PHYLUM MOLLUSCAColwyn Sleep

GENERAL CHARACTERISTICS

-Molluscs are free living forms and can aquatic, terrestrial, or amphibious.-Mollusk bodies are soft and unsegmented, enclosed in a mantle, and usually covered by a shell.

-Mollusc digestive system is complete.-Respiratory organs are in the form of gills called ctenidia.-Locomotive structure is represented by muscular foot.

-Body is differentiated into three regions: head, visceral hump and foot.-Mantle secretes the calcarious shell, which may be external or internal.

-There are four main classes of mollusks: Amphineura (polyplacophora), Bivalvia, Gastropoda, and Cephalopoda.

A FEW OF THE MOLLUSCA CLASSES…

Bivalves Bivalves are mollusks belonging to

the class Bivalvia. They also are called pelecypods. They typically have 2- part shells with both halves being symmetrical . The class has 3,000 species including scallops, clams,

oysters, and mussels. They include both marine and fresh water forms. They feed by siphoning and filtering large particles from the water. Some bivalves such as scallops can swim.

Gastropods Gastropods, typified by the snail,

include many different types of species. They live everywhere from gardens, to forests, to deserts and mudflats. The

class gastropods includes limpets, periwinkles, snails, slugs, and sea slugs. Gastropods are mostly are found in

saltwater, but can be found in freshwater as well. Others live near

moist areas, such as swamps or gardens. Some gastropods such as slugs

don’t have shell.

Cephalopods Cephalopods can be found

anywhere in the ocean at any and every depth . They are widely

regarded as the most intelligent of the invertebrates and have well developed skills and brains. All

cephalopods are carnivores. They also have a highly developed eyesight. Some examples of

cephalopods are: octopus, cuttlefish, nautilus, and squid.

SHAPE CHARACTERISTICS

Despite their diversity, all molluscs share characteristics that define their body plan. The body has a head, a foot and a visceral mass. This is all covered with a mantle that typically secretes the shell.

Typically, at least in the more primitive members of each group, there are one or more pairs of gills (called ctenidia) which lie in a posterior cavity or in a posterolateral groove surrounding the foot. The

pallial cavity is the space into which the kidneys, gonads, and anus open.Molluscs are coelomate, although the coelom is reduced and represented by the kidneys, gonads, and

pericardium, the main body cavity which surrounds the heart.They are also Protostomes so the mouth develops first in the embryo.

NERVOUS SYSTEM

The molluscan nervous system nervous system has a dorsal brain, nerve ring, and a pair of solid ventral nerve cords with statocysts (balance organs) and eyes that detect shadows and movement as

major sense organs.

MOVEMENT

Mollusks move with their feet. The feet of different kinds of mollusks are for crawling, digging, swimming, and catching prey. Mollusks have two methods of movement. The first is jet propulsion in which they siphon water through a hole and shoot it out. Clams and bottom

dweller mollusks have feet that they move to get around. They also use them to escape an enemy.

RESPIRATION METHOD AND STRUCTURES

Mollusk reproduction can be simple or very complex. An example of one method is that of the freshwater mollusks. The male releases his sperm, which goes into the ocean, until a female mollusks

catches it and the sperm begins to fertilize. Once fertilized, the egg becomes a swimming form known as a trochophore larva, then develops into a veliger larva. The process then differs as the larva forms

into one of the many different classes of mollusk. Some mollusks, like snails, can become hermaphrodites, meaning they can be a female or a male. They do this to allow for more potential

mates. Other mollusks, such as the oyster can switch between sexes.

EXCRETION METHOD AND STRUCTURES

Many mollusks, including snails have an excretory organ called the nephidrium. This organ is used to maintain fluid balance within snails. Water, minerals, and other substances pass

through the nephidrium. Another vital part of the snail's excretory anatomy is the haemolymph, or heart sac. This organ removes nitrogenous waste from the body of the

gastropod and takes any toxins, minerals and, excesses to remove it from the body.

FEEDING METHOD AND STRUCTURES

To obtain their food, mollusks use their radula, a tongue-like organ that protrudes from the mouth, and scratch a belt of teeth back and forth to loosen and snatch up their food. The amount of teeth a

mollusk has differs from mollusk to mollusk. Some have a single tooth, and others posses hundreds of thousands. An adaptation certain mollusks have is that there is poison contained in their hollow teeth. Some mollusks, the bivalves, are filter feeders. Water rushes in between their two shells and food is

filtered out as it is released.

SURPRISING FACTS

-Mollusks have glands that make mucus, which mollusks use in many important uses such as locomotion, food entrapment and prevention of water loss.

-Some mollusks, like the nudibranch have their lungs out side their body for protection. For example, the nudibranch uses it lungs to sting its predators and get away.

-Molluscs provide us with food, jewelry, tools, and even pets. -Some mollusca are also used for measuring pollution.

-Leeches are a mollusk with a number of medical purposes.

BIBLIOGRAPHYhttp://www.oceanicresearch.org/education/wonders/mollusk.html

http://www.mesa.edu.au/friends/seashores/molluscs.htmlhttp://www.bartleby.com/65/mo/Mollusca.html

http://library.thinkquest.org/26153/marine/mollusca.htm?tqskip1=1http://animaldiversity.ummz.umich.edu/site/accounts/information/Cephalopoda.htmlhttp://animaldiversity.ummz.umich.edu/site/accounts/information/Gastropoda.html

http://animaldiversity.ummz.umich.edu/site/accounts/information/Bivalvia.htmlhttp://encarta.msn.com/encnet/refpages/refarticle.aspx?refid=761572661

http://www.encyclopedia.com/doc/1E1-Mollusca.htmlhttp://www.marietta.edu/~biol/mussels/reprod.html

http://www.bio.umass.edu/biology/conn.river/repro.htmlhttp://www.bio.psu.edu/people/faculty/Hass/hsi98/animals1/mollusks.html

http://en.wikipedia.org/wiki/Molluskshttp://hometown.aol.com/ksmith9526/MolluskInformation.htm

http://www.seasky.org/reeflife/sea2f.htmlhttp://www.oceaninn.com/guides/mollusks.htm