Tricolia saxatilis, Nangammbi & Herbert, 2006

Nangammbi, T. C. & Herbert, D. G., 2006, Two new species of Tricolia Risso, 1826 from South Africa (Mollusca: Gastropoda: Phasianellidae), African Invertebrates 47, pp. 11-11 : 17-21

Tricolia saxatilis sp. n.

Figs 17–28

Etymology: saxatilis (Latin) – found among rocks.

Diagnosis: Shell small and thin, turbiniform with low-spire and globose outline; whorls well rounded, suture strongly indented; sculpture of fine raised spiral threads; umbilicus open, coloration variable, usually axially patterned in shades of red or brown on a whitish or pinkish ground; operculum granulate, with a deep pit at nucleus.

Description ( Figs 17–20 ): Shell small and thin, turbiniform with globose outline and relatively low, rounded spire; teleoconch of up to 2.25 whorls with strongly indented suture. Sculpture of fine raised spiral threads. Aperture sub-circular; umbilicus open, with a distinct channel behind inner lip leading to umbilicus. Shell somewhat translucent, coloration variable; ground colour frequently pinkish-white to dark pink or maroon, rarely tinged with amber; frequently with alternating reddish and white spots below the suture and at periphery of last adult whorl ( Figs 17, 18 ), or with reddish axial stripes on a white ground ( Fig. 19 ); body whorl occasionally almost uniformly white and apical whorls dark red-brown ( Fig. 20 ); base frequently with a broad, reddish spiral band, separated from umbilicus by a similar whitish band.

Dimensions: Holotype ( Fig. 17 ), length 2.04 mm, width 1.70 mm (= largest specimen); l/ w 1.0 –1.4, a/l 0.5–0.6 (N=50).

Protoconch ( Figs 21, 22): Typically trochoidean, comprising approx.1.25 whorls; apical beak present but very weak, terminal lip lacking a varix and with no mid-whorl angulation; sculptured with very fine spiral lines.

Operculum ( Fig. 23): Calcareous, thick and convex; paucispiral with eccentric nucleus; external surface with deep pit at nucleus and relatively coarse, irregularly granulate sculpture, and with a narrow, but distinct peripheral groove underlying labral margin.

[Available in colour at http://www.africaninvertebrates.org.za] Radula ( Figs 24–26): Similar to T. adusta sp. n., but denticles on cusps of innermost laterals more or less equal in size.

External anatomy ( Fig. 27 ): Typically trochoidean, but differs from most Tricolia species in the form of the neck-lobes – left neck-lobe broad with ±5 digits, right neck-lobe broad and smooth; middle epipodial tentacle much smaller than the other two, with no sense organ evident at its base.

Geographical range ( Fig. 28 ): Endemic to South Africa, ranging from northern KwaZulu- Natal (Zululand) to Eastern Cape (Port Alfred).

Habitat: A subtidal species inhabiting off-shore reefs; living specimens 8–36 m, empty shells to 50 m.

Holotype: SOUTH AFRICA: Eastern Cape: NMSA, V4048 /T2129, off Whale Rock (31 o 56.9'S: 29 o 13.5'E), 20–26 m, sand and gorgonians, dredged NMDP, 16.vii.1982.

Paratypes (all NMSA): SOUTH AFRICA: Eastern Cape: W4299/T2215 (3), same data as holotype. KwaZulu- Natal : E7144/T2128 (11), Aliwal Shoal, Cracker Reef, approx. 23 m, living, dived D. Herbert, 30.iv.1989 ; W2585/T2127 (33), Aliwal Shoal (30.26690 oS:30.82302 oE), approx. 15.5 m, loose rubble, living, dived ORI, 07.xii.2004 ; W2582/T2125 (8), Aliwal Shoal (30.26017 oS:30.82775 oE), ± 8 m, loose rubble, living, dived ORI, 09.xii.2004 ; S6773/T2124 (52), Aliwal Shoal , 10–20 m, sand, dived D. Herbert, 30.vi.1991 ; S8662/T2119 (61), Aliwal Shoal , approx. 14 m, underwater pump, dived D. Herbert, 02.vi.1991 ; S8215/ T2120 (52), Aliwal Shoal , 10 m, sand and reef debris, hand-dredged, D. Herbert, 04.iv.1992 ; W2717/T2126 (1), off Phumula (30 o 38.279'S: 30 o 32.918'E), approx. 36 m, low profile reef, living, dived M. Wallace & V. Fraser, 07.xii.2004 .

Additional material examined (all NMSA): SOUTH AFRICA: northern KwaZulu-Natal: off Hully Point (27 o 20.2'S: 32 o 46.2'E), 40 m, very fine muddy sand, algae, dredged R.V. Meiring Naudé, 05.vi.1987 (E1458); central KwaZulu-Natal: off Park Rynie, 50 m, coarse sand, ex CSIR Water Research (B5666); Aliwal Shoal, ± 16 m, hand-dredged sand, dived D. Herbert, 26.v.1990 (S5992); same data, 9–15 m, dived D. Herbert & R. Emanuel, 27.xi.1988 (E6197, E6273); Aliwal Shoal, approx. 20 m, hand-dredged sand, dived D. Herbert, 25.x.1992 (S7920); Aliwal Shoal, 25–27 m, sand and reef debris, hand-dredged D. Herbert, 04.iv.1992 (S7158);Aliwal Shoal, off Umkomaas, 25–28 m, hand-dredged sand, dived D. Herbert, 16.xii.1990 (S9881). Eastern Cape: off Mbotyi (31 o 29.2'S: 29 o 45.4'E), 50 m, sand, dredged R.V. Meiring Naudé, viii.1981 (E185); off Port Alfred (33 o 42'S: 26 o 56'E), 65 m, ex gut Congiopodus torvus , leg. D. Herbert on R.V. Africana , 3.v.1997 (V5161).

Taxonomic comparison: In comparison with all other species of Tricolia occurring in southern Africa, T. saxatilis is smaller, lower-spired, has more convex whorls, and a more distinct umbilicus. In its globose shape and small size, T. saxatilis resembles T. deschampsi Gofas, 1993 , T. entomocheila Gofas, 1993 , T. nordsiecki (Talavera, 1978) , T. punctura Gofas, 1993 , and T. tingitana Gofas, 1982 , from the Mediterranean. It differs notably from these, however, in its coarsely granular, pitted operculum.

Figures

Figs 17–20. Tricolia saxatilis sp. n., variation in shell colour and pattern: (17) holotype, length 2.04 mm, width 1.70 mm, NMSA V4048/T2129; (18–20) paratypes: (18) length 1.42 mm, width 1.19 mm, NMSA E7144/T2128, (19) length 1.79 mm, width 1.48 mm, NMSA S6773/T2124, (20) length 1.64 mm, width 1.32 mm, NMSA E7144/T2128.

Fig. 27. Tricolia saxatilis sp. n., external anatomy: ct – cephalic tentacles; eso – epipodial sense organ; et – epipodial tentacle; lnl – left neck-lobe; rnl – right neck-lobe.

Fig. 28. Tricolia saxatilis sp. n., distribution map. Each black triangle represents one site record.