Benthonellania megan, 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 : 366-368

Benthonellania megan n. sp.

( Figs 18 A-K; 19F-H; 25G; 26L; Tables 1 ; 2)

urn:lsid:zoobank.org:act:9B36A331-6E3D-48ED-8B90-31C7D64BB919

TYPE MATERIAL. — Holotype. Marquesas • 1 dd (height 2.7 mm, width 1.6 mm, Figs 18 A-E; 19F-H); Fatu Hiva , MUSORSTOM 9 Stn DR1247 ; 10°34’S, 138°42’W; 1.IX.1997; 1150-1250 m depth; MNHN-IM-2000-37695 .

Paratypes. Marquesas • 5 dd; same locality data as holotype; MNHN-IM-2000-37696 .

TYPE LOCALITY. — Marquesas, Fatu Hiva, MUSORSTOM 9 Stn DR1247; 10°34’S, 138°42’W; 1150-1250 m depth.

OTHER MATERIAL EXAMINED. — Australes • 1 dd; Rimatara, BENTHAUS Stn DW2021; 22°37’S, 152°49’W; 25.XI.2002; 1200-1226 m depth.

DISTRIBUTION AND SYMPATRY. — The species is at present known from the South Pacific Ocean, at Marquesas (Fatu Hiva Island) and Australes (Rimatara), with only empty shells collected in 1150- 1250 m depth ( Fig. 25G ).

Benthonellania megan n. sp. is sympatric with Benthonella boucheti n. sp. at the Marquesas (Fatu Hiva Island) and Australes (Rimatara); with Benthonella communis n. sp. at the Australes (Rimatara); with Benthonellania bouteti n. sp. at the Australes (Rimatara); with Benthonellania tarava n. sp. at the Australes (Rimatara); with Benthonellania lozoueti n. sp. at the Marquesas (Fatu Hiva Island); with Benthonellania alis n. sp. at the Australes (Rimatara) ( Table 2).

ETYMOLOGY. — Dedicated to Megan Zampa, granddaughter of one of the authors (B. Amati).

DESCRIPTION OF HOLOTYPE

Shell ( Figs 18 A-C; 19F-H)

Small for the genus, height 2.7 mm, width 1.6 mm, height/ width ratio 1.687, pretty solid, ovate-conical.

Protoconch ( Figs 18D, E ; 19G, H )

Multispiral, acute of 2.5 whorls, height 0.40 mm, nucleus diameter 0.095 mm, first half whorl diameter 0.162 mm, maximum diameter 0.437 mm; (protoconch I in poor condition), protoconch II with two fine spiral keels, the lower larger, a fine cordlet of microtubercles in the subsutural area. Microtubercles spread over the entire surface ( Fig. 19G, H ). Protoconch-teleoconch boundary barely visible, sinuous.

Teleoconch

Of c. 3.5 convex whorls, suture canaliculate, crowned by small tubercles at tips of axial ribs. Height last whorl 1.75 mm, height/height last whorl ratio 1.542. Axial sculpture of 16 curved, slightly opisthocline ribs on last whorl, slightly narrower than interspaces, abruptly interrupted on the suture line. Spiral sculpture of 3 very weak fine cordlets on the base. Microsculpture of only growth striae ( Fig. 19H ). Umbilical chink absent. Aperture pyriform, large, height 1.1 mm, height/height aperture ratio 2.454, peristome continuous, varix absent (outer lip broken). Columella arcuate, simple.

Colour

Coloration of teleoconch translucent white, protoconch orange.

Operculum and soft parts

Unknown.

VARIABILITY

Species not very variable (See Table 1 and Appendix 11).

REMARKS

All the examined specimens have a broken peristome (presence/absence of lip thickening not observable).

B. tarava n. sp. differs from B. megan n. sp. in its larger size height 2.92-3.75 mm vs heigh 2.40-2.70 mm in B. megan n. sp., higher height/width ratio 1.859 -1.807 vs 1.662 in B. megan ; more whorls 4-4.65 vs 3.20-3.50 in B. megan n. sp., less numerous axial ribs on the last whorl 11-14 (mean 12.6) vs 14-19 (mean 16.5) in B. megan n. sp., and its more slender protoconch with two fine spiral cordlets, with a large smooth median area, and a fine spiral cordlet below the abapical cordlets vs two fine spiral cordlets, the lower larger, a fine cordlet of microtubercles in the subsutural area and microtubercles over the entire surface in B. megan n. sp.

Figures

FIG. 18. — Benthonellania megan n. sp.: A-E, holotype,height 2.7 mm, width 1.6 mm Marquesas:MUSORSTOM 9 Stn DR1247 1150-1250 m 10°34’S,138°42’W, type locality, MNHN-IM-2000-37695; F-H, paratype, height 2.7 mm, width 1.6 mm, type locality, MNHN-IM-2000-37696; I-K, paratype, height 2.5 mm, width 1.475 mm, type locality, MNHN-IM-2000-37696. Scale bar: D, E, 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.