Mollusca (Moderate)

Scientific study of mollusks is called malacology.

This is the correct order. The numbers of species in the four phyla are as follows:
Arachnids - 1,02,248
Mollusks - 85,000
Crustaceans - 47,000
Corals - 2000

Aplacophores possess aragonite spicules on their epidermis. These animals lack calcareous shells.

The thread-like cilia bearing tentacles of Scaphopoda are called captacula. These are used to catch and manipulate prey.

Phylum molluska has the second largest number of species.

Statocysts are situated in the foot of mollusks. These are balance receptors which maintain balance during movement of mollusks.

Class aplacophora includes worm-like animals with no shell and a rudimentary body structure.

Helcionelloida are fossils; snail-like mollusks such as latouchella.

2 classes have both marine and freshwater habitats. Only bivalves and gastropods are found in both freshwater and seawater.

Deroceras is a serious pest in greenhouses, grove snail is noxious to crops and limax is a pest slug.

Bivalves are excellent water quality biosentinels. Therefore, they were exploited in Mussel Watch Program to measure the level of contamination of water.

Pinctada margaritifera and Pinctada martensii (marine oysters) are known for their best natural pearls. They live in the tropical and subtropical waters of the Pacific Ocean.

The veliger is the second larval stage in the development of gastropods. Veliger is exclusively aquatic and typically feeds on phytoplankton.

Schistosomiasis is a disease caused by the fluke worm, Schistosoma. The parasite itself is not a mollusk, but all the species have freshwater snails as intermediate hosts.

Sea silk is produced by a large marine bivalve mollusk, Pinna nobilis.