Tricolia adusta, 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 : 12-17

Tricolia adusta sp. n.

Figs 1–16

Etymology: adustus (Latin) – brown, referring to the predominately brown coloration of the shell.

Diagnosis: Shell small, elevated-turbiniform; whorls rounded, without any angulation, suture not strongly indented; smooth, lacking spiral sculpture and with only microscopic growth-lines; coloration highly variable, but typically buffish, patterned with zigzag brown axial lines and subsutural blotches, evidently never with pink dots on first two whorls or with bluish subsutural spots.

Description ( Figs 1–8 ): Shell small, elevated-turbiniform; teleoconch of up to 4.5 whorls with weakly indented suture; whorls smoothly rounded, lacking any angulation, periphery slightly below mid-whorl and profile usually more strongly curving below this than above; apex broadly rounded. Sculpture weak, shell mostly smooth and glossy, marked only by exceedingly fine growth-lines. Aperture sub-circular, outer lip thin, interior without nacre; colour pattern visible internally; inner lip concave and slightly reflected; umbilicus closed in most specimens, remaining as a narrow chink in others.

Coloration extremely variable, typically buff to pale yellowish-brown, variously marked with zigzag lines in shades of darker brown, frequently bolder below suture; umbilical region often bordered by a spiral band of alternating dark and light blotches ( Fig. 1 ); some specimens with large, dark brown to black, trapezoid blotches below suture ( Fig. 2 ); others with broad, alternating axial bands of brown and cream-white on apical surface ( Fig. 3 ); occasionally boldly patterned with close-set, red-brown to dark

brown, zigzag axial lines throughout ( Fig. 4 ); last adult whorl with apical surface sometimes almost uniformly whitish, red or dark brown ( Figs 5–7 ); rarely almost white throughout ( Fig. 8 ).

Dimensions: Holotype ( Fig. 1 ), length 3.30 mm, width 2.24 mm; largest specimen examined, length 4.43 mm, width 2.46 mm; l/ w 1.5 –1.8, a/l 0.4–0.5 (N=50).

Protoconch ( Figs 9, 10): Typically trochoidean, comprising approx.1.25 whorls; apical beak present but weak, terminal lip lacking a varix, but markedly angulate at mid whorl; sculpture for the most part smooth, with traces of curved lines towards periphery, and with raised vermiculate sculpture in apical region.

Operculum ( Fig. 11): Calcareous, thick and convex; paucispiral with eccentric nucleus; exterior with microscopic granular sculpture and a distinct peripheral groove underlying labral margin.

Radula ( Figs 12–14): Formula ∞ + 5 + 1 + 5 + ∞; transverse rows broadly M-shaped; rachidian tooth with broad, roundly-trigonal base-plate, lacking a cusp, but strongly overlapped by cusps of innermost laterals; base-plates of laterals overlapping extensively, the inner two with alate projections on outer margin; outermost lateral with trigonal base-plate and with a slightly smaller cusp than that of other laterals; cusp morphology of laterals somewhat variable between specimens; cusp usually with 2–4 larger central denticles and a variable number of small endocones and ectocones; one denticle frequently dominant on third and fourth laterals; innermost marginals (the first three or four) with a single broad spatulate cusp, with one strong ectocone and 1 or 2 smaller endocones; marginals progressively smaller toward edge of radula, the spatulate cusp becoming smaller and less distinct, and the ectocones finer and more numerous.

External anatomy ( Fig. 15 ): Typically trochoidean; neck-lobes well developed, both digitate; number of digits appears to be a function of specimen size; left neck-lobe broad and outspread with ±12 digits; right neck-lobe slightly smaller and with fewer digits. Three pairs of papillate epipodial tentacles on each side, the middle one somewhat smaller than the other two; an epipodial sense organ present at base of each tentacle; epipodial fold with light brown to purple-brown pigmentation, darkest between first and second epipodial tentacles. Foot longitudinally divided, sole white. Colour pattern of head-foot variable, resembling that of shell.

