exchange occurs in mantle)

41. Scaphopoda Food –Detritus & protozoa from substratum –Caught on cilia on foot OR –Ciliated adhesive knobs on tentacles (captacula) Extend from head Food carried to head From radula to gizzard

42. Scaphopoda No tentacles, eyes, or osphradia Dioecious