Transcript Molluscs - Odyssey Expeditions Summer Programs

Mollusks
Odyssey Expeditions
Phylum Molluska
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Means “soft body”
Includes clams, snails, sea slugs, and octopus
Freshwater, marine and terrestrial
Most have external shell of calcium carbonate
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General Characteristics
• Posses a mantle
– Circulates water through
organism
– Feeding, propulsion, and/or
shell production
– Gills or lungs found in
mantle cavity
Radula
• Posses a muscular foot
– Used to crawl with
– Tentacles in cephalopods
• Posses a radula
– Tongue bearing teeth used
for feeding (like a conveyor
belt)
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Classes
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Class Monoplacophora
Class Polyplacophora
Class Aplacophora
Class Gastropoda
Class Bivalvia
Class Scaphopoda
Class Cephalopoda
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Class 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 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 Aplacophora
Ventral View
• Worm-like
• Small (<5mm)
• No shell, have
calcareous spicules
in mantle
• Inhabit deep water
(200 to 7000m)
• Creep or burrow
• Very little known
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Class 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 Subclasses
• Subclass Prosobranchia
• Subclass Opisthobranchia
• Subclass Pulmonata
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Subclass Prosobranchia
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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 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 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 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 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
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NOAA
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Cephalopod Subclasses
• Subclass Nautiloidea
• Subclass Ammonidea
• Subclass Coleoidea
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Subclass 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 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 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
Jason Buchheim
NOAA
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Resources
• 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
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