Phylum Mollusca general Characters and Classification

Phylum – Mollusca
Ex- Chiton, Dentalium, Pila, Unio, Sepia, Octopus

Chiton
Phylum     Mollusca    Soft bodied animal
Class    Amphineura    Mouth and anus terminal
Order    Chitonina    Valves of shell bear toothed insertion plates
Genus     Chiton    Presence of 8 dorsal shell plates

Characters:

1.     Body soft and unsegmented.

2.     An exoskeleton in the form of shell.

3.     Presence of 8 dorsal shell plates.

4.     Respiratory organ ctenidia.

5.     Presence of creeping foot.

Head is not well differentiated


Dentalium

Phylum     Mollusca        Soft bodied animal
Class        Scaphopoda    Tusk like shell
Genus       Dentalium
Eyes and tentacles absent.

Characters:

1.     Body elongated, bilaterally symmetrical.

2.     A tusk like shell, open at both the ends enclosing the body.

3.     Mouth located on the oral proboscis.

4.     Foot conical narrow and trilobed.

5.     Nervous system with paired ganglia.

Pila
Phylum     Mollusca    Soft bodied animal
Class         Gastropoda    Exhibit torsion
Order        Mesogasropoda    Monopectinate gill
Genus       Pila     Shell is external and round

Characters:

1.     Body consist of head, foot, mantle and visceral mass

2.     Head consist of pair of tentacles, pair of eyes with stalk

3.     Single osphradium is present

4.     Respiratory organ ctenidium and pulmonary sac

5.     Foot is large and ventral

Unio





Sepia:
Phylum     Mollusca    Soft bodied animal
Class    Cephalopoda    Foot is present in head region
Order    Decapoda    Presence of 10 arms
Genus     Sepia
Body consist of head and trunk connected by neck

Characters:

1.     Mantle cavity small and restricted to right side.

2.     Head bears pair of cephalic tentacles and rhinophores

3.     Presence of parapodia

4.     Foot muscular, elongated and pointed posteriorly

5.     A pair of small eyes at the bases of rhinophores

Octopus
Phylum     Mollusca    Soft bodied animal
Class    Cephalopoda    Foot is present in head region
Order    Octopoda    Presence of 08 arms
Genus     Octopus    Body rounded and differentiated into head and visceral hump

Characters:

1.     Head region contains 8 elongated arms with suckers

2.     Eyes 2 and large

3.     Long arms, effective both in swimming and capturing the prey

4.     In male left forth arm is modified into hectocotylised arm for easy transfer of sperms in the body of female.

5.     Siphon highly developed

Mytilus

Phylum     Mollusca    Soft bodied animal
Class    Bivalvia    Shell with two valves
Order    filibranchiata    Gills single paired and large
Genus     Mytilus
Line growth increases in lateral direction

Characters:

1.     Body is laterally compressed.

2.     Shell consist of 2 valves

3.     Shell narrow anteriorly broad posteriorly

4.     Byssus gland and byssus threads are present

Byssus threads are used for attachment with substratum



Pearl Oyster
Phylum     Mollusca    Soft bodied animal
Class    Bivalvia    Shell with two valves
Order    Pseudolamellibranchiata    shell walls may be equal or unequal
Genus     Pinctata
Adductor muscle single and large

Characters:

1.     It is well known for use in production of pearl

2.     Shell surface coarse, irregular

3.     Left shell valve large, right shell valve small

4.     Gills plated with vertical folds.

5.     Large posterior adductor muscle is present.

Aplysia:
Phylum     Mollusca    Soft bodied animal
Class    Gastropoda    Exhibit torsion
Order    Anapsidea    Shell internal
Genus     Aplysia
Body soft, shiny, fleshy

Characters:

1.     Mantle cavity small and restricted to right side.

2.     Head bears pair of cephalic tentacles and rhinophores

3.     Presence of parapodia

4.     Foot muscular, elongated and pointed posteriorly

5.     A pair of small eyes at the bases of rhinophores