Eyespot rasbora ventral area of the body between the operculum and the pelvic fins (corresponding roughly to the sac enclosing the alimentary canal). Under conditions of reflectied light, the fish sometimes displays a fine lateral band from the opeculum to the end of the caudal peduncle (Walker, 1971, p. 98) this being an olive-gold hue. The fins, with the exception of the dorsal fin, are hyaline, the relation of the pectoral and pelvic fins being typical of the ostariophysans (fishes possessing an auxiliary mechanism for detecting sound consisting of a set of internal bones called the Weberian Ossicles). In such fishes, the
Operculum (gastropod) shell when the soft parts of the animal are retracted. The shape of the operculum varies greatly from one family of gastropods to another. It is fairly often circular, or more or less oval in shape. In species where the operculum fits snugly, its outline corresponds exactly to the shape of the aperture of the shell and it serves to seal the entrance of the shell. Many families have opercula that are reduced in size, and which are not capable of closing the shell aperture. Opercula have sometimes been modified: in the Strombidae the operculum is claw-shaped and is used