Mollusc

s

By: Sameena Khokhar

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 1.Chitons2.Bivalves 3.Scaphopods4.Cephalopods5.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.” 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.