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Class Gastropoda Snails - largest class of molluscs

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1 Class Gastropoda Snails - largest class of molluscs
~ 85,000 living spp. ~ 15,000 fossil spp. Habitats: marine benthos, ocean plankton, freshwater, land

2 Gastropod characteristics
1. Torsion - primitive bilateral symmetry lost during development Twisting of visceral mass, mantle, and mantle cavity After torsion

3 Gastropod characteristics
2. Definite head: eyes, tentacles 3. Flat ventral foot 4. Mantle cavity w/gills or lungs 5. Buccal cavity w/ radula

4 Characters cont. 6. Coiled shell - one continuous piece
operculum on posterior foot of some plano-spiral helico-spiral

5 Characters, cont. 7. Centralized complex nervous system
8. Hermaphroditic or dioecious 9. Oviparous or ovoviparous

6 10. Larval form Archaeogastropoda have trochophore larva
Many marine snails have veliger larva Freshwater + terrestrial species usually hatch as young snails

7 Gastropod classification
3 subclasses: Prosobranchia Opisthobranchi - reduced shell Pulmonata - lungs

8 Subclass Prosobranchia
Mantle cavity anterior 1 or 2 gills shell and operculum usually present most are dioecious

9 Prosobranchs, Order Archaeogastropoda
Primitive snails External fertilization Trochophore larva 2 bipectinate gills 2 auricles 2 coelomoducts

10 Prosobranchs, Order Archaeogastropoda
A. slit shells - deep water species Abalones (Haliotis) 9 spp on our Pacific coast Commercially harvested

11 Prosobranchs, Order Archaeogastropoda
B. keyhole limpets - Fissurella conical shells C. Limpets - Acmaea

12 Prosobranchs, Order Archaeogastropoda
D. topshells, turban shells, star shells Astraea

13 Prosobranchs, Order Archaeogastropoda
E. Nerites (Nerita) intertidal in Caribbean some freshwater + terrestrial

14 Prosobranchs, Order Mesogastropoda
Male with penis Fertilization internal 1 monopectinate gill 1 auricle 1 coeloduct

15 Prosobranchs, Order Mesogastropoda
A. Freshwater apple snails - Viviparus, Pomacea

16 Prosobranchs, Order Mesogastropoda
B. Turret shells - worm shells; caecums, ceriths, some freshwater genera, all have high shells

17 Prosobranchs, Order Mesogastropoda
C. Violet snails - pelagic grazers on man o’war Vellela, Porpita Janthina: secretes bubble mass for floatation

18 Prosobranchs, Order Mesogastropoda
D. Cap shells, slipper shells Crepidula change sex w/age see slides of veliger larva

19 Prosobranchs, Order Mesogastropoda
E. Conchs - Strombus Feed on algae, turtlegrass Commercial harvest in Caribbean

20 Prosobranchs, Order Mesogastropoda
F. Cowries; Cypraea - graze on algae, sponges, gorgonians, and tunicates Mantle covers most of shell when extended Favorites of shell-collectors No periostracum Italians call them “porcellanos” = little pigs Porcelain got its name

21 Cowries

22 Prosobranchs, Order Mesogastropoda
G. Heteropods - pelagic, swimming snails w/reduced shell Carinaria (see Fig , p. 399) Heteropod Snail, Carinaria. Heteropods are predators. The head is on the right with the mouth at the tip. The pink area contains the radula. The two dark spots a bit back are the eyes with the whitish brain in between. The digestive tract extends back from the radula region, dilates behind the eyes, and continues on to the stomach surrounding a brown mass, the digestive gland. A thin shell surrounds the digestive gland and is heavy enough to make the animal swim upside down. The vertral foot shows as a mass oriented upward on the upside.

23 Prosobranchs, Order Mesogastropoda
H. Moon shells - predators on molluscs: bore into shells Lunatia Polinices

24 Moon shells: Muscular suction disk holds snail on clam shell
Drill through shell with radula: Wiggle proboscis into flesh Remove most of flesh from clam

25 Prosobranchs, Order Mesogastropoda
I. Helmet shells, tritons, tuns Predators on molluscs and echinoderms Long proboscis Large shells

26 Prosobranchs, Order Mesogastropoda
J. Periwinkles - intertidal Littorina

27 Prosobranchs, Order Neogastropoda
Mostly same characteristics as Mesogastropoda Radula has only 3 teeth in a transverse row Most are marine Most are carnivores

28 Prosobranchs, Order Neogastropoda
A. Drills - Murex, Urosalpinx Drill holes in shells of bivalves and barnacles Oyster drill and others cause economic losses

29 Prosobranchs, Order Neogastropoda
B. Whelks - Busycon Tulip shells - Fasciolaria Predators and carrion feeders

30 Prosobranchs, Order Neogastropoda
C. Olives, miters, and volutes Colorful, mostly tropical snails prey on invertebrates

31 Prosobranchs, Order Neogastropoda
D. Cones - Conus Most prey on inverts Those that prey on fish can be dangerous to humans Fig 10-42, p. 409

32 Conus Long proboscis with harpoon-like radular tooth venom gland

33 “Glory of the sea” cone shell

34 Subclass Opisthobranchia
Detorsion - brings mantle cavity to right side 1 gill, 1 auricle, 1 coelomoduct Shell often reduced or absent Mantle cavity often reduced or absent Many are secondarily bilateral symmetric Hermaphroditic

35 Subclass Opisthobranchia
A. Bubble shells - Bulla Predators with thin, reduced shell

36 Subclass Opisthobranchia
B. Sea hares - Aplysia Thin, caplike shell overgrown by mantle Vegetarians (herbivores) Can eject milky fluid from mantle cavity A. californica has largest body of all gastropods

37 Subclass Opisthobranchia
C. Sea slugs With or w/o shell Berthelinia is a “bivalve” gastropod Fig , p. 392

38 Subclass Opisthobranchia
D. Pteropods or sea butterflies 2 orders with and w/o (naked) shells Planktonic with foot modified into wing-like flaps for swimming Often occur in enormous numbers

39 More Pteropods

40 Subclass Opisthobranchia
E. Nudibranchs Often with secondary gills and cerata (hornlike dorsal projections) Many endemics

41 Subclass Opisthobranchia
F. Parasitic Opisthobranchs 2 orders One ectoparisitic on bivalves and annelids One endoparasitic in sea cucumbers

42 Subclass Pulmonata Charactistics like Opisthobranchia, but w/o gill
Mantle cavity converted to lung Shell usually present No operculum Hermaphroditic

43 Subclass Pulmonata A. freshwater snails: Most come to surface for air
Lymnaea, Physa, Planorbis Freshwater limpets Most come to surface for air Some have developed secondary gills Descended from terrestrial ancestors

44 Subclass Pulmonata B. Land snails and slugs
Helix Limax C. Intertidal slugs w/posterior anus

45 Class Scaphopoda tusk shells
~ 300 spp. Sedentary, marine burrowing, in m depth Shells resemble elephant tusks Most burrow in sand, few in mud Feed on microscopic organisms; foraminiferans Considered offshoot of early bivalve ancestors

46 Scaphopod characteristics
1. Tusk-like shell open at both ends 2. Bilateral symmetry (like bivalves) 3. Rudimentary head no eyes Head has threadlike, food gathering tentacles (captacula)

47 Foot

48 Scaphopod characteristics
4. Radula present 5. Circulatory system reduced - sinuses Gills absent 6. Dioecious, trochophore and veliger larval stages

49 Scaphopod classification
Two families (representative species): Dentalium - conical shell Cadulus + Siphonodentalium - globular shell, enlarged foot

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