Simulamerelina tuamotu, Amati & Giulio & Oliverio, 2023

Amati, Bruno, Giulio, Andrea Di & Oliverio, Marco, 2023, Shallow-water Rissoidae of the genera Alvania Risso 1826 Haurakia Iredale 1915 Parashiela Laseron 1956 Simulamerelina Ponder 1985 and Subestea Cotton 1944 Gastropoda Caenogastropoda Rissooidea from French Polynesia with the description of a new deep-water genus, Zoosystema 45 (25), pp. 803-892 : 868-871

Simulamerelina tuamotu n. sp.

( Figs 44 ; 45 ; 52C ; 53T ; Tables 7 ; 8 ; 9 )

urn:lsid:zoobank.org:act:9CFA60AC-901A-421E-92D2-428F9B62CE43

Simulamerelina sp. 5 – Boutet et al. 2020: 240.

TYPE MATERIAL. — Holotype. Tuamotu • dd (height 1.57 mm, width 0.90 mm, Figs 44 A-C; 45; 53T); Makemo , Passe Arikitamiro , Nake ; 16°37’1”S, 143°33’43”W; <1 m; reef flat; MNHN-IM-2000-38730 .

Paratypes. Tuamotu • 10 dd ( Fig. 44D, E ); same locality data as holotype; MNHN-IM-2000-38731 .

TYPE LOCALITY. — Tuamotu: Makemo, Passe Arikitamiro, Nake; 16°37’1”S, 143°33’43”W; <1 m.

OTHER MATERIAL EXAMINED. — Tuamotu • 9 dd; Makemo, Passe Arikitamiro; 16°37’15”S, 143°33’50”W; 45-54 m; coll. JL (8), coll. MB (1).

DISTRIBUTION AND SYMPATRY. — Simulamerelina tuamotu n. sp. is known only for the Tuamotu (Makemo) ( Fig. 52C ).

No congener collected sympatrically.

ETYMOLOGY. — From the type locality, Tuamotu, used as a noun in apposition.

DIAGNOSIS. — Simulamerelina with shell small for the genus (<2 mm), slender,turriculated, robust.Protoconch paucispiral with markedly twisted nucleus; outline turriculate-pagodiform, with deep canaliculated suture; axials and spirals forming at their intersection, spiny tubercles. Central cordlet larger and protruding. Axial ribs not reaching the base. Start of 3 spiral cordlets, the subsutural weaker, after protoconch-teleoconch boundary. Entire surface covered by distributed spiral threads, more spaced in the interspaces of spiral cordlets. Colouration uniform white.

DESCRIPTION OF HOLOTYPE

Shell ( Figs 44 A-C; 45A; 53T)

Small for the genus, height 1.57 mm, width 0.90 mm height/ width ratio 1.74, turriculate-pagodiform, elongate ovate.

Protoconch ( Fig. 45B )

Paucispiral with slightly twisted nucleus, of 1.25 convex whorls, height 0.300 mm, nucleus diameter 0.070 mm, first half whorl diameter 0.167 mm, maximum diameter 0.275 mm. Sculpture of one strong adapical spiral keel, and minute granules over the entire surface. Protoconch-teleoconch boundary well marked.

Teleoconch

Of 3.25 convex whorls, suture canaliculated. Axial sculpture on the last whorl of 10 orthocline ribs, thinner than the interspaces and sharply interrupted at the base. Spiral cordlets of same thickness as axials: 2 on the first whorl, three on the next whorls and 3 above the aperture, 8 on the last whorl; cord I weaker, cord II larger and more protruding; 5 basal cords thinner and more closely spaced. Spiny tubercles at intersections; interspaces quadrangular.

Microsculpture ( Fig. 45C ) of dense spiral threads, more spaced in the interspaces of the spirals. Umbilical fissure absent. Aperture oval, height 0.53 mm, height/aperture height ratio 2.96, peristome duplicated, internally smooth, externally thickened by a strong prosocline varix.

Colour

Colouration uniform white.

Operculum and soft parts

Unknown.

VARIABILITY

Height ranging 1.25-1.65 mm. Outer lip orthocline, slightly prosocline or slightly opisthocline (seeTable 8 and Appendix 21).

REMARKS

Simulamerelina wanawana ( Kay, 1979) , from Barbers Point, Oahu, Hawaii ( Kay 1979: 82, pl. 28, fig. A, B) differs from S. tuamotu n. sp. in its larger size (height 1.75 in the holotype vs height 1.25-1.65 mm in S. tuamotu n. sp.) and the higher height/width ratio (2.33 vs 1.56-1.77 in S. tuamotu n. sp.); in the spiral sculpture of two cords of equal thickness above the aperture vs three cords, of which the subsutural weaker and the median (II) larger and more protruding; the protoconch of 1.5 whorls vs 1.2-1.25 whorls in S. tuamotu n. sp.

