Benthonellania tuamotu, 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 : 368-370

Benthonellania tuamotu n. sp.

( Figs 20 A-K; 22A-D; 25H; 26M; Tables 1 ; 2)

urn:lsid:zoobank.org:act:49FA642C-D59A-49E5-9B73-0A544D048F6A

TYPE MATERIAL. — Holotype. Tuamotu • 1 dd (height 4.42 mm, width 2.5 mm, Figs 20 A-C; 22A-D); Tikehau , TARASOC Stn DW 3388; 14°56’S, 148°14’W; 6.X.2009; 820-835 m depth; MNHN- IM-2000-37697.

Paratypes • 3 dd; same locality data as holotype • 2 dd; MNHN- IM-2000-37699; Tikehau , Stn DW 3389; 14°55’S, 148°15’W; 6.X.2009; 889 m depth; MNHN-IM-2000-37698 • 1 dd; Tikehau , Stn DW 3387; 14°57’S, 148°16’W; 6.X.2009; 550-600 m depth; MNHN-IM-2000-37700 .

TYPE LOCALITY. — Tuamotu, Tikehau, TARASOC Stn DW3388; 14°56’S, 148°14’W; 820-835 m depth.

OTHER MATERIAL EXAMINED. — Tuamotu • 3 dd; SW Kaukura, TARASOC Stn DW3359; 15°57’S, 147°08’W; 1.X.2009; 462-980 m depth; MNHN • 5 dd, 1 lv; Kaukura, TARASOC Stn DW 3373; 15°41’S, 146°54’W; 4.X.2009; 507-607 m depth; MNHN • 8 dd; between Tikehau and Rangiroa, TARASOC Stn DW 3349; 15°05’S, 148°03’W; 30.IX.2009; 976-997 m depth; MNHN .

Society Islands • 1 dd; Maupiti, TARASOC Stn DW 3407; 16°32’S, 152°31’W; 12.X.2009; 445-645 m depth; MNHN • 1 dd; Raiatea, TARASOC Stn DW 3451; 16°53’S, 151°21’W; 18.X.2009; 440- 490 m depth; MNHN .

Tarava Seamounts • 1 dd; Mont Punu Taipu, TARASOC Stn DW 3308; 19°16’S, 151°01’W; 23.IX.2009; 592-632 m depth; MNHN • 1 dd; Mont ‘ Otaha, TARASOC Stn DW 3327; 18°45’S, 152°16’W; 26.IX.2009; 747-836 m depth; MNHN • 2 dd; Mont ‘ Otaha, TARASOC Stn DW 3333; 18°45’S, 152°18’W; 26.IX.2009; 795-975 m depth; MNHN .

Australes • 1 dd; Rimatara, BENTHAUS Stn DW 2021; 22°37’S, 152°49W; 25.XI.2002; 1200-1226 m depth; MNHN • 2 dd; Rimatara, BENTHAUS Stn DW 2020; 22°37’S, 152°49’W; 25.XI.2002; 920- 930 m depth; MNHN • 3 dd; South coast of Rurutu, BENTHAUS Stn DW 2010; 22°32’S, 151°21’W; 25.XI.2002; 520-950 m depth; MNHN • 1 dd; Récif Neilson, BENTHAUS Stn DW 1925; 27°00’S, 146°05’W; 12.XI.2002; 560-790 m depth; MNHN .

DISTRIBUTION AND SYMPATRY. — The species is at present known from the South Pacific Ocean, at Tarava Seamounts (Mont ‘Otaha, Mont Punu Taipu), Society Islands (Maupiti, Raiatea), Tuamotu (SW Kaukura, between Tikehau and Rangiroa, Tikehau, Kaukura) and Australes (Rimatara, South coast of Rurutu, Récif Neilson), with empty shells collected in 440-997 m depth, and a single live collected specimen, from Tuamotu, Kaukura,TARASOC Stn DW3373 507-607 m 15°41’S, 146°54’W ( Fig. 25H ).

Benthonellania tuamotu n. sp. is sympatric with Benthonella boucheti n. sp. at the Tarava Seamounts (Mont ‘Otaha), Australes (Rimatara, South coast of Rurutu, Récif Neilson); with Benthonella basistriata n. sp. at the Tuamotu (Tikehau, Kaukura); with Benthonellania maestratii n. sp. at the Australes (Récif Neilson, South coast of Rurutu); with Benthonella communis n. sp. at the Tarava Seamounts (Mont Punu Taipu), Society Islands (Maupiti, Raiatea), Tuamotu (WS Kaukura, Kaukura between Tikehau and Rangiroa, Tikeha), Australes (Rimatara, South coast of Rurutu, Récif Neilson); with Benthonellania bouteti n. sp. at the Tarava Seamounts (Mont ‘Otaha, Mont Punu Taipu), Tuamotu (SW Kaukura, Kaukura, between Tikehau and Rangiroa, Tikehau), Society Islands (Maupiti, Raiatea), Australes (Rimatara, South coast of Rurutu, Récif Neilson); with Benthonellania tarava n. sp. at the Tarava Seamounts (Mont ‘Otaha), Tuamotu (SW Kaukura, Kaukura, between Tikehau and Rangiroa, Tikehau), Australes (Rimatara, South coast of Rurutu); with Benthonellania alis n. sp. at the Tarava Seamounts (Mont ‘Otaha, Mont Punu Taipu), Australes (Rimatara, South coast of Rurutu) ( Table 2).

