Benthonellania africana ( Thiele, 1925 ) Amati & Giulio & Oliverio, 2022

Amati, Bruno, Giulio, Andrea Di & Oliverio, Marco, 2022, Deep-water Rissoidae of the genera Benthonella Dall, 1889 and Benthonellania Lozouet, 1990 (Gastropoda, Caenogastropoda, Rissooidea) from French Polynesia, Zoosystema 44 (12), pp. 335-389 : 351

Benthonellania africana ( Thiele, 1925) n. comb.

( Figs 8 A-N; 9C, D; 13A; 26G; Table 1 )

Rissoa africana Thiele, 1925: 83 , pl. 6, figs 20-22.

TYPE MATERIAL. — Lectotype. Somalia • dd (height 3.85 mm, width 2.15 mm, here designated, Figs 11 A-C; 13A, B); Valdivia Stn 251; 1°40.6’S, 41°47.1’E; ZMB/Moll. no. 64955a .

Paralectotypes • 223 dd (comprising 34 shells of Benthonellania africana n. comb. and 199 shells of Benthonellania thielei n. sp.); same locality data as lectotype; ZMB /Moll. no. 64955b.

There might be also material from Valdivia, Stn 245; 5°27.9’S, 39°18.8’E; 463 m depth ( Zanzibar) that we have not examined.

DISTRIBUTION AND SYMPATRY. — Benthonellania africana n. comb. is known from East Africa (off Somalia and possibly Zanzibar) 693 m depth. Benthonellania africana n. comb. is sympatric with Benthonellania thielei n. sp. at its type locality, off Somalia, and possibly with Benthonellania aequistriata at Zanzibar (fide Thiele) ( Fig. 13 ).

DESCRIPTION OF LECTOTYPE

Shell ( Figs 8 A-C; 9C, D)

Large for the genus, height 3.85 mm width 2.15 mm, height/ width ratio 1.790, rather solid, ovate-conical.

Protoconch ( Figs 8J, K ; 9D )

Dome-shaped, paucispiral,of 1.4 whorls, height 0.375 mm, nucleus diameter 0.200 mm, first half whorl diameter 0.362 mm, maximum diameter 0.525 mm, glossy, smooth, except for a faint and confused spiral sculpture on the nucleus ( Fig. 9D ). Protoconch-teleoconch boundary barely visible.

Teleoconch

Of 4.1 very slightly convex whorls, suture canaliculate, crowned by small tubercles at tips of axial ribs, highlighted by a slight subsutural depression. Height last whorl 2.50 mm, height/ height last whorl ratio 1.540. Axial sculpture of 9 ribs on last whorl, as broad as the interspaces, prosocline and slightly curved, curvature more pronounced on last whorl, gradually vanishing at the base; last half whorl progressively devoid of axial sculpture. Spiral sculpture of 4 very weak cordlets on last whorl above the aperture and on the suture line, the uppermost suprasutural visible on all whorls, base smooth ( Fig. 8N ). Microsculpture of only growth striae. Umbilical chink conspicuous. Aperture pyriform, large, height 1.55 mm, height/height aperture ratio 2.483, peristome continuous, varix absent. Thin lip with prosocline inclination. Columella arcuate, simple.

Colour

Coloration of teleoconch and protoconch translucent, white.

Operculum

Thin, light yellow with an eccentric nucleus.

Soft parts

Unknown.

VARIABILITY Species not very variable (See Table 1 and Appendix 5). It reaches 4 mm in height and 2.35 mm in width; height/width ratio 1.574 -1.860; number of axial ribs on the last whorl: 8-10. Maximum diameter of the protoconch 0.575 mm.

REMARKS

Rissoa africana Thiele, 1925 is currently classified in Haurakia based on Ponder (1985: 30). Ponder (1985) also considered Rissoa africana and R. aequatorialis as synonyms (selecting Pusillina (Haurakia) africana as senior one, as first reviser).This is clearly a member of Benthonellania , with its shell with canaliculate suture, crowned by small tubercles at the tips of axial ribs, enhanced by a slight subsutural depression. We accordingly propose Benthonellania africana ( Thiele, 1925) n. comb. as a new combination for Rissoa africana Thiele, 1925 . Cithna africana Bartsch, 1915 (taxon inquirendum: MolluscaBase 2021e) from South Africa, has a small shell (height 0.7 mm, width 0.7 mm), devoid of sculpture, and cannot be classified either in Benthonella or in Benthonellania (see Bartsch 1915: 120, pl. 21, fig. 5).

The examined type material of Rissoa africana , comprises two distinct species: one (corresponding to Thiele 1925: fig. 20) has a rather thick shell, more or less slender profile, spiral sculpture of 3-4 very weak cordlets on the last whorl above the aperture and on the suture line and a crown of small tubercles at tip of axial ribs, paucispiral protoconch smooth, except for a faint and confused spiral sculpture on the nucleus; 199 shells (corresponding to Thiele 1925: figs 21, 22) belong to a distinct species that we describe below as B. thielei n. sp. To stabilize the use of the name, the lectotype of Rissoa africana Thiele, 1925 is herein designated on a specimen of the first form.

Benthonellania africana n. comb. differs from B. hertzogi n. comb. by its higher height/width ratio (1.574 -1.860 vs 1.250 -1.400 in B. hertzogi n. comb.), the lower axial ribs in B. hertzogi n. comb. and the presence of a very fine subsutural thread on first two teleoconch whorls in B. hertzogi n. comb., absent in B. africana n. comb.

See under, Benthonellania thielei n. sp., Benthonellania aequatorialis n. comb. and Benthonellania alis n. sp. for diagnostic comparison.

Figures

FIG. 8. — Benthonellania africana (Thiele,1925) n. comb.: A-C, lectotype, height 3.85 mm; D-F, paralectotype height 3.7 mm; G-I, paralectotype,height 3.35 mm; Valdivia Stn 251, ZMB–64955; J, K, paralectotype, detail of the first whorls; L, original label; M, original drawing (Thiele 1925, 83, pl. 6, fig. 20); N, paralectotype, detail of the teleoconch sculpture spiral on the last whorl. Valdivia Stn 251, ZMB–64955. Scale bars: J, K, N, 0.50 mm.

FIG. 11. — Benthonellania aequatorialis (Thiele, 1925) n. comb., syntypes: A-C, height 1.8 mm; D, height 1.95 mm; E, original label; F, original drawing (Thiele 1925, 84, pl. 6, fig. 23); G, syntype, detail of the first whorls; Valdivia Stn 199, ZMB-64973. Scale bar: G, 0.25 mm.

FIG. 13. — Maps of the known distribution of: A, Benthonellania hertzogi (◯), and Benthonellania thielei n. sp. and Benthonellania africana (Thiele, 1925) n. comb. (both); B, Benthonellania aequatorialis (Thiele, 1925) n. comb.

FIG. 9. — Benthonellania spp. (SEM): A, B, Benthonellania hertzogi (Thiele, 1925), syntype, Agulhas-Bank (south of South Africa), height 2.85 mm, ZMB/Moll. no. 64981, shell (A), detail of the protoconch (B); C, D, Benthonella africana (Thiele, 1925) n. comb., lectotype, East Africa (off Somalia), height 3.85 mm, ZMB/ Moll. No. 64955a, shell (C), detail of the protoconch (D). Scale bars: B, D, 100 μm.