What is the difference between mollusks and mollusc

Chitons live worldwide, in cold water, warm water, and the tropics. Most chiton species inhabit intertidal or subtidal zones, and do not extend beyond the photic zone. Some species live quite high in the intertidal zone and are exposed to the air and light for long periods. Bivalvia is a class of marine and freshwater molluscs with laterally compressed bodies enclosed by a shell in two hinged parts.

Bivalves include clams, oysters, mussels, scallops, and numerous other families of shells. The majority are filter feeders and have no head or radula. The gills have evolved into ctenidia, specialised organs for feeding and breathing. Most bivalves bury themselves in sediment on the seabed, while others lie on the sea floor or attach themselves to rocks or other hard surfaces.

The shell of a bivalve is composed of calcium carbonate, and consists of two, usually similar, parts called valves. Gastropoda includes shell-bearing species as well as species with a reduced shell. These animals are asymmetrical and usually present a coiled shell.

Shells may be planospiral like a garden hose wound up , commonly seen in garden snails, or conispiral like a spiral staircase , commonly seen in marine conches. The visceral mass in the shelled species displays torsion around the perpendicular axis on the center of the foot, which is the key characteristic of this group, along with a foot that is modified for crawling. Most gastropods bear a head with tentacles, eyes, and a style.

A complex radula is used by the digestive system and aids in the ingestion of food. Eyes may be absent in some gastropods species.

The mantle cavity encloses the ctenidia singluar: ctenidium as well as a pair of nephridia singular: nephridium. Cephalopods are a class of shell-bearing animals as well as mollusks with a reduced shell.

They display vivid coloration, typically seen in squids and octopi, which is used for camouflage. All animals in this class are carnivorous predators and have beak-like jaws at the anterior end. Most mollusk species only live in the ocean, but some live in freshwater or on land. In Michigan there are about species of mollusks known, with more to be found. There are three main groups of mollusks. Snails Gastropoda are the most diverse group, there are tens of thousands of species.

Nearly all snails grow a spiral shell that is all one piece. A few snail groups have stopped growing shells; they're called slugs. The next largest group is Bivalvia , the clams, oysters, and mussels. These are mollusks with two shells that they can close up tight for protection. Taxon crustacea come under phylum arthropods and comprise of 35, species. The unique features of arthropods are the presence of jointed appendages, tough chitinous exoskeleton, compound eyes, and endocrine system.

Thus, the whole body of crustaceans has two prominent parts; abdomen and cephalothorax Cephalon and thorax fused to form a cephalothorax. Shield-like carapace closes the cephalothorax.

Moreover, these creatures have three pairs of appendages as mouth parts, two pairs of antennae, and several pairs of legs. Also, their number of leg pairs varies among the species.

The unique feature of crustaceans is the presence of two pairs of antennae that that is not present in other arthropods. Furthermore, all the segmented appendages except the first pair of antennae of crustaceans are biramous and present in all the body segments. Generally, all crustaceans are largely aquatic and can be found in both marine and freshwater habitats. Marine crustaceans are crabs, shrimps, lobsters and barnacles while freshwater crustaceans include some crayfish, crabs and copepods.

Few species are terrestrial e. Also, planktonic crustaceans like krill and larval crustaceans act as the primary food source in marine ecosystems. Some crustaceans like lobsters and crayfish are important as a food source for humans.

In larger crustaceans, feathery gills act as respiratory organs, whereas in smaller crustaceans, gas exchange takes place through their cuticle. Phylum Mollusca is the second largest and extremely diverse group with more than , identified species in kingdom Animalia.

Molluscs live in various types of environments including both aquatic and terrestrial ecosystems. Further, this group includes snails, slugs, scallops, clams, octopuses, cuttlefish, oysters, etc. The body size of molluscs varies from microscopic to huge. For example, the largest molluscs are the giant squid with the body size of 15 m long and weigh up to about kg.

Molluscs have soft unsegmented bodies. The characteristic feature of all molluscs is the presence of mantle; a thick epidermis, which covers the dorsal side of the body. Some molluscs have outer calcareous shells, which is secreted by the mantle.

All the molluscs except cephalopods have a muscular foot as the organ of locomotion.