Geographical range ( Fig. 16 ): Endemic to South Africa, ranging from northern KwaZulu- Natal (Kosi Bay) to Eastern Cape (southern Transkei, Qora River).

Habitat: A subtidal species inhabiting off-shore reefs; living specimens from shallow infratidal to 70 m, empty shells from beach-drift to 140 m, exceptionally to 300 m.

Holotype: SOUTH AFRICA: KwaZulu-Natal: NMSA, E7143 /T2013, Aliwal Shoal, Cracker Reef, dived D. Herbert, 30.iv.1989, approx. 23 m, living.

Paratypes: SOUTH AFRICA: KwaZulu-Natal: NMSA, W2477 /T2014 (59), same collection data as holotype; D9516/T2015 (9), between Bhanga Neck and Kosi Bay , no. 13 reef, 6–18 m, living, dived D. Herbert et al., 12–20.vii.1987 ; E1005/T2212 (31), off Durban Bluff , 18–22 m, fine sand, leg. R. Kilburn and R. Fregona, 1983; S8687/T2213 (28), Aliwal Shoal, off Scottburgh, approx. 14 m, underwater pump, dived D. Herbert, 02.vi.1991 ; V1759 / T2214 (12), Stiebel Reef, north east of Phumula (30 o 37'S: 30 o 35'E), hand-dredged sand, ± 20 m, dived D. Herbert, 21.ii.1993 ; Eastern Cape: E255/T2016 (60), off Whale Rock (31 o 56.9'S: 29 o 13.5'E), 20–26 m, sand and gorgonians, dredged R.V. Meiring Naudé, 16.vii.1982 .

Additional material examined (selected samples, all NMSA): SOUTH AFRICA: northern KwaZulu-Natal: Leadsman Shoal, Reggie Reef, 8–12 m, a mixed algal and coral reef, 1–2 km, north of Leven Point , dived D. Herbert & NPB, 15.v.1988 (E7028) ; off St Lucia Lighthouse, 50 m, ex CSIR Water Research (A6172); Richards Bay , ex pisce, vi.1985 , don. J.P. Marais , vii.1985 (D1578) : central KwaZulu-Natal: off Durban Bluff, near Bluff caves, 10–15 m, dived D. Herbert, 07.v.1989 (E6544) ; between Umgababa and Umzimbazi River (30 o 08.6'S: 30 o 56.7'E), 70 m, fine sand, dredged R.V. Meiring Naudé, 08.vii.1986 (E6999) ; Aliwal

