Clanculus microdon

Clanculus microdon is a marine gastropod mollusk in the family Trochidae, commonly known as a top snail. Its shell, which can reach 17 mm in size, is thick, solid, and depressed-conoidal in shape. The shell is reddish-brown, with chocolate-colored spaces between the ribs. On the upper surface, a few broad yellowish or flesh-tinted blotches radiate from the sutures toward the periphery but do not reach it; the periphery and base have ribs sparsely dotted with white. The spire is low-conic with a roseate apex, and the suture is distinct but not canaliculate. The five whorls are moderately convex and encircled by about 14 lirae on the body whorl; these lirae are unequally sized and more or less distinctly granulate. The interstices are closely obliquely striate and usually have a minute central riblet. The body whorl descends anteriorly and is rounded at the periphery. The base is convex, with revolving lirae that are broader, flatter, and more finely granulated than those on the upper surface; these number 6 to 7, with one or two around the umbilicus. The umbilicus is white, dotted with yellow or reddish, while the rest is reddish-brown with sparse white articulation on the ribs, sometimes with narrow white radial stripes. The aperture is oblique, somewhat contracted, and subcircular; the outer and basal lips are thickened and finely crenulated inside. The columella is oblique, with a tooth-like fold above, and is deeply inserted on the side of the umbilicus. Its middle portion is concave with a reflexed, subdenticulate edge that ends in a minute denticle below. The deep umbilicus is smooth and polished inside, bordered by a strong rib bearing 6 or 7 projecting white teeth, the uppermost being the largest.

This species belongs to a group that includes *Clanculus atropurpureus* and *Clanculus bathyrhaphe*, among others. In this group, the base of the columella is scarcely toothed and passes into the basal margin in a regular curve, bearing several subequal denticles. The columella is inserted on the side of the umbilicus rather than in the center of the axis, as in typical *Clanculus* (subgenus *Clanculopsis*). Compared to its nearest ally, *Clanculus atropurpureus*, *Clanculus microdon* is larger, has variegated coloration, and has irregular spiral ribs on the upper surface.

The variety *Clanculus microdon* var.