PHYLUM MOLLUSCS
Diagnostic Features:
01)Bilaterally Symmetrical Body. Mainly Aquatic
but some are terrestrial.
02)Open circulatory system, enclosed partly by
pericardium. In Cephalopods closed circulatory system present.
03)Sexes Separate. Development via trocophore
& veliger larval stage.
04)Radula Assists in Feeding.
Classification: (Ruppert & Barnes 6th edition 1994 )
Class
Aplacophora
01)
Worm like body.
Shell absent.
02)
Respiration by
Ctenidia(comb like gills)
03)
Head not
distinct, absence of Eyes and sensory tentacle .
04)
Thick mantle,
with calcareous spicules.
Eg- Chaetoderma sp, Neomenia sp, Proneomenia sp
Class
Polyplacophora
01)
Dorso-ventarlly
flattened body.
02)
Radula large and
bears teeth.
03)
Head not distinct
lacks eyes and sensory tentacle.
04)
Between Foot and
mantle cavity, in the pallial groove pairs of gills are present.
Eg- Chiton sp, Chaetopleura sp, Lepidopleura sp
Class
Monoplacophora
01)
Bilaterally
flattened body, with shield like shell.
02)
On the side of
the foot 5-6 pairs of mono pectinate ctenidia are present.
03)
Excretory organs
are Nephridia or renal organ.
04)
Head distinct but
lacks eyes and tentacle
Eg- Monoplacophorus sp, Neopilina sp
Class
Gastropoda
01)
Body Asymmetrical
due to torsion.
02)
Osphradium
present which tests the incoming water & food materials, acts as a chemo
receptor.
03)
Buccal mass with
scrapping radula.
04)
Mantle cavities
possess bipectinale ctenidia.
Eg- Pila sp, Helix sp
Pila sp |
Class
Bivalvia
01)
Laterally
flattened body, body enclosed in 2 lobed mantle.
02)
Radula absent,
Instead mouth possess a pair of labial palps.
03)
Sexes separated,
Development via trocophore & veliger larva.
04)
Head indistinct,
without eyes or tentacle.
Eg- Mytilus sp, Pinctada sp
Class
Scaphopoda
01)
Conical burrowing
foot.
02)
Elongated body
enclosed by mantle.
03)
Gills absent,
instead a part of the mantle serves for gaseous exchange.
04)
A small proboscis
like head, eyes and tentacle absent.
Eg- Dentalium sp, Cadulus sp
Class
Cephalopoda
01)
Shell absent or
reduced.
02)
Foot modified
into prehensile arms, tentacle or siphon.
03)
Head well
developed, with large eyes.
04)
Highly developed
nervous system and sensory organs.
05)
Mouth with jaws
and radula.
Eg- Loligo sp, Octopus sp
Octopus sp |
Reference- Ruppert and Barnes 6th Edition 1994