Mollusca

Mollusca:

  • Molluscs are the second largest animal phylum.
  • Molluscs can be terrestrial or aquatic
  • They have respiratory and excretory functions.

 

Characteristics-

  • Body Organisation:
    • Molluscs are triploblastic organisms with bilateral symmetry.
    • Molluscs exhibit organ- system level of organisation and are coelomate animals.
    • They have a soft body covered by a mantle, which may secrete a protective shell made of calcium carbonate in many species.
    • Molluscs typically exhibit three main body parts: the head, visceral mass (containing organs), and foot (used for locomotion).
    • The anterior head region has sensory tentacles.
  • Locomotion:
    • Molluscs employ various modes of locomotion.
    • Many molluscs use a muscular foot for crawling, burrowing, or attachment to surfaces.
    • Some molluscs, like snails, move by rippling waves of muscle contractions called "foot crawling."
    • Certain molluscs, such as squid and octopuses, are highly adapted swimmers using jet propulsion.
  • Reproduction:
    • Molluscs can reproduce both sexually and asexually.
    • Sexual reproduction involves separate sexes (male and female).
    • Fertilisation is usually internal, with the transfer of sperm from males to females.
    • Some molluscs exhibit direct development, with offspring resembling miniature adults.
    • Others undergo indirect development, with larval stages before reaching the adult form.
  • Feeding Strategies:
    • Molluscs exhibit diverse feeding strategies depending on their ecological niche and feeding apparatus.
    • Most molluscs are herbivores or filter feeders, consuming algae, plant matter, or suspended particles.
    • Some molluscs are carnivores, preying on other organisms.
    • Molluscs possess specialised feeding structures, such as radula (a toothed ribbon) in snails and beak-like jaws in cephalopods.
  • Examples:

Pila (Apple snail), Pinctada (Pearl oyster), Sepia (Cuttlefish), Loligo (Squid), Octopus (Devil fish), Aplysia (Sea-hare), Dentalium (Tusk shell) and Chaetopleura (Chiton).