Simulamerelina longinqua ( Rehder, 1980) , from Easter Island ( Rehder 1980: 29, pl. 5, fig. 10), differs from S. tuamotu n. sp. in its larger size (height 1.8-2.01 mm vs 1.25-1.65 mm in S. tuamotu ); the colouration yellowish white vs uniform white in S. tuamotu n. sp.; the protoconch with two or three spiral cords vs one strong adapical spiral keel, and minute granules over the entire surface in S. tuamotu n. sp.; the fewer spiral cordlets on the base (3 vs 4-5 in S. tuamotu ); the spiral cordlets above aperture all of the same thickness vs three cords, of which the subsutural weaker and the median (II) larger and more protruding in S. tuamotu n. sp.

Merelina lacunosa ( Powell, 1940) from Tom Bowling Bay, northern New Zealand ( Powell 1940: 227, pl. 30, fig. 9), recalls S. tuamotu n. sp., in its teleoconch sculpture initially consisting, in both species, of two spiral cordlets of which the central more protruding and the lower, suprasubsutural progressively weaker; it can however be easily distinguished by the apical sculpture typical of the genus Merelina Iredale, 1915 , with spiral cordlets vs with one strong spiral adapical keel, and minute granules over the entire surface in S. tuamotu n. sp.; the larger size (height> 2 mm vs height <2 mm in S. tuamotu n. sp.) and higher height/width ratio (2.10 vs 1.56- 1.77 S . tuamotu n. sp.); and for the different colouration (uniform brown vs uniform white in S. tuamotu n. sp.).

See under Simulamerelina micrometrica n. sp. for detailed comparisons.

Figures

FIG. 44. — Simulamerelina tuamotu n. sp.: A-C, holotype, Tuamotu, Makemo, Nake, <1 m, height 1.57 mm, width 0.90 mm, MNHN-IM-2000-38730; D, paratype, Tuamotu,Makemo, Nake, <1 m, height 1.58 mm, MNHN-IM-2000-38731; E, paratype, Tuamotu, Makemo,Nake, <1 m, height 1.27 mm, MNHN-IM-2000-38731.

FIG. 45. — Simulamerelina tuamotu n. sp.: holotype, Tuamotu, Makemo, Nake, <1 m, MNHN-IM-2000-38730: A, shell, height 1.57 mm, width 0.90 mm; B, detail of the first whorls; C, detail of the microsculpture of the second whorl (MNHN-IM-2000-38730). Scale bars: B, 100 μm, C, 30 μm.

FIG. 52. — Distribution maps of the Polynesian species of Simulamerelina Ponder, 1985 and Subestea Cotton, 1944: A, Simulamerelina australes n. sp.; B, Simulamerelina densestriata n. sp. (○), Simulamerelina gracilis n. sp. (●), Simulamerelina lepteseiras n. sp. (✩); C, Simulamerelina micrometrica n. sp. (○), Simulamerelina tuamotu n. sp. (●); D, Subestea moruroa n. sp. (○).

FIG. 53. — Alvania Risso,1826,Ellenstrongia n. gen., Haurakia Iredale,1915,Parashiela Laseron,1956,Simulamerelina Ponder,1985 and Substea Cotton,1944:A, Alvania letouneuxi n.sp., holotype,MNHN-IM-2000 38703, height 1.60 mm; B, Alvania herosae n. sp., holotype,MNHN-IM-2000-38704, height 2.02 mm;C, Alvania herosae n.sp.(morph B),MNHN,height 2.16 mm;D, Alvania parvimaculata n. sp.,holotype,MNHN-IM-2000-38706, height 1.65 mm;E, Alvania prosocostata n.sp., holotype, MNHN-IM-2000-38708 height 2.05 mm; F, Alvania uapou n. sp., holotype, MNHN-IM-2000-38710, height 1.70 mm; G, Ellenstrongia tarasoc n. gen., n. sp., holotype,MNHN-IM-2000-39448, height 4.50 mm; H, Haurakia marmorata (Hedley, 1907), Society Islands,height 1.95 mm, coll. JL; I, Parashiela ambulata Laseron, 1956, Australes: Rapa Pointe Kauira, height 1.60 mm, MNHN; J, Parashiela expansilabrum n. sp. holotype, MNHN-IM-2000-38712 height 1.47 mm; K, Parashiela obesula n. sp. holotype, MNHN-IM-2000-38714, height 1.32 mm; L, Parashiela rimatara n. sp. holotype, MNHN-IM-2000-38716, height 1.47 mm; M, Parashiela rotundata n. sp. holotype, MNHN-IM-200038718-, height 1.10 mm; N, Parashiela soniae n. sp., holotype, MNHN-IM-2000-38720, height 1.17 mm; O, Simulamerelina australes n. sp. holotype, MNHN-IM-2000-38722, height 2.47 mm; P, Simulamerelina densestriata n. sp., holotype, MNHN-IM-2000-38724, height 2.45 mm; Q, Simulamerelina gracilis n. sp., holotype, MNHN-IM-2000-38726, height 2.45 mm; R, Simulamerelina lepteseiras n. sp., holotype, MNHN- IM-2000-38727, height 1.47 mm; S, Simulamerelina micrometrica n. sp., holotype, MNHN-IM-2000-38728, height 1.33 mm; T, Simulamerelina tuamotu n. sp. holotype, MNHN-IM-2000-38730, height 1.57 mm; U, Subestea moruroa n. sp., holotype, MNHN-IM-2000-38732, height 1.96 mm.