Subestea moruroa, 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 : 872-874

Subestea moruroa n. sp.

( Figs 46A ; 47 ; 52D ; 53U ; Tables 7 ; 10 )

urn:lsid:zoobank.org:act:4FBB581D-CB71-4188-988F-C0956F9A2A45

Pusillina sp. – Boutet et al. 2020: 240.

TYPE MATERIAL. — Holotype. Tuamotu • dd (height 1.96 mm, width 1.02 mm, Figs 46 A-C; 47; 53U); Moruroa ; 21°46’37”S, 138°53’31”W; beached; on the sea-line; MNHN-IM-2000-38732 .

Paratype. Tuamotu • 1 dd; Moruroa ; same data as holotype; MNHN-IM-2000-29047

TYPE LOCALITY. — Tuamotu; Moruroa; 21°46’37”S, 138°53’31”W; on the sea-line.

OTHER MATERIAL EXAMINED. — Tuamotu • 10 dd; Pinaki; 19°23’56”S, 138°40’1”W; beached; sediment on reef flat; coll. JL • 9 dd; Nukutavake; 19°16’37”S, 138°46’30”W; beached; sediment on reef flat; coll. JL • 2 dd ( Fig. 46D, E ); Ana’a, Tukuhora; 17°20’41”S, 145°31’26”W; 1-2 m; lagoon; coll. MB • 12 dd; Makemo, Pouheva; 16°37’22”S, 143°35’34”W; 1 m; reef edge behind lighthouse; coll. JL • 8 dd; Makemo, Passe Arikitamiro, Nake; 16°37’1”S, 143°33’43”W; <1 m; reef edge; coll. JL • 10 dd; Raroia; 16°2’9”S, 142°28’37”W; <1 m; reef edge; coll. JL • 8 dd; Fangatau; 15°49’8”S, 140°53’9”W; beached; sediment on reef flat; coll. JL. Gambier • 1 dd; Mangareva, Rikitea; 23°6’39”S, 134°58’1”W; beached; beached sediment; coll. JL • 2 dd; Tenoko; 23°4’26”S, 135°0’35”W; 1-3 m; coll.JL • 2 dd; Totegegi; 23°5’2”S, 134°52’58”W; 1-3 m; beached sediment; coll. JL.

DISTRIBUTION AND SYMPATRY. — Subestea moruroa n. sp. is known from the South Pacific Ocean, in the Tuamotu (Moruroa, Pinaki, Nukutavake, Ana’a, Makemo, Raroia, Fangatau) and Gambier ( Fig. 52D ).

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

DIAGNOSIS. — Subestea with medium sized shell (<2 mm height), robust, slender; protoconch paucispiral, dome-shaped; teleoconch with axial ribs broader but weaker than spirals; convex and angled whorls; marked teleoconch microsculpture; colouration uniform white, occasionally with two spiral series of false blotches (difference in shell transparency).

DESCRIPTION OF HOLOTYPE

Shell ( Figs 46 A-C; 47A; 53U)

Small for the genus, height 1.96 mm, width 1.02 mm, height/ width ratio 1.92, robust, elongate-conic.

Protoconch ( Fig. 47 B-D)

Paucispiral, dome-shaped, of 1.5 slightly convex whorls, height 0.237 mm, nucleus diameter 0.112 mm, first half whorl diameter 0.212 mm, maximum diameter 0.287 mm, with 8 thin spiral cordlets, interspaced by dense series of minute pits ( Fig. 47C, D ). Protoconch-teleoconch boundary well marked.

Teleoconch

Of 3.50 convex whorls, angled in the median part, suture shallow. Axial sculpture on the last whorl of 9 slightly prosocline ribs not reaching the base. Spiral sculpture of 15 unequal and unequally spaced spiral cordlets, narrower than interspaces, 9 above the aperture.Three starting after protoconch-teleoconch boundary.

