Tuesday, May 16, 2006


The phylum mollusca are known to be the largest of all phyla and provide some of the most familiar animals such as clams, mussels, squids and octopus. They are well known for their decorative shells or as sea food. The phylum Mollusca also includes lesser known forms such as the chitons, tusk shells, and solenogasters, among others.

The live in almost all parts of the world, from the deep water bodies like oceans to high up on mountains. The molluscs need moisture in order for them to stay alive; they must keep their soft bodies moist all the times. those which live in hot dry deserts environments, this is done by curling up in their shell, secreting a mucous plug and staying holed up until the next bit of moisture comes along.

The phylum Mollusca uses the chemicals and nutrients to build themselves protective shelters or shells. They have different shell structures however there are quite a few groups that have either reduced or internal shells, or no shell at all.

For example, the alplacophora are wormlike, bilaterally symmetrical animals living at moderate, to very great depths, usually on or in soft bottoms. They have no shell, but have calcareous spicules in the body surface. The bivalva or Apelecypoda does not have the shells because they live in water with ph greater than 5.

The polyplacophora have the shell consisting of eight, usually overlapping plates held together by a leathery strap. The polyplacophora or chitons are marine inhabitants and most make a living by grazing algae from rocks and other hard substrates. The most distinctive characteristic of chitons is their eight-piece shell.

The scaphopodia commonly known as tusk shells, they are bilaterally symmetrical and their elongate, tubular, tapering shells are open at both ends. The shell is usually an elongated, cylindrical tube; open at both ends, and slightly curved. However, some of the scaphoda shells are shaped more like a distended cucumber. The shell is usually heavily uneven and has small slits at the narrowest end.

The cephalopoda class includes octopus, squid, cuttlefish and nautilus. Tentacles surround the head, and a funnel coming from the mantle produces jet propulsion.
Externally, the shell of the nautilus is creamy white with broad reddish-brown stripes. Inside it is brilliant, iridescent mother-of-pearl.

The Gastropods generally have a single-valved shell, which is usually spiralled; this brings their organs from a posterior position to an anterior position behind their head. In most cases, the soft animal is able to retract into their shells for protection.

The Monoplacophorans possess a single, large, bilateral shell. The shell is a simple depressed limpet or disk -shaped valve, less than 25 millimetres across usually and is often thin and fragile.

The shell serves both protective and supportive purposes. The one feature common to all molluscs is the presence of a fleshy mantle. This is a fold or lobe of fleshy material, which secretes, modifies and lines the shell.


1. Wikipedia contributors. Caudoveata [Internet]. Wikipedia, The Free Encyclopedia; 2006 April 9, 09:01 [cited 2006 May 4]. Available from:

2. Wikipedia contributors. Aplacopra [Internet]. Wikipedia, The Free Encyclopedia; 2006 April 20, 20:04 [cited 2006 May 4]. Available from:

3. Wikipedia contributors. Polyplacophora [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 04, 15:32 [cited 2006 May 4]. Available from:

4. Wikipedia contributors. Monoplacophora [Internet]. Wikipedia, The Free Encyclopedia; 2006 April 22, 20:03 [cited 2006 May 4]. Available from:

5. Wikipedia contributors. Bivalvia [Internet]. Wikipedia, The Free Encyclopedia; 2006 April 23, 12:22 [cited 2006 May 4]. Available from:

6. Wikipedia contributors. Scaphopoda [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 04, 20:07 [cited 2006 May 4]. Available from:

7. Wikipedia contributors. Gastropoda [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 04, 20:07 [cited 2006 May 4]. Available from:

8. Wikipedia contributors. Cephalopod [Internet]. Wikipedia, The Free Encyclopedia; 2006 May 3, 04:57 [cited 2006 May 4]. Available from:

Mr Lufuno Mukwevho
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