Benthonellania tarava, 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 : 364-365

Benthonellania tarava n. sp.

( Figs 17 A-K; 19A-E; 25F; 26K; Tables 1 ; 2)

urn:lsid:zoobank.org:act:DCA27C86-C251-4615-B4D9-811FA5EAF87A

TYPE MATERIAL. — Holotype. Tarava Seamounts • 1 dd (height 3.5 mm, width 1.85 mm, Figs 17 I-K; 19A-E); Mont ‘Otaha , TARASOC Stn DW3333 ; 18°45’S, 152°18’W; 26.IX.2009; 795-975 m depth; MNHN-IM-2000-37687 .

Paratypes. Tarava Seamounts • 30 dd; same locality data as holotype; MNHN-IM-2000-37688 • 3 dd; Mont ‘Otaha, Stn DW3331; 18°45’S, 152°17’W; 26.IX.2009; 766 m depth; MNHN-IM-2000-37689 • 29 dd; Mont ‘Otaha, Stn DW3328; 18°46’S, 152°15’W; 26.IX.2009; 788-836 m depth; MNHN-IM-2000-37690 • 46 sh; Mont ‘Otaha, Stn DW3327; 747- 18°45’S, 152°16’W; 26.IX.2009; 836 m dept; MNHN-IM-2000-37691 • 3 dd; Mont ‘Otaha, Stn CP3329; 18°45’S, 152°16’W; 26.IX.2009; 755-840 m depth; MNHN-IM-2000-37692 • 10 dd; Mont ‘Otaha, Stn DW3332; 18°45’S, 152°18’W; 26.IX.2009; 790-880 m depth; MNHN-IM-2000-37693 • 2 dd; Mont ‘Otaha, Stn DW3330; 18°45’S, 152°16’W; 26.IX.2009; 717-794 m depth; MNHN-IM-2000-37694.

TYPE LOCALITY. — Tarava Seamounts, Mont ‘Otaha, TARASOC Stn DW3333; 18°45’S, 152°18’W; 795-975 m depth.

OTHER MATERIAL EXAMINED. — Society Islands • 1 dd, 1 lv; Moorea, TARASOC Stn DW 3461; 17°27’S, 149°49’W; 19.X.2009; 844- 877 m depth; MNHN .

Australes • 1 dd; Rimatara, BENTHAUS Stn DW 2020; 22°37’S, 152°49’W; 25.XI.2002; 920-930 m depth; MNHN • 51 dd; South coast of Rurutu, BENTHAUS Stn DW 2010; 22°32’S, 151°21’W 24.XI.2002; 520-950 m depth; MNHN • 2 dd; East coast of Rurutu, BENTHAUS Stn 2004; 22°28’S, 151°19’W; 24.XI.2002; 430-850 m depth; MNHN .

Tuamotu • 13 dd; SW Kaukura, TARASOC Stn DW3359; 15°57’S, 147°08’W; 1.X.2009; 462-980 m depth; MNHN • 1 dd; Kaukura , TARASOC Stn DW 3379; 15°38’S, 146°51’W; 5.X.2009; 800 m depth; MNHN • 1 dd; Kaukura , TARASOC Stn DW 3380; 15°39’S, 146°56’W; 5.X.2009; 970-1060 m depth; MNHN • 154 dd; between Tikehau and Rangiroa, TARASOC Stn DW 3349; 15°05’S, 148°03’W; 30.IX.2009; 976-997 m depth; MNHN • 6 dd; between Tikehau and Rangiroa, TARASOC Stn DW 3351; 15°04’S, 148°01’W; 30.IX.2009; 976-983 m depth; MNHN • 4 dd; Tikehau ,TARASOC Stn DW 3389; 14°55’S, 148°15’W; 6.X.2009; 889 m depth; MNHN. Tarava Seamounts • 10 dd; Mont Honu , TARASOC Stn DW 3340; 18°24’S, 154°09’W; 27.IX.2009; 787-792 m depth; MNHN • 3 dd; Mont Ari’i Moana , TARASOC Stn DW 3314; 19°14’S, 151°39’W; 24.IX.2009; 803-815 m depth; MNHN .

DISTRIBUTION AND SYMPATRY. — The species is at present known from the South Pacific Ocean, at Tarava Seamounts (Mont Ari’i Moana, Mont ‘Otaha, Mont Honu), Society Islands (Moorea), Tuamotu (SW Kaukura, Kaukura, between Tikehau and Rangiroa, Tikehau,) and Australes (Rimatara, South coast of Rurutu, East coast of Rurutu), with empty shells collected in 430-1250 m depth, and a single live collected specimen, from the Society Islands (Moorea), 844-877 m depth 17°27’S, 149°49’W ( Fig. 25F ).

