On dating stages in prebiotic chemical evolution

This name is not repeated under each Species Account. This genus is characterised by an elongate and compressed body, a usually bifid, erectile spine below the eye (sometimes hidden under the skin), 3 pairs of short barbels (4 at the snout tip and 2 at the mouth corners), minute scales cover the body (as many as 200 but they are seldom counted accurately), lateral line faint or indistinct, dorsal and anal fins small, caudal fin rounded or truncate, and swimbladder in a bony capsule with a free portion visible.Males have bony extensions of their pectoral fin rays, known as lamina circularis or scale of Canestrini, and no swellings of their body sides.

Some members of this family can live in oxygen-poor waters.Foods are mostly small insects, worms and crustaceans detected by the aid of the barbels on the habitat bottom. Most species bury themselves in sand or mud during the day, emerging to feed at night.Movement is by undulations of the body, particularly marked in the more elongate species.Menon (1992) considers that structural details of the bony covering of the swimbladder and the nature of the scales are only of use at the generic level.Lip structures, fin positions relative to one another and secondary sexual characteristics in males are important characters in differentiating species in India.

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