| Plesiocystiscus gutta, Plesiocystiscus josephinae|
Cystiscus is a taxonomic genus of minute sea snails, marine gastropod mollusks or micromollusks.
This genus was placed in the family Cystiscidae by Coovert and Coovert, 1995. Previously the genus was in the family Marginellidae, where it is still placed by many other malacologists.
Shell minute to small, white, hyaline; spire immersed to low; lip thickened, smooth or weakly denticulate; external varix absent; siphonal notch absent; posterior notch absent; lacking collabral parietal callus ridge; columella multiplicate, with combined usually 2 to 8 plications plus parietal lirae, first plication usually strong and raised. Mantle smooth, at least partially extending over external shell surface.
The type species of this genus is Cystiscus capensis Stimpson, 1865
Shell minute to small (adult length 1–6 mm). Color white, hyaline; surface smooth, glossy. Shape usually elliptic, obovate, or subtriangular; weakly shouldered. Spire completely immersed to low. Aperture narrow to broad, usually wider anteriorly. Lip slightly to distinctly thickened, flared posteriorly in some species, smooth on inside edge to weakly denticulate, lacking lirae, external varix absent. Shell lacking a siphonal notch and posterior notch. Shell with weak parietal callus wash or weak parietal callus deposits in some species, but lacking collabral parietal callus ridge. Columella multiplicate, with combined total 2 to 8 plications plus parietal lirae, rarely to 17 in which the posteriormost are denticles; one species with only 1 plication. Plications usually occupying less than half the length of the aperture, but most of the aperture in some. Plications excavated just inside aperture in a few species, usually evenly rounded, first plication usually raised and very strong. Shell with cystiscid internal whorls.
External: Animal with eyes at side of head, usually on lateral swelling; mantle smooth, at least partially extending onto external shell surface, in some species nearly covering shell; foot relatively narrow, about as wide as shell length; head and mantle usually uniformly colored, often bright red, orange, or yellow, or brown, or black, internal mantle color pattern often showing through translucent shell.
Radula: Uniserial, ribbon long, narrow, composed of 80-209 plates. Rachidian plates overlapping, narrow, moderately to strong arched, with 6-14 sharp cusps on posterior edge, the central cusp usually the strongest. The anterior edge of the rachidian plate is strongly concave, resulting in U- or V-shaped plates.
Intertidal to 370 m.
Eocene of France and Alabama, upper Oligogene and Miocene of Western Atlantic, to Recent.
The two halves of the head are capable of closing together at will, thus appearing unsplit. The long siphon usually distinguishes this group from Gibberula. The shell of Persicula is usually patterned, often has a distinct external varix, and the spire is usually immersed. These conchological features serve to separate the two groups.Cystiscus alternans Pritchard & Gatliff, 1899
Cystiscus angasi Crosse, 1870
Cystiscus aphanacme (Tomlin, 1918)
Cystiscus bucca Tomlin, 1916
Cystiscus capensis Stimpson, 1865 T
Cystiscus connectans May, 1911
Cystiscus cratericula Tate & May, 1900
Cystiscus cymbalum Tate, 1878
Cystiscus flindersi Pritchard & Gatliff, 1899
Cystiscus freycineti May, 1915
Cystiscus goubini Bavay, 1922
Cystiscus halli Pritchard & Gatliff, 1899
Cystiscus huna Kay, 1979
Cystiscus incerta May, 1919
Cystiscus indiscreta May, 1911
Cystiscus japonicus (Nomura & Hatai, 1940)
Cystiscus jucundus (Turton, 1932)
Cystiscus manceli (Jousseaume, 1875)
Cystiscus melwardi Laseron, 1957
Cystiscus minusculus Lussi & Smith, 1998
Cystiscus minutissima Tenison Woods, 1876
Cystiscus obesula May, 1919
Cystiscus ocellus (Dall, 1927)
Cystiscus opima Laseron, 1957
Cystiscus peelae Lussi & Smith, 1998
Cystiscus problematica Gatliff & Gabriel, 1916
Cystiscus pseustes (E.A.Smith, 1904)
Cystiscus sandwicensis (Pease, 1860)
Cystiscus subauriculata May, 1916
Cystiscus thouinensis May, 1916
Cystiscus tomlini Bavay, 1917
Cystiscus tomliniana May, 1917
Cystiscus vidae Dell, 1956