Mollusca

                                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

 

Neomania sp (Aplacophora)

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

 

Dantalium 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

                                                  

                 

 This is just a brief overview on Phylum Mollusca...................

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