Glaucus, a genus of nudibranch Gasteropods, inhabiting the warmer parts of the Atlantic and
Pacific oceans. The body is long, slender, gelatinous, furnished with three pairs of lateral outgrowths with numerous fine processes. The mouth has the usual horny jaws, adapted for preying on other small marine animals; the antennæ or 'horns' are inconspicuous. These small molluscs—about an inch and three-quarters long, of a blue colour, and extremely delicate and beautiful, float inertly with irregular movements of their slender appendages on the surface of the water. For the nature of the outgrowths, &c., see NUDIBRANCHS.