Transcript PHYLUM MOLLUSCA - G. Holmes Braddock High School

PHYLUM MOLLUSCA
CLAMS,SQUIDS, OCTOPUSES,
SNAILS, SLUGS, ETC.
General Characteristics
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More than 100,000 species
“soft bodied”
Bilaterally symetrical
Trochophore larva
3 main body parts
– Mantle: thin membrane that surrounds the visceral
mass, and secretes shell
– Visceral mass: digestion, excretion, and
reproductive organs
– Head-foot: sense organs, mouth, and is used for
locomotion
5 Major Classes of Mollusks
• Class Amphineura (Polyplacophora) –
Chitons
– 8 calcareous plates on their dorsal surface
– Feed by grazing on algae along rocky intertidal
zones
• Class Scaphopoda – Tusk Shells
– Elongated shell open at both ends that resemble
elephant tusks
– Live in sandy or muddy bottoms
– Feed by extending tentacles into surrounding
sediment or water
• Class Gastropoda – Snails, slugs, nudibranchs,
limpets, etc. (90,000+ species)
– Single shelled or no shell
– Means “stomach (or belly) foot”
– Body undergoes torsion - 180º rotation of internal
organs, so that the anus ends up behind the head
and waste products can exit the shell
– Radula for feeding
• Two types: one for scraping found in herbivores and
one that is piercing found in carnivores
– Many have an opercula – trap door that closes off
the shell for protection made of chitin
• Class Bivalvia (Pelecypoda) – clams,
mussels, oysters, scallops, etc.
– Two shells that they can close tightly for
protection
– Filter feeders that brings in water and food
using a siphon
– Some are burrowers, others attach themselves
to rocks (most are sedentary)
– Some can manufacture pearls by secreting
nacre to coat irritating particles
• Class Cephalopoda – squids, octopuses,
cuttlefish, and nautilus
– “head foot” because the feet (tentacles) are
attached to the head
– Shell is either reduced (internal pen) or absent
in all except for the nautilus
– Fast moving predators that use “jet” propulsion
by expelling water through a siphon
– Mouth with a beak for feeding on fish
– Major types:
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Squid: 8 short arms and 2 long feeding tentacles
Octopus: 8 arms
Cuttle fish: 10 arms
Nautilus: only one with external shell