Question

classification of mollusca​

Answer 1

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• Classification of mollusca

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Explanation:

Classification of Mollusca

Following are the classification of Mollusca:

Aplacophora or Solenogasters☈

• The body is cylindrical or bilaterally symmetrical.

• These are devoid of the head, shell, mantel, nephridia, and foot.

• The digestive ceca is absent.

• Spicule-bearing cuticle covers the body.

• It contains a dorsal longitudinal keel or crest.

• E.g. Neomenia, Chaetoderma

Monoplacophora☈

• The body is bilaterally symmetrical.

• The head is devoid of eyes and tentacles.

• Respiration occurs through gills which are externally located.

• The nitrogenous waste is excreted out through nephridia.

• E.g. Neopilina

Polyplacophora☈

• Their body is dorsoventrally flattened like a leaf, and are bilaterally symmetrical.

• The shell is composed of 8 longitudinal plates.

• They have a well-developed radula.

• The ventral foot is flat.

• E.g. Chiton, Cryptochiton.

Gastropoda☈

• They are found either on land or in fresh and marine water.

• The head bears tentacles, eyes, and a mouth.

• The shell is spiral in shape.

• The foot is flat and large.

• E.g. Haliotis, Pila

Scaphopoda☈

• Found in the marine environment.

• The eyes and tentacles are absent.

• The foot is reduced.

• The body is bilaterally symmetrical.

Pelecypoda☈

• They reside in aquatic habitats.

• The body is bilaterally symmetrical and compressed laterally.

• The body has no distinct head.

• They usually burrow in mud and sand.

• E.g. Mussels, Unio

Cephalopoda☈

• They are mostly found in the marine environment.

• The shell is either external, internal, or not present at all.

• They have separate sexes.

• The development is direct.

E.g. Octopus, Spirula

⬤Mollusca Examples⬤

Following are a few examples of the animals belonging to phylum Mollusca:

• Pila (Apple snail)

• Limax (Slug)

• Unio (Freshwater mussel)

• Turbinella (Shankha)

• Helix (Garden snail)

• Octopus (Devilfish)

• Loligo (Squid)

✯︎Key Points on Mollusca✯︎

• Phylum Mollusca is the second largest phylum.

• A few molluscs such as Unio possess green glands which mimic the liver in vertebrates.

• They possess osphradia to test the chemical nature of water.

• The statocysts maintain body equilibrium.

• Octopus has 8 arms and contains no shell. They also possess ink glands for protection.

• The blood is blue or green in colour due to the presence of a pigment containing copper called haemocyanin.

• They possess a myogenic heart.

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