Q:

What items could you put into a dichotomous key to tell different types of sharks apart?

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Quick Answer

A dichotomous key for sharks may include body shape, presence of a pelvic fin, number of gill slits or dorsal fins, mouth position, head shape, length of dorsal fin or caudal fin, presence of an anal fin, hornlike appendages near the head and special markings on body. Each dichotomous key differs depending on the species of sharks included.

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Full Answer

When viewed from above, sharks have different body shapes. Some look like diamonds, whereas others are more elongated. Shark families that have a diamond body shape include the families Rajidae, Mobulidae, and Dasyatidae. Certain features belong specifically to one family of sharks. For example the family Pristiophoridae is the only shark family that carries a saw-like, elongated nose, and six gill slits are present in the family Hexanchidae.

The number of gill slits is the easiest feature to identify. Water passes over the gills while the shark is swimming, allowing oxygen to diffuse into the blood. Bony fish have only one gill slit, whereas sharks have five to seven, depending on the species.

Sharks eat a variety of food including plankton, mussels, mollusc, fish, birds and marine mammals. Observing a shark's diet is another factor to use to help identify the specific type of shark. Sharks inhabit almost all areas of the world's oceans.

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