ETYMOLOGY. — After the name of the area of the type locality (Tuamotu Islands), used as a noun in apposition.

DESCRIPTION OF HOLOTYPE

Shell ( Figs 20 ; 22 A-D)

Large for the genus, height 4.42 mm, width 2.5 mm. height/width ratio 1.77, not very solid, ovate-conical, rather slender, with slightly stepped outline, broad base and large aperture.

Protoconch ( Fig. 22B, D )

Multispiral, acute of 2.30 whorls, height 0.40 mm, nucleus diameter 0.10 mm, first half whorl diameter 0.187 mm, maximum diameter 0.475 mm; (protoconch I in poor condition) protoconch II with two spiral cordlets with a wavy-zigzag pattern in the upper area, two fine spiral keels in the lower half; in the interspaces oblique microstructures ( Fig. 22B ). Protoconch-teleoconch boundary marked, prosocline, sinuous.

Teleoconch

Of 4.5 whorls, almost flat adapically, the last ones convex, suture canaliculate, crowned by large tubercles at tips of axial ribs, highlighted by a subsutural spiral groove. Height last whorl 2.9 mm, height/height last whorl ratio 1.524. Axial sculpture of 20 slightly curved, barely acute and prosocline ribs on last whorl, almost orthocline on first whorls, slightly narrower than interspaces, abruptly interrupted before the base. Spiral sculpture of 4 fine cordlets only on the base on last whorl. Microsculpture only growth striae ( Fig. 22C ). Umbilical chink absent. Aperture pyriform, small, height 1.85 mm, height/height aperture ratio 2.391, peristome continuous, outer lip (broken) internally smooth. Columella arcuate, slightly angular, simple.

Colour

Coloration of teleoconch translucent white, protoconch orange.

Operculum and soft parts

Unknown.

VARIABILITY

Species not very variable (See Table 1 and Appendix 12). The only adult specimen (Tuamotu, Kaukura 507-607 m depth) with soft parts and operculum inside the shell, has the intact outer lip without varix.

REMARKS

Benthonellania charope ( Melvill & Standen, 1901) from the Gulf of Oman (c. 374 m depth), and Benthonellania profundior ( Hedley, 1907) n. comb. from 33 miles east of Sydney (c. 1458 m depth), are very similar to each other, and to Benthonella tuamotu n. sp. for their outline with stepped whorls. However, both have paucispiral vs multispiral protoconch in B. tuamotu n. sp., are smaller (height 1.75 mm B. charope and 2.95 mm B. profundior n. comb. mm vs 3.60-4.95 mm in B. tuamotu n. sp.), have lower height/width ratios (1.476 -1.596 in B. charope and 1.478 -1.609 in B. profundior vs 1.625 -1.787 in B. tuamotu n. sp.) and more pronounced spiral sculptures (see Melvill & Standen 1901: 365, pl. XXII, fig. 8; Hedley 1907: 358, pl. LXVII, fig. 15).

See under Benthonellania lozoueti n. sp. for diagnostic comparison.

Figures

FIG. 20. — Benthonellania tuamotu n. sp.: A-C, holotype, height 4.42 mm, width 2.5 mm, Tuamotu, TARASOC Stn DW3388, 820-835 m, 14°56’S, 148°14’W, MNHN-IM-2000-37697, D-H, paratype, height 3.4 mm, width 1.95 mm, type locality, MNHN-IM-2000-37698; I-K, specimen, height 4.70 mm, width 2.75 mm, Tuamotu: TARASOC Stn DW3349, 976-997 m, 15°06’S, 148°03’W. Scale bars: G, H, 0.25 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. 22. — Benthonellania spp. (SEM): A-D, Benthonellania tuamotu n. sp., holotype, MNHN-IM-2000-37697, Tuamotu: height 4.42 mm: shell (A), detail of the protoconch microsculture (B, D); detail of the teleoconch axial sculture (C); E-I, Benthonellania lozoueti n. sp., holotype, MNHN-IM-2000-3770, Marquesas:height 3.86 mm:shell (E), detail of the protoconch microsculture (F-H), detail of the teleoconch axial sculture (I). Scale bars:B, H, 50 μm;C, D, I, 100 μm;F,30 μm;G,20 μm.