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Molluscs Notes

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

 

 

 

 

 

– 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)

 

 

 

CLASSES OF MOLLUSCS

 

1) gastropods (stomach-foots)

 

= snails, slugs, sea snails, sea slugs

 

– 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

 

 

2) bivalves (two-shells)

 

= clams, mussels, and oysters

 

– 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

 

 

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

 

 

4) chitons

 

– have a radula (rasping tongue)

– eight articulating plates, or valves

 

 

5) nautilus – “living fossils,” thought extinct for millions of years, found again in 1952

 

 

posted by Marc Bernard Carmichael in Biology Eleven,Biology Eleven Notes and have No Comments

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