Collonista imperforata
Collonista imperforata is a species of small sea snail with calcareous opercula, a marine gastropod mollusk in the family Colloniidae.
Description
The diameter of the shell attains 3.5mm, its height 3.05mm.The shell is small, globose, imperforate when adult, and thick. It features a spirally costate sculpture. The color is yellowish-white, with the spiral ribs maculated with brown. The spire is depressed, sitting lower than the aperture.
The sculpture consists of prominent, nodulous ribs, with the nodules being rather low. There are two ribs on the penultimate whorl and six on the body whorl. A small nodulous rib appears on the last half of the body whorl close to the suture, followed by four equally strong, equidistant spiral ribs. The interspaces are much broader than the ribs. The whole surface is crossed by fine, close, oblique incremental striae. A sixth broad rib, more nodulous than the others, forms a semicircle around the strongly impressed umbilical area. This area is itself ornamented with distant axial folds.
The protoconch is white, consisting of two spirally costate flat whorls. There are four whorls total, with the last being large, flattened below the suture, and then convex; the base is rounded. The suture is not impressed.
The aperture is oblique, nearly circular, white, and porcellanous inside. The peristome is thick, very little contracted, crenulated on the outside by the spiral ribs, and regularly convex. The columella is arcuate, shining, white, and thick. The inner lip spreads over the umbilicus, completely sealing it up, or sometimes leaving a minute chink. A white callus unites the converging margins of the peristome. In young specimens, the umbilicus is open, but very narrow. The operculum was not seen.