Cerithium (Triforis) hebes 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 (Triforis) hebes Watson, 1880

Figure 115

Cerithium (Triforis) hebes Watson 1880: 103, not illustrated. Illustration available in Watson (1886): 551, pl. XLIII, fig. 7.

Type locality.

"Nightingale Island, Tristao da Cunha Islands, S. Atlantic"

Type material.

Syntypes: NHMUK 1887.2.9.1763-5: 3 specimens, type locality .

Original description.

St. 135. Oct. 18, 1873. Nightingale Island, Tristao da Cunha Islands, S. Atlantic. 100-150 fms. Rock; shells.

Shell.- Cylindrically conical, blunt, uncontracted towards the base, strong, translucent, hardly glossy. Sculpture. Longitudinals-on the last whorl there are about 20 longitudinal rows of rounded tubercles, parted by depressions of much the same breadth and form as themselves; they run more or less continuously and straight up the spire from whorl to whorl. There are indistinct lines of growth. Spirals- on each whorl the tubercles are arranged in three spiral rows, parted by rather deep but narrow squarish furrows. The highest row is rather smaller and less prominent than the others. The base of each whorl is sharply but not deeply constricted; the edge of this constriction appears on the margin of the base as a rounded thread, defined by a slight furrow, which, with the exception of microscopic radiating lines of growth, is the only ornament of the flat and very slightly conical base. Colour pure somewhat translucent white. Spire high and conical, but contracting very little, and hence more cylindrical than usual. Apex very blunt, but almost mucronated; this arises from the three embryonic whorls, which are smooth, being formed of two tumid threads, of which the lower is the larger, but the upper is at first the more prominent, and at its origin stands up minute, round, and prominent, like a small eccentric blunt spike, reminding one of the mucronated mamillary plug of some of the Caecums. It is not a plug, however, but the true embryonic form. This embryonic shell is smooth and glossy, but has some faint trace of spiral sculpture. Whorls 12, of very gradual increase, flat on the sides, constricted below, flat and hardly conical on the base. Suture well defined by the contraction of the whorl above it, and by a minute thread on which it projects. Mouth angulately oval, with a small straight canal in front. Outer lip broken. Pillar perpendicular, straight, short, narrow, pointed. Inner lip a thickish porcellanous glaze. H. 0.24. B. 0.06. Penultimate whorl 0.03. Mouth, length 0.032, breadth 0.02.

This species has some resemblance to T. suturalis, Ad. & Rve., but is easily distinguished from that by its blunt apex and the less sunken suture.

Diagnosis.

Syntypes ranging in height between 3.7 and 5.3 mm; none looks fully mature. Shell conical with slightly curved sides. The largest specimen has ca 9 whorls bearing three strong spiral cords from the beginning of the teleoconch; tubercles are present at the intersection with the orthocline axial ribs. A fourth smooth narrow cord is visible suprasuturally. Growth lines are visible between the cords. Due to the subadult stage, the peristome and the base are not fully developed. Siphonal canal short. The large protoconch is certainly paucispiral, with two whorls: the first bears a strong spiral keel and possibly some thick axial ribs, but all syntypes have very worn apexes. Teleoconch and protoconch white.

Figures

Figure 115. Cerithium (Triforis) hebes Watson, 1880, Nightingale Island, Tristan da Cunha, South Atlantic. A, K Original figures. B-F, J Syntype NHMUK 1887.2.9.1763: front (B, C), side (D, E), back (F), protoconch (J). G-I Syntype NHMUK 1887.2.9.1764: front (G), side (H), back (I). M-Q Syntype NHMUK 1887.2.9.1765: front (M, N), side (O), protoconch (P, Q). L Original labels. Scale bars: B-I: 1 mm; H, P, Q: 0.2 mm; M-O: 0.5 mm.