Shell small, of porcellain-like structure, spirally coiled, roundish, lens-or low top-shaped, with a few (2-5) more or less rapidly-increasing whorls, frequently with lattice-like sculpture, rarely smooth, in most cases widely umbilicate; from the apertural margin arises a slit, with an associated more or less long slit band, or the end of the slit is closed, so that it becomes a longer or shorter hole. Operculum horny, with several whorls.

Mantle of the animal cleft; under each lobe lies a bipectinate gill: above the foot in the epipodial line there are a few tentacles without distinct longitudinal folds. The nervous system in the foot is fairly concentrated; the shell muscles, the kidneys, and the auricles are paired; the ventricle is traversed by the intestine. Central plate of the radula posteriorly broadened, with sharp denticulate cutting edge; with 5 intermediate plates, the four inner of which form an oblique forwardly directed row decreasing in size outwardly and their cutting edges are denticulate; the outermost plate is larger, and its cutting edge is also denticulate, as is that of the numerous long and narrow lateral plates.

Scissurellidae is a relatively obscure family of gastropods and at present is of uncertain phylogenetic placement. Scissurellids are found in all oceans, from shallow intertidai waters to the abyss (Hickman 1998a; Geiger and Jansen 2004). Scissurellids are diagnosed by their tiny size, usually 1 to 6 mm; a slit or foramen, and related selenizone found associated with the anal fasciole; rhipido-glossate radula with a serrated rachidean tooth; and retention of paired ctenidea and hypobranchial glands. Scissurellids are tiny, relatively fragile snails that do not produce interior nacre. The single horseshoe-shaped columellar muscle is due to the fusing of 2 shell muscles (Hickman 1998a). Shells are typically translucent and not pigmented and are characteristically ornamented with cancellate or axial sculpture. The protoconch ranges from smooth to sculptured with the terminal lip of the protoconch typically thickened. The position of the slit may be at the periphery of the shell to high on the shoulder of the shell. In contrast to the outer lip of the similar shell of the seguenziid gastropods, the slit is narrow and deep. The umbilicus may be either open or closed, and the inner lip may congeal into an umbilical cord (Hickman 1998a). Shell modifications are clearly present within this family. In some taxa the closure at the terminal end of the slit provides for an elongate to round foramen on the shell. Secondary bilateral symmetry, expansion of the aperture, and the limpet form have occurred in the hydrothermal-vent scissurellids. Shallow-water scissurellids are found associated with marine plant life (Hickman 1998a; Geiger 2003). In Texas Scissurellidae is represented by 2 genera and 3 species whose size is about 1 mm.

Family SCISSURELLIDAE Minute turbinate shells, umbilicate; porcelaneous except for a thin nacreous layer; lip with a slit or foramen; operculum multispiral. The species of the eastern Pacific were reviewed by McLean (1967). Two Panamic genera. Genus SCISSURELLA ORBIGNY, 1824 Shell with an open slit on outer lip, its trace on earlier whorls preserved as a slit band or selenizone. No species of subgenus Scissurella, s. s., occur in the Panamic province. Subgenus ANATOMA WOODWARD, 1859 Spire elevated, selenizone at the periphery, sculpture cancellate. Two recently described species are the first records of the group in the Panamic province.