Clam Dissection
Background Information
Clams are bivalve mollusks. The term bivalve applies to these creatures because they possess two shells which are held together by a hinge in the middle. Clams are unique in that they possess two adductor muscles on opposite ends of the organism along with a hard structured foot that helps it move. The insides fo the shells are usually pearly, and small pieces of sand that may enter the clam may slowly take on a pearly surface. There are approximately 15,000 different species of bivalves, and they are usually found buried just below the surface or up to two feet under sandy or muddy freshwater or ocean bottoms.
Clams filter water for breathing and food through two different siphons, inhalant and exhalant. The inhalant siphon takes in water and food particles. The exhalant siphon releases water with waste.
Species of clams range widely in size. The largest species, appropriately named the giant clam, has been found to reach widths of 5 ft and weights of 500 lbs.
Species of clams range widely in size. The largest species, appropriately named the giant clam, has been found to reach widths of 5 ft and weights of 500 lbs.
Major Internal and External Anatomy
Growth rings: mark the stage of development or age of the clam
Umbo: the point on the shell at which growth begins; marks one of the earliest stages of development
Hinge ligament: helps the shell open and close at the meeting of the two shells
Posterior/anterior adductor muscle: bridges the gap between the halves of the shell to hold them together
Mantle: membranous tissue that covers entire body; yellow/cream color, secretes shell material
Gills: folded, ridged tissue with microscopic cilia; aids in respiration and the gas exchange
Foot: hatched-shaped and hard, provides locomotion and movement to the organism
Labial palp: leaflike structures between gills and anterior adductor that direct water carrying food into the mouth
Inhalant/exhalant siphons: folds in the mantle that regulate flow of water into and out of the clam
Mouth: slit between palps that is the site of the passage of food into the digestive system
Digestive gland: light green mass surrounding stomach that secretes enzymes into the digestive system
Anus: end of intestine near exhalant siphon; removes undigested food
Reproductive organ: spongy reddish mash ventral to the palps that produces eggs and sperm in clams of their respective genders
Intestine: coiled tubule from stomach through body to anus; site of the absorption of digested food
Incision Guide
At the dorsal end of the clam, there is a hinge ligament that needs to be cut before the clam is cracked open. There should be care not to go too deep, however, because the heart is in close proximity in the interior of the clam.
Once the clam is cracked open, mantel should be pulled away to view the inhalant and exhalant siphons.
There may be some difficulty in cutting open the tough muscle of the foot to reveal the reproductive organs, stomach, and digestive gland. The intestine is mostly in the foot but partially out of it, and the anus follows it.
Once the clam is cracked open, mantel should be pulled away to view the inhalant and exhalant siphons.
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