Benthonellania hertzogi ( 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 : 349-351

Benthonellania hertzogi ( Thiele, 1925) n. comb.

( Figs 7 A-J; 9A, B; 13A; 26D; Table 1 )

Rissoa hertzogi Thiele, 1925: 82 , pl. 6, fig. 15.

TYPE MATERIAL. — Syntypes. South AFrica • 2 dd; Agulhas-Bank, Valdivia Stn 109; 35°19’S, 20°12’E; 126 m depth; ZMB /Moll. no. 64981 • 1 dd; Agulhas-Bank, Valdivia Stn 106; 35°26.8’S, 20°56.2’E; ZMB /Moll. no. 64981.

DISTRIBUTION AND SYMPATRY. — Benthonellania hertzogi n. comb. is known so far only from south of South Africa (Agulhas-Bank) ( Fig. 13A ).

DESCRIPTION [BASED ON THE TYPE MATERIAL]

Shell ( Figs 7 A-F; 9A)

Small for the genus, height 2.47-2.85 mm width 1.75-1.95 mm, height/width ratio 1.411 -1.461, rather solid, ovate-conical.

Protoconch ( Figs 7 I-J; 9B)

Dome-shaped, paucispiral, of 1.25 whorls, height 0.375 - 0.400 mm, nucleus diameter 0.200 - 0.212 mm, first half whorl diameter 0.350 -0.362 mm, maximum diameter 0.500 mm, glossy, smooth. Protoconch-teleoconch boundary distinct, slightly prosocline and marked by a slight thickening.

Teleoconch

Of 2.75-3.1 very slightly convex whorls, suture subcanaliculate, crowned by weak thinkening at tips of axial ribs, enhanced by a slight subsutural depression.Height last whorl 1.8-2.07 mm. height/height last whorl ratio 1.372 -1.377. Axial sculpture of 24-26 ribs on last whorl, slightly narrower than the interspaces, continuing partly on the base, prosocline, slightly curved on first whorls, markedly curved on last whorl. Spiral sculpture of 4-5 cordlets on last whorl, well spaced, slightly bulging at intersection with axial ribs, 1 above the aperture, 1 on the suture line and 2-3 on the base. Microsculpture of a very fine subsutural thread on first two teleoconch whorls ( Fig. 9B ) and weak growth striae on whole surface. Umbilical chink narrow. Aperture pyriform, height 1.25-1.4 mm, height/height aperture ratio 1.976 -2.036, peristome continuous, varix absent. Lip thin, orthocline or slightly prosocline, flexuose, smooth on the inside. Columella arcuate, simple.

Colour

Coloration of teleoconch and protoconch translucent white.

Operculum and soft parts

Unknown.

VARIABILITY

The variability of shell morphology is low in the few specimens examined (See Table 1 and Appendix 4).

REMARKS

The study of the type material showed that Rissoa hertzogi Thiele, 1925 ( Figs 7 A-J; 9A, B) and Rissoa africana Thiele, 1925 ( Figs 8 A-N; 9C, D) belong to this genus, with their paucispiral protoconchs devoid of spiral sculpture. Both species are very similar to e.g. B. agastachys , B. fayalensis and B. oligostigma with their slender shell and the crown of adapical thickening of axials, enhanced by the subsutural depression. We proposed thus, Benthonellania hertzogi ( Thiele, 1925) n. comb. and Benthonellania africana ( Thiele, 1925) n. comb. as new combinations for Rissoa hertzogi Thiele, 1925 and Rissoa africana Thiele, 1925 , respectively.

Benthonellania hertzogi n. comb. differs from B. basistriata n. sp. paucispiral vs multispiral protoconch, in its less canaliculated sutures, its tight umbilical chink, absent in B. basistriata , more numerous axial ribs (24-26 vs 14-20 in B. basistriata ).

See under Benthonellania africana n. comb. and B. thielei n. sp. for diagnostic comparison.

Figures

FIG. 7. — Benthonellania hertzogi (Thiele,1925),syntypes,Valdivia Stn 109 (ZMB–64981):A-C, syntype,height 2.85 mm (ZMB-64981);D-F, syntype,height 2.47 mm (ZMB-64981); G, original label; H, original drawings (Thiele 1925, 82, pl. 6, fig. 15, 16); I, J, syntype (A-C), detail of the first whorls. Scale bars: I, J: 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.

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.