Benthonella basistriata, 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 : 343-344

Benthonella basistriata n. sp.

( Figs 3 A-H; 5F, G; 25B; 26B; Tables 1 ; 2)

urn:lsid:zoobank.org:act:98730F8F-ECFB-479D-BE22-82E2DB64DF15

TYPE MATERIAL. — Holotype. Tuamotu . • dd (height 2.0 mm, width 1.3 mm, Figs 8 A-D; 10F, G); Tikehau , TARASOC Stn DW3389 ; 14°55’S, 148°15’W; 889 m depth; MNHN-IM-2000-37668 .

Paratypes • 2 dd; same locality data as holotype; MNHN- IM-2000-37669.

TYPE LOCALITY. — Tuamotu, Tikehau, TARASOC Stn DW3389, 14°55’S, 148°15’W, 889 m depth.

OTHER MATERIAL EXAMINED. — Society Islands • 1 dd; Huahine, TARASOC Stn DW 3425; 16°43’S, 151°03’W; 557 m; 14.X.2009; MNHN • 2 dd; Huahine, TARASOC Stn DW 3435; 16°41’S, 151°02’W; 500-612 m; 15.X.2009; MNHN • 1 dd; Moorea, TARASOC Stn DW3459; 17°28’S, 149°48’W; 485-560 m; 19.X.2009 • 3 dd; Moorea, TARASOC Stn DW3481; 17°29’S, 149°45’W; 610 m; 22.X.2009 • 1 dd; Moorea, TARASOC Stn DW 3474; 17°28’S, 149°50’W; 720 m; 21.X.2009; MNHN.

Tuamotu • 15 dd; Kaukura, TARASOC Stn DW 3373; 15°41’S, 146°54’W; 507-607 m; 4.X.2009; MNHN .

DISTRIBUTION AND SYMPATRY. — The species is known from the South Pacific Ocean in the Tuamotu (Tikehau, Kaukura) and Society Islands (Huahine, Moorea), with empty shells collected in 485-889 m depth ( Fig. 25B ).

Benthonella basistriata n. sp. is sympatric with Benthonella communis n. sp. at the Society Islands (Huahine, Moorea), Tuamotu (Kaukura); with Benthonellania bouteti n. sp. at the Tuamotu (Kaukura, Tikehau), Society Islands (Huahine, Moorea); with Benthonellania tarava n. sp. at the Tuamotu (Kaukura, Tikehau), Society Islands (Moorea); with Benthonellania tuamotu n. sp. at the Tuamotu (Kaukura, Tikehau) ( Table 2).

ETYMOLOGY. — For the particularly marked basal sculpture, from the Latin basis – base, striata – striated.

DESCRIPTION OF HOLOTYPE

Shell ( Figs 3 A-D; 5F, G)

Small for the genus, height 2.0 mm, width 1.3 mm, height/ width ratio 1.538, rather solid, ovate-conical.

Protoconch ( Figs 3D ; 5G )

Multispiral,dome-shaped, of2.5 whorls, height 0.3375mm, nucleus diameter 0.075 mm, first half whorl diameter 0.125 mm, maximum diameter 0.375 mm; protoconch I with 5 spiral threads, interspaces covered by microtubercles ( Fig. 5G ); protoconch II with 2 fine spiral cordlets, with irregularly set microtubercles on the subsutural area ( Fig. 5G ). Protoconchteleoconch boundary indistinct.

Teleoconch

Of 3.25 whorls, the first 2 flat, the others slightly convex, sutures canaliculate, crowned by small tubercles on tip of axial ribs. Height last whorl 1.3 mm, height/height last whorl ratio 1.538. Axial sculpture on the last whorl of 18 curved, opisthocline ribs, almost as broad as the interspaces, gradually vanishing on the base. Spiral sculpture of 6 weak, fine cordlets, only on the base of last whorl (abapical last barely visible); one suprasutural cordlet visible on upper whorls. Microsculpture of only growth striae. Umbilical chink absent. Aperture pyriform, small, height 0.8 mm. height/height aperture ratio 2.424, peristome continuous, varix large; outer lip (broken) prosocline, internally smooth, sharp. Columella angled, simple.

