Molluscs By: Sameena Khokhar

The term mollusc means “soft The term mollusc means “soft.” A mollusc is a diverse animal and is a member of the phylum Mollusca group. Around eighty five thousand species of molluscs have been recognized. Molluscs reproduce sexually. Slugs and snails mate to fertilize eggs. Aquatic molluscs lay eggs that hatch into small free-swimming larvae. Many molluscs have hard external shells which they use for protection. Molluscs range in size and are usually found in marine habitats, but a few molluscs like snails and slugs live on land where there is high moisture.

types of Molluscs Chitons Bivalves Scaphopods Cephalopods Gastropods

chitons

Chitons also known as “sea cradles” are characterized by a dorsal shell composed of eight separate shell plates bound together by a leathery girdle that provides good protection from impacts above. They like cool, temperate, and tropical waters. Chitons  are primary consumers or herbivores that eat algae, bryozoans, diatoms, and sometimes bacteria. They reproduce by releasing eggs and sperm into the ocean. Chitons live in high intertidal zones, in tidal pools or between rocks.

Bivalves

Bivalves have a shell composed of two hinged valves formed of calcium carbonate that is secreted from their mantle. Bivalves feed on plant detritus, bacteria, and algae. They reproduce by creating eggs and most of the bivalve larvae that hatches feed on diatoms. The bivalve class includes scallops, clams and mussels. They live in the littoral or intertidal zone of the ocean. There are four different life strategies that bivalves exhibit: epifaunal, infaunal, boring and free-moving. Epifaunal bivalves attach themselves to hard surfaces. Infaunal bivalves bury themselves. Bore bivalves go onto solid surfaces such as wood or rock. Free-moving bivalves use their muscular foot to dig into sand and soft sediments.

Scaphopods

Scaphopods also known as “boat footed” are molluscs whose shells are shaped like the tusks of animals. They feed on microscopic organisms or zooplankton. Scaphopods reproduce sexually by external fertilization through eggs that eventually hatch into free-swimming larva. They live on soft substrates offshore or in seafloor sediments. In total, there are about four hundred species of scaphopods. They share some similar features with bivalves, but are so different than other molluscs to be placed in the same class.

cephalopods

Cephalopods also known as the “ink fish” are characterized by a two-sided body symmetry, a bulging head, and a set of arms or tentacles. These carnivores eat fish, worms, crustaceans, and other mollusks. Most cephalopods use a semelparous reproduction strategy: where they lay small eggs in a batch and die afterwards. The cephalopod class includes squids, octopods, cuttlefish and nautiloids. They are found in marine oceans, but most of them can handle freshwater. Cephalopods occupy the ecological niche of Epipelagic Fish in the Antarctic Polar Frontal Zone.

Gastropods

Gastropods means “stomach-foot Gastropods means “stomach-foot.” They are characterized by torsion which is a process that results in the rotation of the visceral mass and mantle on the foot. Most gastropods are herbivores, using their radula to scrape algae and diatoms off the surface of rocks. Some of them eat lettuce. Gastropods reproduce asexually and sexually. Pulmonate snails are capable of self-fertilization. The gastropod class includes snails, limpets, abalones and nudibranchs. They occupy every marine niche ranging from the deepest ocean basins to the supralittoral, as well as freshwater habitats, and other inland aquatic habitats like salt lakes.

Works Cited Karleskint, George, Jr., Richard Turner, and James W. Small, Jr. INTRODUCTION to Marine Biology. Third ed. N.p.: n.p., n.d. Print.