|
Answer» Answer: 3. snail Explanation: Mollusca - This is the second largest animal PHYLUM.
- Mollusca are terrestrial or aquatic (marine or FRESH water) having an organ-system level of organisation.
- They are bilaterally symmetrical, triploblastic and coelomate ANIMALS.
- Body is covered by a calcareous shell and is unsegmented with a distinct head, muscular foot and visceral hump.
- A soft and spongy layer of skin forms a mantle over the visceral hump.
- The space between the hump and the mantle is called the mantle cavity in which feather like gills are present. They have respiratory and excretory functions.
- The anterior head region has sensory tentacles. The mouth contains a file-like rasping organ for feeding, called radula.
- They are usually dioecious and oviparous with indirect development.
- Examples:
- Pila (Apple snail),
- Pinctada (Pearl oyster),
- Sepia (Cuttlefish),
- Loligo (Squid),
- OCTOPUS (DEVIL fish),
- Aplysia (Sea-hare),
- Dentalium (Tusk shell)
- Chaetopleura (Chiton).
|
