BIOL10005 Lecture Notes - Lecture 19: Monoplacophora, Chiton, Tusk Shell
LECTURE 19
ANIMAL DIVERSITY - FROM MOLLUSCS TO CHORDATES
CHAPTER 39 - ANNELIDS, MOLLUSCS, NEMATODES &
ARTHROPODS
PHYLUM: MOLLUSCA
•Molluscs constitute the second largest animal phylum after the arthropods, with more than
100,000 living species.
•Eg. snails, clams.
•They can be both aquatic and terrestrial animals, most are marine.
•The main groups are:
•Chitons (class Polyplacophora)
•Monoplacophorans (class Monoplacophora)
•Bivalves (class Bivalve; mussels, oysters and cockles)
•Tusk shells (class Scaphopoda)
•Gastropods (class Gastropoda; snails and nudibranchs)
•Cephalopods (class Cephalopoda, squid and octopuses)
MOLLUSCAN BODY PLAN
•Morphologically very diverse in appearance.
•Generalised molluscs (which do not exist exactly as described) are
bilaterally symmetrical, triploblastic, unsegmented coelomate
protostomes.
•There are up to 8 classes of mollusc.
•Visceral mass containing body organs. Covering the visceral mass
is a dorsal body wall called the mantle, which can (and often does)
form shell. The mantle cavity is the space between mantle and main
body where gills (or lungs in terrestrial snails) are found.
•They also have a muscular foot, which is used for
moving, feeding and manipulation.
•Have a broad, tongue like structure called the radula, as
part of their head with specialised mouthparts.
CLASS POLYPLACOPHORA (CHITONS)
•Polyplacophorans (chitons) are exclusively marine,
bilaterally symmetrical molluscs.
•Their shell consists of 8 large plates surrounded by a
girdle of smaller spicules.
•They mostly feed on algae or encrusting organisms, but
some are predators.
•They reproduce sexually, and some brood their young in
their mantle.
CLASS MONOPLACOPHORA
•Monoplacophorans are limpet-like molluscs.
•15 living species discovered so far.
•Typically live very deep in the oceans.
Lecture 19 - Monday 5 September 2016
BIOL10005 - GENETICS & THE EVOLUTION OF LIFE
Document Summary
Phylum: mollusca: molluscs constitute the second largest animal phylum after the arthropods, with more than. Molluscan body plan: morphologically very diverse in appearance, generalised molluscs (which do not exist exactly as described) are bilaterally symmetrical, triploblastic, unsegmented coelomate protostomes, there are up to 8 classes of mollusc, visceral mass containing body organs. Covering the visceral mass is a dorsal body wall called the mantle, which can (and often does) form shell. Class monoplacophora: monoplacophorans are limpet-like molluscs, 15 living species discovered so far, typically live very deep in the oceans. Class bivalvia & filter feeding: bivalves ave two shell plates either side of the body that enclose it, eg. Clams, mussels, oysters: they can be marine and freshwater. They are characterised by two shells and have no distinct head. They have also lost the radula and consequently filter feed via cilia on the surface of their gills (sometimes through their foot): they often live buried in sand.
