Benthonellania maestratii, 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 : 373-377

Benthonellania maestratii n. sp.

( Figs 23 ; 24 A-C; 25G; 26O; Tables 1 ; 2)

urn:lsid:zoobank.org:act:B89A1D9D-C9AE-42A4-9F2E-B76C317DF351

TYPE MATERIAL. — Holotype. Australes • 1 dd (height 2.50 mm, width 1.62 mm, Figs 23 A-E, 24A-C); Récif Neilson , BENTHAUS Stn DW1925 ; 27°00’S, 146°05’W; 12.XI.2002; 560-790 m depth; MNHN-IM-2000-37704 .

TYPE LOCALITY. — Australes, Récif Neilson, BENTHAUS Stn DW1925; 27°00’S, 146°05’W; 560-790 m depth.

OTHER MATERIAL EXAMINED. — Australes • 3 dd; South coast of Rurutu, BENTHAUS Stn DW 2010; 22°32’S, 151°21’W; 24.XI. 2002; 520-950 m depth; MNHN .

DISTRIBUTION AND SYMPATRY. — The species is known in the South Pacific Ocean from the Australes (Récif Neilson, South coast of Rurutu), with only empty shells collected in 520-950 m depth ( Fig. 25G ).

Benthonellania maestratii n. sp. is sympatric with Benthonella boucheti n. sp., Benthonella communis n. sp., Benthonellania bouteti n. sp. and Benthonellania tuamotu n. sp. at the Australes (Récif Neilson, South coast of Rurutu); with Benthonellania tarava n. sp. and Benthonellania alis n. sp. at the Australes (South coast of Rurutu) ( Table 2).

ETYMOLOGY. — Named after Philippe Maestrati (MNHN), for his friendship and his long lasting, precious contribution to sample treating in the field and at the Muséum.

DESCRIPTION OF HOLOTYPE

Shell ( Figs 23 A-E; 24A-C)

Of medium size for the genus,height 2.50 mm width 1.625 mm, height/width ratio 1.538, not very solid, ovate-globose.

Protoconch ( Figs 23D, E ; 24B, C )

Multispiral, dome-shaped, of 2.3 whorls, height 0.325 mm, nucleus diameter 0.062 mm, first half whorl diameter 0.150 mm, maximum diameter 0.450 mm; protoconch I with 4 spiral threads interspaced by microtubercles more or less welded together ( Fig. 24C ), protoconch II with one abapical cordlet, the rest of surface covered with delicate lace-shaped structures, and two median with wavy spiral cordlets ( Fig. 24B ). Protoconch-teleoconch boundary marked.

Teleoconch

Of 3.2 convex whorls, suture non impressed, with clathrate sculpture. Height last whorl 1.75 mm, height/height last whorl ratio 1.428. Axial sculpture of 35 curved and opisthocline ribs on last whorl, well spaced c. 4 times narrower than interspaces, continuing through the columellar fissure. Varix broad, not thickened. Spiral sculpture on the last whorl of 22 cordlets not equidistant, narrower than axial ribs: 15 very fine adapical, 7 basal more spaced; others very fine spiral cordlets in the periumbilical area. Microsculpture of only growth striae. Umbilical chink present. Aperture subpyriform, simple, rounded, height 1.10 mm, height/ height aperture ratio 2.272, peristome continuous, outer lip weakly prosocline and slightly varicose, internally smooth. 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 14), only four specimens examined, two adults, one sub-adult and one juvenile. Maximum dimensions: height 3.13 mm, width 2.05 mm (from South coast of Rurutu). The number of axial ribs and spiral cordlets on the last whorl, are respectively 35-57 and 22-35.

REMARKS

Benthonellania maestratii n. sp. resembles some European species of Alvania : A. stenolopha Bouchet & Warén, 1993 , A. adiaphoros Bouchet & Warén, 1993 , A. microstriata Hoenselaar & Goud, 1998 and A. seinensis Gofas, 2007 . It is easily distinguished from all those species, in its more convex whorls and the multispiral protoconch of 2.25-2.3 whorls vs paucispiral protoconch of 1.4, 1.5, 0.9-1.0 and 1.25 whorls respectively (see Bouchet & Warén 1993: 652-653, figs 1447, 1482-1487, 1516; Hoenselaar & Goud 1998: 91, figs 44-47; Gofas 2007: 795, figs 7E-H).

Alvania nicobarica ( Thiele,1925) [described as Rissoa (Alvania) nicobarica by Thiele (1925: 86, pl. 6, fig. 30) ( MolluscaBase 2021f)] differs from B. maestratii n. sp. for the smaller size (0.95 mm in height and 0.7 mm in width vs 2.5-3.12 mm and 1.62-2.07 in width in B. maestratii n. sp.), the lower height/ width ratio (1.357 vs 1.507 -1.538 in B. maestratii n. sp.) and for the protoconch described without sculpture vs protoconch with abapical cordlets and microsculpture in B. maestratii n. sp.

Benthonellania listera ( Dall, 1927) [ Rissoa listera Dall, 1927: 117 ], from the Atlantic Ocean differs from B. maestratii n. sp. in its more slender outline with less convex whorls; the crown formed by the subsutural thickening of the axial ribs vs absent in B. maestratii n. sp.; the umbilical chink absent vs present in B. maestratii n. sp. (see also the drawing of one syntype by Moolenbeek & Faber 1991: 53).

Benthonellania maestratii n. sp. is also similar to Benthonellania colombiana ( Romer & Moore, 1988) n. comb., but the latter differs in its smaller size (height 1-1.3 mm vs height 2.5-3.13 mm in B. maestratii n. sp.), fewer axial ribs (26 vs 35-57 in B. maestratii n. sp.), different spiral sculpture (subsutural groove and 7-9 cords vs 22-35 fine cords in B. maestratii n. sp.); protoconch with two spiral cordlets, one finer and median, the other suprasutural with a zigzagging pattern, and with tubercles scattered over the entire surface vs protoconch II with abapical cordlet, the rest of surface covered with delicate lace-shaped structures with wavy and oblique spirals in B. maestratii n. sp.

Figures

FIG. 23. —Benthonellania maestratii n. sp.: A-E, holotype, height 2.50 mm width 1.62 mm, Australes: BENTHAUS Stn DW1925, 560-790 m, type locality, MNHN- IM-2000-37704; F, G, height 3.12 mm, width 2.07 mm, Australes: BENTHAUS Stn DW2010, 520-950 m depth, 22°32’S, 151°21’W; H, height 2.8 mm, width 1.85 mm, Australes: BENTHAUS Stn DW2010, 520-950 m depth, 22°32’S, 151°21’W. Scale bars: D, E, 0.25 mm.

FIG. 24. — Benthonellania maestratii n. sp. (SEM): A-C, holotype, height 2.50 mm, Australes, MNHN-IM-2000-37704: shell (A); detail of the protoconch microsculture (B, C). Scale bars: B, 40 μm; C, 100 μm.

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.