MOLLUSCS
(phylum mollusca)
– many of our ideas of sea monsters come from molluscs.
– also provide many types of food – think of all the molluscs that we eat.
| CHARACTERISTICS OF MOLLUSCS
BODY PLAN
1) FOOT
2) VISCERAL MASS
3) MANTLE
mantle cavity
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– most have soft bodies protected by a hard shell
– The coelom is mainly present around the heart – most have a radula = rasping tongue
has 3 distinct parts
– muscular, used for locomotion – in cephalopods modified into tentacles
– contains digestive organs, excretory organs, and the heart
= fleshy outer layer covering visceral mass – has mucous glands and nerve endings – secretes the shell
– lies between the mantle and the visceral mass – contains organs that function in gas exchange between blood and – water (gills) – air (lung)
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CLASSES OF MOLLUSCS
| 1) gastropods (stomach-foots)
= snails, slugs, sea snails, sea slugs
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– most numerous = 5/6 of molluscs
– flat foot – shell is one piece, coiled, or absent – head has tentacles and eyes on stalks – have a radula
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| 2) bivalves (two-shells)
= clams, mussels, and oysters
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– have two shells
– right and left shells hinged dorsally – no head, tentacles or radula – adapted to live in mud – feed by filtering particles from water
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| 3) cephalopods
(head-foots)
= squids, octopus |
– no shells or else a small internal shell
– large head and well-developed eyes – active predators – foot modified into crown of 8 – 10 tentacles with suckers around mouth – foot used in locomotion – expel water from mantle cavity (jet propulsion). – mouth has a horny beak and a radula – some squids are largest invertebrates – squirt inky substance in defense
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| 4) chitons
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– have a radula (rasping tongue)
– eight articulating plates, or valves
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| 5) nautilus | – “living fossils,” thought extinct for millions of years, found again in 1952
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