Zoom Sharks SHARK ANATOMY

GENERAL ANATOMY

Sharks are fish that have no bones, only cartilage. They have 5-7 gills (without gill covers, operculum) in front of their pectoral fins (on both sides). Shark tails are asymmetrical; the top lobe of tail is larger than the bottom lobe. The shark's jaw is not fused to the braincase and can enlarge to eat very large prey. Sharks have no swim bladder for buoyancy (like the bony fishes); an oily liver aids buoyancy. Sharks have an advanced electroreceptive system that detects slight electrical fields.

The teeth and skin are modified placoid scales. A spiracle (a special gill slit that supplies oxygen directly to the eyes and brain) is present in front of the first gill. Sharks' teeth are replaceable when they've broken or worn out. Their intestines are short and compact and have an unusual structure; a spiral valve (shaped like a spiral staircase) fills the cylindrical intestines and allows absorption of the food in a short span of intestine.

MAJOR DIFFERENCES BETWEEN SHARKS AND BONY FISH

ATTRIBUTE	SHARKS	BONY FISH
Skeleton	Cartilage only	Bones and cartilage
Swimming	Can only swim forward.	Can swim forwards and backwards
Buoyancy (floating)	Large oily liver	Gas-filled swim bladder
Gills	Gill slits but no gill cover	Covered gill slits
Reproduction	Eggs fertilized in female's body.	Eggs usually fertilized in the water.
Skin	Rough, sandpaper-like placoid scales	Slippery, overlapping scales

Zoom Sharks SHARK ANATOMY

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