Cerithium (Bittium) abruptum Watson, 1880

Albano, Paolo G., Bakker, Piet A. J. & Sabelli, Bruno, 2019, Annotated catalogue of the types of Triphoridae (Mollusca, Gastropoda) in the Natural History Museum of the United Kingdom, London, Zoosystematics and Evolution 95 (1), pp. 161-308 : 161

Cerithium (Bittium) abruptum Watson, 1880

Figure 113

Cerithium (Bittium) abruptum Watson 1880: 119-120, not illustrated. Illustration available in Watson (1886): 551, pl. XLI, fig. 4.

Type locality.

Lat. 38°38'N, long. 28°28'30"W, Fayal, Azores.

Type material.

Syntypes: NHMUK 1887.2.9.1709-11: 3 specimens, type locality .

Original description.

St. 75. July 2, 1873. Lat. 38°38'N., long. 28°28'30"W. Fayal, Azores. 450-500 fms. Sand.

Shell.- Small, narrow, conical, blunt, in general form very like a decollated Cerithiopsis metaxa, solid, translucent, white. Sculpture. Longitudinals-there are on the last whorl about thirteen, on the earlier, fewer longitudinal ribs, which are low and narrow, and are parted by flat and broader furrows. They come down the spire, from whorl to whorl, with a strong sinistral twist. The embryonic whorls have ten or twelve small ribs. Spirals-except on the first two whorls there are on each whorl four narrow, rounded, prominent spiral threads, which rise, as they cross the longitudinals, into pointed high tubercles. The furrows which part them (except that between the third and the fourth) are narrower than the spirals. The highest of these spirals is the weakest and least prominent, being pinched in by the superior contraction of the whorl into the suture. Close above this highest spiral runs the suture. The base of each whorl is roundly but rather abruptly contracted, so that the sutural furrow has its upperside abruptly, its underside gradually, declining. The base, which is oblique, concave, and contracted, has a strong plain spiral thread round its edge, and a very minute thread encircling the base of the pillar, the scar of the siphonal cut. Besides the larger systems of sculpture, there are some faint and irregular traces of microscopic rounded longitudinals and sharper spirals. Colour translucent white. Spire high, narrow, with very straight outlines, and scarcely contracted. Apex excessively blunt and abrupt, the extreme point being rounded and barely rising into view; it is quite smooth and polished. The second whorl is longitudinally ribbed and polished; on the third the ordinary sculpture begins. Whorls 11, convex, constricted suddenly below and gradually above. Suture excessively minute and faint in itself, but its place strongly marked by the constriction of the whorls above and below. Mouth very small, oval, perpendicular, pointed above, and with a large open rounded slit in front, whose edge is hardly reverted. Outer lip thin, advancing on the base much beyond the point of the pillar. Inner lip a thin glaze, with microscopic corrugations on the pillar. Pillar very short, with a broad base spreading out to meet the outer lip, straight, with a broad but sharp point. H. 0.23. B. 0.05. Penultimate whorl, height 0.03. Mouth, length 0.028, breadth 0.02.

This species in general aspect is very like Cerithiopsis metaxa, della Chiaje, but differs in not having the sharp sculptured apex; the whorls, in consequence of the sutural contraction, are more rounded; the longitudinals are swellings of the whole shell, not, as in that other, mere projecting tubercles; the spirals are more definitely continuous; the longitudinal rows of tubercles run less definitely from whorl to whorl, and have a strong sinistral twist as they proceed down the spire, while in C. metaxa their continuous lines are very straight.

Remarks.

Bouchet (1985) accurately described the species and, therefore, we refrain from adding additional diagnostic notes.

Figures

Figure 113. Cerithium (Bittium) abruptum Watson, 1880, Fayal, Azores. A, B, D, G, J, K Syntype NHMUK 1887.2.9.1709: front (A, B), side (D), protoconch (G), aperture (J), peristome (K). C Original figure. E, H Syntype NHMUK 1887.2.9.1710: front (E), protoconch (H). F Syntype NHMUK 1887.2.9.1711: front. I Original labels. Scale bars: A, B, D-F, J, K: 0.5 mm; G, H: 0.1 mm.