Common Name

"Biraghi’s Cone"

Status

Regarded as a valid species. Described as Thoraconus biraghii.

Type Locality

Obja, (600 kms) North of Mogadishu, Somalia

Distribution

Somalia

Maximum Reported Size

11,5 mm

Description

C. b. biraghii (very small and light. Last whorl broadly and ventricosely conical to broadly conical, sometimes ventricosely conical to conical in form A; outline convex adapically, less so to straight below; left side usually slightly concave at base. Shoulder angulate to carinate, smooth to usually undulate due to axial costae on subshoulder area, consistently smooth in form B. Spire usually of moderate height, stepped; outline almost straight. Postnuclear spire whorls weakly tuberculate to undulate due to axial subshoulder costae (form A) or consistently smooth (form B). Teleoconch sutural ramps slightly concave, with obsolete spiral striae. Last whorl with spiral grooves on basal fourth and 1-2 weak spiral grooves just below shoulder. C.b. congruens with an often less ventricose last whorl. Shoulder often irregularly undulate due to weak axial subshoulder costae. Spire high, stepped; outline straight to slightly concave. Larval shell of 2-2.25 whorls, with widely spaced fine radial ridges; maximum diameter about 0.8 mm. Postnuclear spire whorls usually smooth, sometimes irregularly undulate due to very weak axial subshoulder costae. Teleoconch sutural ramps concave, often with 1 increasing to 2-3 weak or distinct spiral grooves in early whorls; spiral sculpture obsolete on late ramps. Last whorl with spiral ribs basally and 1-2 distinct spiral grooves just below shoulder; subshoulder grooves may be visible in stepped preceding spire whorls. C.b. omanensis with an often narrower, ventricosely conical last whorl. Shoulder angulate. Larval shell of about 2 whorls, with fine radial ridges on final part. Teleoconch sutural ramps flat, with 1 increasing to 3 distinct spiral grooves pronounced also in late whorls. Spiral subshoulder grooves consistently visible in stepped spire whorls. C.b. omanensis otherwise matching C.b. congruens in morphology. Some shells of C.b. omanensis closer to C.b. biraghii due to concave teleoconch sutural ramps and prominent axial subshoulder costae.

In C. b. biraghii form A, ground colour white to grey. Last whorl with a broad dark grey to olive grey spiral band within adapical third and at base, edged with brown to blackish brown spots and interspersed with scattered to regularly arranged ground-colour spots. Ground-colour band below centre usually with an indistinct meshwork of white spots. Sparse spiral rows of brown dots between subshoulder area and base. Specimens of form B with lighter, bluish to brownish grey spiral colour bands, more prominently edged and overlain with dark brown spots; ground-colour band below shoulder narrower than in shells of form A, subcentral ground-colour band with a more indistinct pattern of white background spots. Spiral rows of brown dots and dashes often more prominent, sometimes extending to shoulder. Final part of larval shell white to pale beige, initial part eroded. Postnuclear sutural ramps with brown radial markings crossing outer margins. Aperture showing exterior pattern.

Shell Morphometry

L	9-12 mm
RW	0.01-0.04 g/mm
RD	0.68-0.80
PMD	0.77-0.91
RSH	0.12-0.19

Habitat & Habits

Shallow water on rocks.

Discussion

The colour pattern of C. b. biraghii suggests a "miniature" C. zonatus (G. Raybaudi Massilia, 1992). However, C. zonatus differs in its narrower last whorl (RD 0.55-0.64, likely lower in juveniles) and its third spiral colour band below shoulder. C. zonatus has prominently tuberculate postnuclear whorls without axial subshoulder costae. The holotype of C. traillii is similar in size and last whorl pattern. It can be distinguished by the more convex outline of its last whorl, its convex and immaculate postnuclear sutural ramps, rounded shoulder, and by the absence of axial subshoulder costae. The relationship between C. locumtenens and C.b. biraghii awaits further studies, when juvenile specimens of the former species become known.. The differences between C.b. biraghii form A and form B do not justify separation at the species level. C.b. omanensis was provisionally described as a geographical subspecies. This status seems to be justified by intermediate specimens occasionally occurring within the population from Masirah Id. C.b. congruens is conchologically more similar to C.b. omanensis than to C.b. biraghii.

References

• Acta Conchigliorum (3): p. 31, pl. 3, figs 16-22.