Apis (Honey bee), Bombyx (Silkworm), Laccifer (Lac insect) Vectors – Anopheles, Culex and Aedes (Mosquitoes) Gregarious pest – Locusta (Locust) Living fossil – Limulus (King crab). . . Phylum – Mollusca This is the second largest animal phylum (Figure .
). Molluscs 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 . Figure . Examples of Arthropoda : (a) Locust (b) Butterfly (c) Scorpion (d) Prawn (c) (d) Figure . Examples of Mollusca : (a) Pila (b) Octopus 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) and Chaetopleura (Chiton). . . Phylum – Echinodermata These animals have an endoskeleton of calcareous ossicles and, hence, the name Echinodermata (Spiny bodied, Figure .
). All are marine with organ-system level of organisation. The adult echinoderms are radially symmetrical but larvae are bilaterally symmetrical. They are triploblastic and coelomate animals.
Digestive system is complete with mouth on the lower (ventral) side and anus on the upper (dorsal) side. The most distinctive feature of echinoderms is the presence of water vascular system which helps in locomotion, capture and transport of food and respiration. An excretory system is absent. Sexes are separate.
Reproduction is sexual. Fertilisation is usually external. Development is indirect with free-swimming larva. Examples: Asterias (Star fish), Echinus (Sea urchin), Antedon (Sea lily), Cucumaria (Sea cucumber) and Ophiura (Brittle star).
. . Phylum – Hemichordata Hemichordata was earlier considered as a sub-phylum under phylum Chordata. But now it is placed as a separate