Shoal, off Umkomaas , 25–28 m, hand-dredged sand, dived D. Herbert, 16.xii.1990 (S9877) ; same data, (30.26690°S: 30.82302°E), 15.5 m, loose rubble, dived ORI, 07.xii.2004 (W2584, living) ; off Scottburgh , gravel reef, 26.vii.1987 (E405) ; Park Rynie , 50 m, coarse sand, 25.xi.1976 , ex CSIR Water Research, 1977 (B269); Lander’s Reef , off Park Rynie, 34 m, sand, dived D. Herbert, 02.vi.1991 (S6082) ; southern KwaZulu- Natal : “B.J.’s Reef”, off Hibberdene, 18–26 m, dived D. Herbert, 15.xi.1992 (V1845) ; off Phumula , 35 m, living on shell of Bolma andersoni (Smith, 1902) , dived M. Wallace, viii.1996 (V4004) ; same data, (30 o 38.279'S: 30 o 32.918'E), 36 m, on low profile reef, dived M. Wallace & V. Fraser, 07.xii.2004 (W2586, living) ; Glenmore Beach, south of Tongazi River mouth, intertidal rocks, leg. D. Herbert & M. Mander, 11.viii.1991 (S4123) . Eastern Cape (Transkei): off Mtamvuna River (31 o 09'9"S: 30 o 15'1"E), 140 m, sponge rubble, dredged R.V. Meiring Naudé, viii.1981 (C827) ; off Mzamba , from gut of slinger/stumpnose, leg. J.P. Marais, vii.1977 (A6650) ; Mzamba , beach-drift, leg. R. Kilburn & D. Herbert, 12–30.v.1986 (D2982) ; off Mtentu River (31 o 15'9''S: 30 o 05'0"E), 50 m, shell gravel, dredged R.V. Meiring Naudé, 12.viii.1981 (C1689) ; off Port Grosvenor (31 o 24.6'S: 29 o 57.2'E), 80 m, worn coral nodules, dredged R.V. Meiring Naudé, 16.viii.1981 (E179) ; same data, (29 o 57'6''S: 31 o 26'2''E), 100–115 m, sand, some mud, solitary coral, shells, dredged R.V. Meiring Naudé, viii.1981 (C1331) ; Port Grosvenor (31 o 23.9'S: 29 o 56.2'E), 60 m, sand, broken shell, dredged R.V. Meiring Naudé, viii.1981 (S3177) ; Mbotyi , beach-drift, leg. R. Kilburn & D. Herbert, v–vi.1985 (C8450) ; off Mbotyi (31 o 29'2''S: 29 o 45'4''E), 50 m, mixed sand, mud, abundant worm tubes, dredged R.V. Meiring Naudé, viii.1981 (C1750) ; off Whale Rock (31 o 56.9'S: 29 o 13.5'E), 20–26 m, sand and gorgonians, dredged R.V. Meiring Naudé, 16.vii.1982 (E6970, V4049) ; off Mncwasa Point (32 o 04.0'S: 29 o 05.7'E), 25– 30 m, fine sand, gorgonians, dredged R.V. Meiring Naudé, 19.vii.1982 (E341) ; off Qora River (32 o 33.6'S: 28 o 48.8'E), 300 m, coarse sand, some broken shell, dredged R.V. Meiring Naudé, 11.vii.1984 (S3166).

Taxonomic comparison: Specimens of T. adusta sp. n. were previously identified under the name T. africana (Bartsch 1915) . More thorough investigation, however, has revealed consistent differences in shell morphology. In comparison with T. adusta , T. africana is more elongate and has a higher spire, a proportionately smaller and more circular aperture, more convex whorls and frequently has light blue spots below the suture. In addition, the two species differ in terms of their habitat preferences: T. africana is an intertidal species, living on and under rocks in mid-shore pools, whereas T. adusta occurs amongst algal turf on subtidal reefs at depths of up to 70 m. In terms of shell shape T. adusta resembles T. formosa ( Turton 1932) , but lacks the pink spots on the apical whorls, characteristic of that species. All other species of Tricolia occurring in southern African differ markedly from T. adusta in terms of shell shape and/or sculpture.

Figures

Figs 1–8. Tricolia adusta sp. n., variation in shell colour and pattern: (1) holotype, length 3.30 mm, width 2.24 mm, NMSA E7143/T2013; (2–8) paratypes: (2) length 2.95 mm, width 1.89 mm, NMSA E1005/T2212, (3) length 3.89 mm, width 2.36 mm, NMSA E255/T2016, (4) length 3.30 mm, width 2.01 mm, NMSA E255/T2016, (5) length 3.78 mm, width 2.36 mm, NMSA V1759/T2214, (6) length 3.30 mm, width 2.24 mm, NMSA E255/T2016, (7) length 3.07 mm, width 2.12 mm, NMSA E1005/T2212, (8) length 3.54 mm, width 2.24 mm, NMSA S8687/T2213. [Available in colour at http://www.africaninvertebrates.org.za]

Fig. 15. Tricolia adusta sp. n., external anatomy: ct – cephalic tentacles; eso – epipodial sense organ; et – epipodial tentacle; lnl – left neck-lobe; rnl – right neck-lobe.

Fig. 16. Tricolia adusta sp. n., distribution map. Each black triangle represents one record.