Colour

Coloration of teleoconch white, outer lip orange faded, darker than subsutural zone, protoconch whitish-orange.

Operculum and soft parts

Unknown.

VARIABILITY

Species not very variable (See Table 1 and Appendix 2). Maximum height 2.60 mm, width 1.65 mm (from Tuamotu: Tikehau 889 m). The number of axial ribs on the last whorl can vary from 14 to 20.

REMARKS

Benthonella basistriata n. sp. is similar in the general shape to the fossil Benthonella lutetiana Lozouet, 2014 and Benthonella priabonica Lozouet, 2014 , both from the Eocene of France (see Lozouet 2014: 24-25, 28; 2I-K; 5A-E and 2014: 24-25, 29, figs 2L-N; 6A-H, respectively). They are essentially distinguished by the different sculpture of the protoconch II: B. lutetiana and B. priabonica have two thin spiral cordlets, one abapical close to the suture, the other adapical closer to the suture in B. lutetiana ; B. basistriata n. sp. has two broader spiral cordlets, the adapical farther from the suture, and microgranules on the subsutural area (apparently lacking in the fossil species).

Benthonella olangoensis ( Poppe,Tagaro & Stahlschmidt, 2015) has a similar outline. It differs in the fewer spiral cordlets (2-3 vs 5-6 in B. basistriata n. sp.: based on the photos of the type material, since in the original description, this sculpture and the precise number of cordlets are not reported).

B. basistriata n. sp. also resembles Benthonellania agastachys Bouchet & Warén, 1993 . Benthonella basistriata n. sp. has a spiral sculpture of 6 basal cords vs c. 10 basal cords in an adult specimen of Benthonellania agastachys figured by Ortega & Gofas (2019: 525, figs 8 A-D; the holotype with 4-5 cords is a juvenile); the umbilical chink absent vs present in B. agastachys ; the protoconch multispiral, with two fine spiral cordlets and subsutural microtubercles vs paucispiral, lacking spiral cordlets, densely granulated, with granules tending to be spirally arranged in B. agastachys (see Bouchet & Warén 1993: 682, figs 1584, 1592-1593).

See under Benthonellania hertzogi ( Thiele, 1925) n. comb. and Benthonellania thielei n. sp. for deatailed comparisons.

Figures

FIG. 3. — Benthonella basistriata n. sp.: A-D, holotype, height 2.0 mm, width 1.3 mm, Tuamotu: TARASOC Stn DW3389 889 m 14°55’S, 148°15’W (MNHN- IM-2000-37668); E-G, specimen, height 2.25 mm, width 1.5 mm, Society Islands: TARASOC Stn DW3481, 610 m, 17°29’S, 149°45’W; H, specimen, height 2.52 mm, width 1.55 mm, Society Islands: TARASOC Stn DW3435 500-612 m, 16°41’S, 151°02’W, MNHN. Scale bar: D, 0.50 mm.

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. 25. — Distribution maps of the Polynesian species of Benthonella Dall,1889 and Benthonellania Lozouet,1990: A, Benthonella boucheti n. sp.;B, Benthonella basistriata n. sp.; C, Benthonella communis n. sp.; D, Benthonellania bouteti n. sp.; E, Benthonellania alis n. sp.; F, Benthonellania tarava n. sp. (◯) and Benthonellania lozoueti n. sp. (); G, Benthonellania megan n. sp. (◯) and Benthonellania maestratii n. sp. (); H, Benthonellania tuamotu n. sp.

FIG. 5. — Benthonella spp. (SEM): A-E, Benthonella boucheti n. sp. holotype, MNHN-IM-2000-37666, Tarava Seamounts, height 4.32 mm: A, shell; B, C, detail of the protoconch microsculture; D, detail of the teleoconch sculpture spiral; E, detail of the first whorls; F, G, Benthonella basistriata n. sp. holotype, MNHN- IM-2000-37668, Tuamotu,height 2.0 mm:F, shell; G, detail of the protoconch microsculture;H-J, Benthonella communis n. sp., holotype,MNHN-IM-2000-37670, Tarava Seamounts: height 2.2 mm; H, shell; I, J, detail of the protoconch microsculture. Scale bars: B, 40 μm; C, J, 20 μm; D, E, I, 100 μm; G, 50 μm.