Mollusks Odyssey Expeditions. 2 Phylum Molluska Means “soft body” Includes clams, snails, sea slugs, and octopus Freshwater, marine and terrestrial Most.

MollusksMollusks

Odyssey ExpeditionsOdyssey Expeditions

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Phylum MolluskaPhylum Molluska

• Means “soft body”• Includes clams, snails, sea slugs, and octopus• Freshwater, marine and terrestrial• Most have external shell of calcium carbonate

Jason Buchheim

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General CharacteristicsGeneral Characteristics• Posses a mantle

– Circulates water through organism– Feeding, propulsion, and/or shell

production– Gills or lungs found in mantle

cavity

• Posses a muscular foot– Used to crawl with– Tentacles in cephalopods

• Posses a radula– Tongue bearing teeth used for

feeding (like a conveyor belt)

Radula

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ClassesClasses

• Class Monoplacophora

• Class Polyplacophora

• Class Aplacophora

• Class Gastropoda

• Class Bivalvia

• Class Scaphopoda

• Class Cephalopoda

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Class MonoplacophoraClass Monoplacophora

• Relic class• Many fossilized mollusks

belong to this class • Less than 20 extant

(living) species• Single cap-like shell• Creeping foot• Found in deep water

(2000 to 7000m)

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Class PolyplacophoraClass Polyplacophora

• Chitons• Oval in shape• Eight over lapping plates• Creeping foot that

adheres tightly to rocky surfaces

• Mostly inhabit rocky intertidal zones

• Feed on algae and other organisms on the rocks

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Class AplacophoraClass Aplacophora

• Worm-like• Small (<5mm)• No shell, have

calcareous spicules in mantle

• Inhabit deep water (200 to 7000m)

• Creep or burrow• Very little known

Ventral View

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Class GastropodaClass Gastropoda• Largest class of mollusks

(30,000 species)• Snails and snail-like

organisms• Well developed head

with tentacles and eyes• Most possess single

coiled asymmetrical shell• Most crawl with foot but

some swim with it

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Gastropod SubclassesGastropod Subclasses

• Subclass Prosobranchia

• Subclass Opisthobranchia

• Subclass Pulmonata

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Subclass ProsobranchiaSubclass Prosobranchia• Mantle cavity anterior • Marine• Shelled• Many have operculum

(hard disc attached to the foot that covers the opening to the shell for protection)

• Some use mantle as camouflage

• Includes conchs, whelks, cones, abalone, and drills

• Herbivores and carnivores

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Subclass OpisthobranchiaSubclass Opisthobranchia

• Mostly marine• Shell reduced or lacking• Mantle cavity on right side, posterior,

or even lacking• Some respire through skin or external

gills• Mantle generally colorful and ornate• May have modified foot to swim with• Typically few inches in length • Includes sea hares, nudibranchs, sea

slugs• Herbivores and carnivores (have very

specific diets)

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Subclass Pulmonata

• Typically terrestrial• Shelled (except

slugs)• Mantle cavity

modified into lungs• Includes terrestrial

snails, freshwater snails and slugs

• Typically herbivores

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Class BivalviaClass Bivalvia• Consists of two hinged shells or valves• Gills used for filter feeding as well as

respiration (water brought in and out by siphons while buried in sediment)

• The mantle of some contains tentacles and eye spots to detect movement.

• No head• Second largest molluscan class (8,000

extant species)• Freshwater and marine• Includes cockles, mussels, oysters,

scallops, and clams

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Class ScaphopodaClass Scaphopoda• Tusk or tooth shell (looks like

elephant’s trunk)• Marine• Single elongated tube-like

shell.• Burrowing• Modified foot for digging • Possess tentacles to capture

interstitial (organisms found among sediment grains)

• 2-6 cm long

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Class CephalopodaClass Cephalopoda• Elongated• Highly cephalized• Well developed nervous

system• Foot modified into

specialized arms and tentacles for prey capture

• Shell external, internal, or absent

• Includes nautilus, squid, octopus, and cuttlefish

• Propulsion created by expulsion of water from mantle cavity

NOAA

Jason Buchheim

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Cephalopod SubclassesCephalopod Subclasses

• Subclass Nautiloidea

• Subclass Ammonidea

• Subclass Coleoidea

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Subclass NautiloideaSubclass Nautiloidea• Nautilus• Only 4 extant species

(most are extinct)• Multi-chambered

external shell• Gas in chambers

provides buoyancy (connected by central siphuncle canal and separated by septa)

• Siphuncle used to add or remove gas to chambers

• Many arms (~90) for prey capture

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Subclass AmmonideaSubclass Ammonidea

• All members extinct

• Coiled, external, multi-chambered shells

• Complex septa with siphuncle found along outer axis of shell

• Index fossils

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Subclass ColeoideaSubclass Coleoidea• Squid, octopus,

cuttlefish• Internal or lacking shell• Eight arms with

suckers• Squid and cuttlefish

also have two tentacles for prey capture

• Ability to camouflage is exceptional

• Have large nerve cells used in research

NOAA

Jason Buchheim

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ResourcesResources

• Barnes, Robert D. and Edward Ruppert. Invertebrate Zoology: Sixth Edition. Fort Worth: Saunders College Publishing, 1994

• Humann, Paul and Ned Deloach. Reef Creature Identification: Florida Caribbean Bahamas. Florida: New World Publications, Inc., 2003

• Kinsella, John, Drew Richardson and Bob Wohlers. Life on an Ocean Planet. California: Current Publishing Corp., 2006

• Taylor, Walter K. and Robert L. Wallace. Invertebrate Zoology: A Laboratory Manual Sixth Edition. New Jersey: Prentice Hall, 2002