Dorsal

From Palaeos.org

Dorsal from the Latin dorsum, the back, refers to the upper surface or back of the body of a bilaterian animal, which faces upward when it is swimming, crawling, walking, or flying.

For example the dorsal fin of a shark, ichthyosaur, or dolphin is a proiminant fin in the middle of the back that aids in stabilising the animal in the water.

In a bivalve, dorsal refers to the back edge or top of a bivalve, in the region of the hinge. The "dorsal margin" therefore in bivalves refers to the hinge region.

In echinoderms, dorsal has a number of different meanings. In crinoids, it is the side of the body opposite the mouth and in most species bearing the stem attachment, even though ironically it is functionally on the ventral (lower) side. In asteroids, ophiuroids and echinoids it refers to the surface of the body that is opposite the mouth, and hence is positioned uppermost. In holothuroids, in which the mouth and anus at opposite ends of a cylindrical body, the uppermost surface is considered dorsal, as in bilateral animals.

Dorsal is the opposed to ventral.

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