The present small species is readily recognized by its strong, prominent spirals and small aperture. Iravadia gardnerae Ladd, 1966, described from Late Miocene and Pliocene deposits of Bikini and Eniwetok, appears to be closely related and may prove to be a junior synonym.

Shell rather small (up to 4.2 mm, N = 33), elongately to broadly conical, stout. Protoconch of planktotrophic larval type ; broadly conical, of 2 1/2 wide, low and convex whorls; last whorl with a centrally located carina, the latter becoming gradually more prominent towards transition to teleoconch ; transition abrupt with a deep sinusigeral notch. Teleoconch of 3 1/2 to 4 3/4 whorls ; sutures rectilinear, barely impressed. Sculpture of very prominent, wide, rounded spiral ribs, with deep and slightly wider interspaces; spiral ribs numbering 2 on first whorl, 3 to 4 on subsequent spire whorls and 6 to 7 on last whorl; abapicalmost spiral rib of spire whorls partly covered by suture of next whorl in some specimens. Interspaces between spiral ribs with fine, moderately distantly spaced axial threads. Aperture ovate ; inner lip thin, moderately expanded ; anterior channel shallow, very narrow, very short; outer lip thin internally, sometimes with elongate ridges, the latter corresponding to spiral ribs on varix of outer lip; posterior channel absent; outer lip externally with a thick and wide varix, the latter bearing very prominent spiral ribs ; outer lip very weakly opisthocline in profile. Shell colour: glossy white. There is considerable interpopulation variation with respect to the shell dimensions, but otherwise no marked variation in shell shape or sculpture was observed amongst the rather extensive series of specimens examined.

Stosicia annulata is readily distinguished from its congeners by the combination of the following characters : (1) the absence of axial ribs and (2) the presence of very prominent spiral ribs. The axial sculpture is also absent in S. bougei (BAVAY, 1917), but the spiral ribs are less prominent and much more densely spaced in the latter species.
S. annulata is superficially similar to an unidentified spirally ribbed Indo-Pacific pyramidellid species, but is easily distinguished by the different protoconch and in lacking the columellar fold.

Stosicia annulata is distributed in the Indo-Pacific, from the Persian Gulf to Japan. It is reported to occur in the intertidal and shallow infralittoral zones on sand, shell sand and gravel (HABE, 1968; HASEGAWA in OKUTANI, 2000).

Indian Ocean, Borneo and China coast

Indian Ocean, Borneo and China coast