Classification of Mollusca
Class: Monoplacophora
The term "Monoplacophora" comes from the Greek words mono (one), plax (plate), and pherein (bearing), meaning "bearing one plate."
1) The shell consists of a single piece or valve.
2) These animals are marine.
3) Their body is segmented and bilaterally symmetrical.
4) The head lacks eyes and tentacles.
5) The foot is flat and located on the ventral side.
6) The mantle forms a circular fold around the body.
Example: Neopilina, a species considered a link between Annelida and Mollusca.
Class: Polyplacophora
1) Primarily marine organisms.
2) The shell is composed of eight distinct plates.
3) The body is elliptical, dorsally convex, and ventrally flattened.
4) The head is present but lacks eyes and tentacles.
5) The foot is flat and located on the ventral side.
6) Development includes an indirect larval stage with a trochophore.
7) The mantle is present.
Example: Chiton.
Class: Scaphopoda
1) These are marine species.
2) The body is elongated and enclosed in a tusk-shaped shell.
3) The shell is cylindrical, with a mouth located on the head.
4) The foot is conical and adapted for digging.
5) Development involves a trochophore larva.
6) The mantle is single-lobed and tubular.
Example: Dentalium.
Class: Gastropoda
1) Found in both aquatic and terrestrial habitats.
2) The body is unsegmented and asymmetrical.
3) The head is distinct and equipped with tentacles, eyes, and a mouth.
4) The foot is broad, flat, and muscular, functioning as a sole for locomotion.
5) The shell is univalve, giving rise to the alternative name "Univalvia."
6) Development includes a trochophore or veliger larva.
7) The mantle assists in respiration.
Examples: Helix (Snail), Limax (Slug), Pila (Apple Snail).
1) Mostly marine organisms.
2) The body is bilaterally symmetrical, divided into a head and trunk.
3) The head features large eyes, similar to those of vertebrates, and a mouth.
4) The foot is located on the head and has evolved into arms and a siphon.
5) The shell may be absent or internal.
6) They possess a closed circulatory system.
7) The mantle may or may not be present.
8) Development is direct.
Examples: Sepia, Octopus, Loligo (Squid).
Class: Bivalvia
1) The body is laterally compressed.
2) The shell consists of two valves, leading to the name "Bivalvia."
3) The head is not distinct.
4) The foot is tongue-shaped.
5) The mantle is paired, consisting of right and left lobes.
6) Development involves an indirect larval stage, often with a glochidium stage.
7) Many bivalves are known for forming pearls, secreted by the shell gland in the mantle.
Examples: Unio, Oyster.
