Bathylagoides wesethi very low on the underside of the body. The colour is dark brown above with black spots and a black patch around the operculum, which extends halfway up the body. The flanks are silvery-grey and the fins lack pigment. The caudal peduncle is narrow, the caudal fin is short, and the lateral line, which is high on the body, extends into the tail fin. The maximum length to which this fish grows is about . The snubnose blacksmelt is found in deep water in the Pacific Ocean off the western coast of North America. Its range extends from 45°N to
Operculum (gastropod) to push into the substrate in a leaping form of locomotion. Virtually all pulmonate snails are inoperculate, i.e. they do not have an operculum, with the exception of the Amphiboloidea. However, some terrestrial pulmonate species are capable of secreting an epiphragm, a temporary structure that can in some cases serve some of the same functions as an operculum. The epiphragm may be distinguished from the true operculum by its homogeneity and want of growth marks. In ammonites (extinct shelled cephalopods), a calcareous structure known as the aptychus (plural aptychi) existed. When these were first described they were thought to be