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Transcript of BIOLOGY
Gastropods (Class Gastropoda) include snails and slugs. Gastropods live in marine, freshwater, and terrestrial habitats. Gastropods is the most diverse class of mollusc with more than 60,000 species.
Cephalopods (Class Cephalopoda) include octopus, squid, cuttlefish and nautilus. Cephalopods exhibit bilateral symmetry and in most members of the group the shell has either been internalized or lost. The exception is the nautilus which has retained a shell.
Bivalves (Class Bivalvia) are marine and freshwater molluscs that have a shell that consists of two valves that are hinged at the back. Bivalves have no head, their body consists of a wedge-shaped foot.
Other classes not in syllabus
Many gastropods have one shell in which the animal can withdraw. The shell is usually coiled, and may be 'left-handed' or sinistral (spiraled counter-clockwise) or 'right-handed' or dextral (clockwise). Gastropods move using a muscular foot.
All young (larval stage) gastropods undergo a process called torsion, in which the entire top of their body twists 180 degrees on their foot. This results in the placement of the gills and anus above the head. Gastropods have adapted in a variety of ways to avoid polluting their breathing water with their own wastes.
Due to torsion, adult gastropods are asymmetrical in form.
Such a diverse group of organisms has diverse feeding mechanisms. Some are herbivores, some carnivores. Most feed using a radula. The whelk, a type of gastropod, use their radula to drill a hole into the shell of other organisms for food.
Food is digested in the stomach. Because of the torsion process described earlier, the food enters the stomach through the posterior (back) end, and wastes leave through the anterior (front) end.
Some gastropods have both sexes; some are hermaphroditic. One interesting animal is the slipper shell, which may start out as a male and then change to a female.
Depending on the species, gastropods may reproduce by releasing gametes into the water, or by transferring the male's sperm into the female, who uses it to fertilize her eggs.
Shell divided by septa, with chambers connected by the sipnucle; a vascularised strand of tissues contained within a tube of calcium carbonate
Closed circulatory system
Foot modified to form flexible arms and siphon
Ganglia used to form a large brain enclosed in a cartilagenous cranium
Cephalopods are carnivorous. The diet varies depending on the species, but can include other mollusks, fish, crustaceans and worms. Cephalopods can grasp and hold their prey with their arms and then break it into bite-sized pieces using their beaks.
Unlike some other marine invertebrates, there are both males and females in cephalopod species. Cephalopods usually have a courting ritual when they mate and may change into brilliant colors. The male transfers a sperm packet (spermatophore) to the female, the female lays eggs, and the eggs hatch as juveniles.
body flattened laterally
includes clamps, scallops, muscle and oyster
2 major subclasses
Actually phlum mollusa have
; Class Aplacophora, Class Bivalvia, Class Caudofoveata, Class Cephalopoda, Class Gastropoda, Class Monoplacophora, Class Polyplacophora and Class Scaphopoda.
body of mollusca consists of two parts; a head-footand a visceral mass
. In general, the head-foot of a mollusc is an elongated, soft structure that encompasses an anterior head and an elongated foot
Mollusca are more closely related to annelids than they are to arthropods.
approximately 100,000 species of mollusks
. Of all the molluscan subgroups, the
most divers group is the gastropods.
Some mollusca don’t have a shell.
Some mollusca don,t have a head.
The giant squid and the giant clam
are among the
world’s largest mollusca.
Second largest phlum
in the animal kingdom after Phlum Arthropoda.
Bivalves have a double shell
, articulated through the ligaments are very strong and flexible, which can be relaxed to
allow the opening of the shell
facilitating entry and exit of water
. When the shell is attacked, the skin maintains tight muscles. Bivalves feed on organic material and detritus floating, sucked through a siphon frayed at the edges of the shell. Water is released through the siphon is smaller.
Pearls and mother of pearl shells produced by mollusks.
Pearl occurs when a foreign object, like a grain of sand or parasite remains between the two shells of a. The object wrapped by the calcium carbonate until it will be isolated from the body shell. By artificially introducing a small piece of material into the body shell, a small pearl is made in the command
BENEFITS TO HUMAN
1)Serves as food
in Europe, South Africa, West Indies, Carlifonia and Japan
2)Used as fish bait
Serves as food in cuisine
Squid is a good source for zinc and manganese and high in copper selenium, vitamin b12 and riboflarin
Teh internal shell of cuttlefish is sold in pet trade as calcium source for birds
source of food for humans
used in controlling pollution
they can be compresed into concrete or plasters to make decoratives
can be used to embellish picture frames, mirrors or other craft items
as body decorations, utensils, scrapers and cutting implements
3M1S23 KMPH 2013/14
MUHAMMAD AKMAL BIN SUHAIMI
NORLILY BT ZULKIFLI