Benthonellania tarava n. sp. is sympatric with Benthonella boucheti n. sp. at the Tarava Seamounts (Mont Honu and Mont ‘Otaha), Australes (Rimatara, South coast of Rurutu, East coast of Rurutu); with Benthonella basistriata n. sp. at theTuamotu (Tikehau, Kaukura), Society Islands (Moorea); with Benthonellania maestratii n. sp. at the Australes (South coast of Rurutu); with Benthonella communis n. sp. at the Tarava Seamounts (Mont Ari’i Moana), Society Islands (Moorea), Tuamotu (SW Kaukura, Kaukura, between Tikehau and Rangiroa), Australes (Rimatara, South coast of Rurutu, East coast of Rurutu); with Benthonellania bouteti n. sp. at the Tarava Seamounts (Mont Ari’i Moana, Mont ‘Otaha, Mont Honu), Society Islands (Moorea), Tuamotu (SW Kaukura, Kaukura, Tikehau, between Tikehau and Rangiroa), Australes (Rimatara, South coast of Rurutu, East coast of Rurutu); with Benthonellania tuamotu 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 megan n. sp. at the Australes (Rimatara); with Benthonellania alis n. sp. at the Tarava Seamounts (Mont ‘Otaha, Mont Honu), Australes (Rimatara, South coast of Rurutu, East coast of Rurutu) ( Table 2).

ETYMOLOGY. — The name is after the area of the type locality, the Tarava Seamounts, used as a noun in apposition.

DESCRIPTION OF HOLOTYPE

Shell ( Figs 17 I-K; 19A-E)

Medium for the genus, height 3.5 mm, width 1.85 mm, height/ width ratio 1.891, not very solid, ovate-conical, rather slender.

Protoconch ( Fig. 19 B-D)

Multispiral, of 2.75 whorls, height 0.425 mm, nucleus diameter 0.0625 mm, first half whorl diameter 0.200 mm, maximum diameter 0.4625 mm; protoconch I seemingly with only microtubercles spirally arranged (embryonic shell in poor condition) ( Fig. 19C ), protoconch II with two fine spiral cordlets, interspaced by a large smooth median area ( Fig. 19B, D ). Protoconch-teleoconch boundary marked, opisthocline, sinuous.

Teleoconch

Of c. 3.45 slightly convex whorls, suture canaliculate, crowned by small tubercles at tip of axial ribs, highlighted by a subsutural spiral groove. Height of last whorl 2.1 mm, height/ height last whorl ratio 1.666. Axial sculpture of 9 flexuose, acute and opisthocline ribs on last whorl, almost orthocline on first whorls, narrower than interspaces, abruptly interrupted before the base. Last half whorl progressively devoid of axial ribs. Spiral sculpture of 3 fine cordlets visible only on the base on last whorl, the third upper cordlets is also visible on the upper whorls. Microsculpture of only growth striae ( Fig. 19E ). Umbilical chink present. Aperture pyriform, small, height 1.27 mm, height/height aperture ratio 2.745, peristome continuous, varix absent; outer lip slightly opisthocline, internally smooth (broken). Columella arcuate, simple.

Colour

Coloration of teleoconch white, protoconch orange.

Operculum and soft parts

Unknown.

VARIABILITY

Species not very variable (See Table 1 and Appendix 10). Generally, on the last quarter of a whorl, the axial ribs flatten and the subsutural nodules become smaller. A probably teratological subadult specimen from Mont ‘Otaha (Tarava Seamounts: TARASOC Stn DW3327 747-836 m 18°45’S, 152°16’W), showed an obsolete axial sculpture, absent on the last whorl. The spiral cordlets (2-3) are almost imperceptible, making a correct count possible only under raking light. Rare specimens (from South coast of Rurutu, 520-950 m) have up to four very weak spiral cordlets on the base.

REMARKS

Benthonellania tarava n. sp. is similar to Benthonellania gofasi Lozouet, 1990 , Benthonellania acuticostata ( Dall, 1889) and Benthonellania xanthias (R. B. Watson, 1886) , all species with slender shells, which however differ in their more numerous spiral cordlets on the last whorl, and for the different sculptures of the respective protoconchs: with 4 irregular spiral cords; with a series of very jagged spiral cordlets intersecting each other to form a cobweb; with 2 spiral cordlets with short vertical pustules on the lower half of the whorls vs with two fine spiral cordlets, interspaced by a large smooth median area in B. tarava n. sp. (see ( Lozouet 1990: 322, fig. 23; Dall 1889: 280, pl. XIX, fig. 10; R. B. Watson 1886: 588, pl. XLIV, fig. 5).

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

Figures

FIG. 17. — Benthonellania tarava n. sp.:A-C, paratype,height 3.6 mm, width 1.85 mm, Tarava Seamounts:TARASOC Stn DW3333,795-975 m, 18°45’S,152°18’W, MNHN-IM-2000-37688; D-H, paratype, height 3.75 mm, width 1.92 mm, Tarava Seamounts: TARASOC Stn DW3333, 795-975 m, 18°45’S, 152°18’W, MNHN- IM-2000-37688; I-K, holotype,height 3.5 mm,width 1.85 mm,Tarava Seamounts:TARASOC Stn DW3333,795-975 m, 18°45’S,152°18’W, MNHN-IM-2000-37687. 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. 19. — Benthonellania spp. (SEM): A-E, Benthonellania tarava n. sp., holotype, Tarava Seamounts, height 3.5 mm, MNHN-IM-2000-37687: shell (A); detail of the protoconch microsculture (B-D); detail of the teleoconch axial sculture (E); F-H, Benthonellania megan n. sp., holotype, Marquesas, height 2.7 mm, MNHN- IM-2000-37695: shell (F); detail of the protoconch microsculture (G, H). Scale bars: B, E, G, H, 100 μm; C, 20 μm; D, 50 μm.