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Adaptive Radiation of Molluscs

The document describes the key characteristics of mollusc classes including their shell, head, mantle, gills, foot, radula, and larval forms. It finds that classes like Monoplacophora have a single dorsal shell while Bivalvia have two hinged valves. Gastropoda mostly have a single coiled shell and a well-developed head and foot, using their radula as a grater. In contrast, Cephalopoda have a reduced or absent shell and use tentacles and a beak instead of a radula to feed.

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655 views2 pages

Adaptive Radiation of Molluscs

The document describes the key characteristics of mollusc classes including their shell, head, mantle, gills, foot, radula, and larval forms. It finds that classes like Monoplacophora have a single dorsal shell while Bivalvia have two hinged valves. Gastropoda mostly have a single coiled shell and a well-developed head and foot, using their radula as a grater. In contrast, Cephalopoda have a reduced or absent shell and use tentacles and a beak instead of a radula to feed.

Uploaded by

ali zahoor
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Adaptive Radiation in Molluscs

Class: Monoplacophora
shell: forms a single dorsal conical shell
head: reduced
mantle: covers undersurface of shell
gills: 5 or 6 pairs
foot: broad flat ventral, for creeping
radula: present
larva:

Classes: Caudofoveata & Solanogastres (formerly Cl. Aplacophora)


shell: none, but with calcareous scales and spicules in mantle
head: reduced
mantle: encloses animal
gills: absent, or present in cloaca
foot: reduced to small ridge within ventral groove
radula: present in some, for piercing
larva: trochophore

Class: Polyplacophora (Chitons)


shell: modified into eight overlappingdorsal plates
head: present
mantle: greatly enlarged, modified into "girdle" around base of shells
gills: present
foot: broad flat ventral, for gliding movement
radula: present
larva: trochophore

Class: Scaphapoda (Tusk Shells or Tooth Shells)


shell: anteroposteriorly elongated into tapering
tusk-like tube open at both ends
head: reduced to short proboscis
mantle: lines inside of shell, used for respiration instead of gills
gills: none; oxygen diffuses across mantle
foot: conical, elongated ventrally and used for burrowing
radula: present
larva: trochophore & veliger
Class: Bivalvia (Clams)
shell: two lateral, usually symmetrical, hinged valves
head: absent
mantle: lines inside of both shells; forms siphons for water flow
gills: most with pair of large gills; also used for feeding and as
marsupium
foot: ventral, wedge-shaped, very muscular, used for burrowing
radula: absent
larva: marine forms with trochophore & veliger; fw - glochidia

Class: Gastropoda (Snails)


shell: most with single shell often coiled spirally
head: present and well developed
mantle: lines inside of shell; in pulmonates forms lunglike sac
gills: some with single gill; terrestrial forms without
foot: ventral, very large, used for gliding movement
radula: highly developed as grater, rasp, brush or comb
larva: marine forms with trochophore & veliger

Class: Cephalopoda
shell: most reduced to internal pen or absent
mantle: forms external protective covering over visceral mass
gills: 2 to 4 present within mantle cavity
foot: modified to form siphon and tentacles
radula: present, takes in food cut with beak
larva: none

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