Caecum intortum sp. n.

Figs 6A–F, 7, 22J, 23J, 24C, D, 25Q

Etymology: From the Latin adjective intortus (= twisted) due to the twisted shape of the tube.

Description: Tube cylindrical, only slightly arched. The tube shows a clear dextral torsion. Tube smooth without sculpture, colourless, dull. Aperture preceded by a slight swelling. The aperture is oblique in both ventral and lateral direction, being contracted on the left side. Surface with only oblique, fine growth lines. Septum dome­shaped, granulated, with a broad nail-like mucro directed toward the right side. Macula large, ill­defined, expanded, with a frosted appearance, clearly displaced to the left side. Juveniles rather different from adults, more conical and showing a clear dextral torsion. Larval stage not determined with certainty, probably with a multispiral protoconch. Periostracum light brown. Operculum, corneous, circular, multispiral, composed of a small central nucleus surrounded by an open spiral of 6­7 whorls. External side flat, internal side with a concave nucleus.

Length: 1.9–2.6 mm.

Type locality: SOUTH AFRICA: Western Cape: Walker’s Point, west of Knysna.

Holotype (Figs 6A–C, 22J, 23J): SOUTH AFRICA: Western Cape: sh, Walker’s Point, W of Knysna, leg. J.P. Marais iii.1991, (NMSA W9668 / T3358), length 2.12 mm, min. diam. (posterior end) 0.38 mm, diam. in the middle of the tube 0.45 mm, max. diam. (apertural end) 0.49 mm.

Paratypes: SOUTH AFRICA: Western Cape: 2 sh, Hermanus (between False Bay and Cape Agulhas), v.1990 (JPM) ; 1 lv, Walker’s Bay, W of Knysna, iii.1991 (JPM) ; 4 sh, Knysna, Gericke Point, Sedgefield (NMSA W9670 / T3361) ; 2 lv and 8 sh, same data as holotype (NMSA W9669 / T3360); Eastern Cape: 1 sh, Algoa Bay, vi.1976 (JPM) ; 1 sh, Algoa Bay, Humewood sand, don. F. Graeve v.1977 (NMSA W9667 / T3359) .

Additional material examined: SOUTH AFRICA: Eastern Cape: 1 sh (juv), Port Alfred, (J. Hutt colln, ex Albany Museum, 1980) (NMSA W9666) .

Comparative material examined: C. crassum de Folin, 1870, lectotype (MNHN-IM-2000-27586) selected by Linden & Moolenbeek (2000: 82, fig. 3); SENEGAL: 8 sh, Gambia, ­ 7 m (F. Swinnen colln, Lommel, Belgium) ; MAURITANIA: 1 lv + 34 sh, Banc d’Arguin, intertidal, leg. E. Rolán (MP) ; GABON: 2 sh (1 juv) (MP) .

Distribution: Southern coast of South Africa from Hermanus to Algoa Bay (Fig. 7).

Remarks: The species most similar to Caecum intortum is C. crassum de Folin, 1870 (Fig. 25S,T), an endemic species of western African coasts (from West Sahara to Ghana), having in common the general shape of the tube and the typology of the septum, but differing in the smaller dimensions and in the exasperate torsion of the tube not observed in C. crassum . Additionally, C. intortum shows a different shape of the macula, which is also clearly displaced toward the left, and lacks the longitudinal microsculpture that is observed in C. crassum (van der Linden & Moolenbeek 2000) . Caecum intortum resembles both C. austrafricanum sp. n. and C. knysnaense sp. n., from which it can be separated by a wider tube, a more cylindrical shape, a clearly twisted tube and the position of the mucro, lateral rather than dorsal.