Microsculpture of raised spiral threads, interspaced by axial riblets ( Fig. 47 E-G).Umbilical fissure absent. Aperture roundedpiriform, height 0.72 mm, height/aperture height ratio 2.72, peristome continuous, outer lip with slightly thickened varix and sharp edge, prosocline, internally smooth.

Colour

Uniform white.

Operculum and soft parts

Unknown.

VARIABILITY

We examined 66 not particularly fresh specimens (including adults and juveniles). Size ranges from 1.25 mm (from Makemo) to 1.96 mm (from Moruroa).

Species with some variation only in the H/W ratio (1.63- 2.00) and in the strength of the axial ribs, which in many specimens are very flattened especially on the last whorl (see Table 8 and Appendix 22). Some specimens show two spiral series of transparent blotches on an otherwise opaque shell.

REMARKS

Subestea moruroa n. sp. differs from Subestea australiae ( Frauenfeld, 1867) , from Sydney, Southeast Australia ( Frauenfeld 1867: 14, pl. II, fig. 23; Ponder 1985: 164, pl. 115, fig. A-E), in its more acute spire, the more angled whorls, and the less rounded aperture; in the protoconch with eight thin spiral cordlets, interspaced by dense series of minute pits vs six broader spiral cordlets, interspaced by microtubercles in S. autraliae .

Subestea moruroa n. sp. differs from Subestea alfredensis ( Bartsch, 1915) , from South Africa ( Bartsch 1915: 128, pl. 21, fig. 8; Ponder 1985: 164, pl. 115, fig. F-H), in the presence of an axial sculpture and in the spiral sculpture with 15 cordlets on the last whorl (nine above the aperture) of different and unequal thicknesses vs 22 thinner and equidistant cordlets (13 above the aperture) in S. alfredensis ; in the more acute spire and more elongated aperture; in the protoconch with eight thin spiral cordlets, interspaced by dense series of micropits vs spiral cordlets as wide as the deep interspaces, the latter sculptured by microtubercles in S. alfredensis .

Subestea moruroa n. sp. differs from Subestea glypta (E. A. Smith, 1890) , from St. Helena Island, Eastern Atlantic (E. A. Smith 1890: 288, pl. 23, fig. 39; https://www.molluscabase. org/aphia.php?p=taxdetails&id=988087, photo of a syntype), in the more robust axial ribs, almost absent in S. glypta ; in the fewer spiral cordlets on the last whorl (15, of which nine above the aperture) vs thinner and more numerous (21, of which 11 above the aperture) in S. glypta .

Subestea platia (E. A. Smith, 1890) from St. Helena Island, Eastern Atlantic (E. A. Smith 1890: 309, pl. 24, fig. 13), is very similar to the sympatric Subestea glypta . Subestea moruroa n. sp. differs from it in the first whorls being more slender and more angulated.

Subestea moruroa n. sp. differs from Subestea lusciniae (R. B. Watson, 1886) from Nightingale Island, Tristan da Cunha group, South Atlantic (R. B. Watson 1886: 597, pl. 44, fig. 3), in the presence of a weak angulation of the whorls, absent in S. lusciniae ; in the presence of axial ribs also on the last whorl, absent or weak in S. lusciniae ; in the fewer axial ribs on the penultimate whorl, 10 vs 16 in S. lusciniae ; in the more numerous spiral cordlets on the last whorl (15, of which nine above the aperture), with different and unequal thicknesses vs nine, of which three above the aperture in S. lusciniae .

CLUSTER ANALYSIS

An UPGMA cluster analysis was performed on a similarity matrix (Jaccard index) based on presence/absence of the studied species in each archipelago plus the Tarava Seamounts. The resulting tree is reported in Figure 53 . Among the archipelagos, Tuamotu and Society resulted the most similar, followed by Australes, Gambier and Marquesas; the Tarava Seamounts were the least similar, due to the single species from that area included in this study.

Figures

FIG. 46. — Subestea moruroa n. sp.: A-C, holotype, Tuamotu, Moruroa, on the sea-line, height 1.96 mm, MNHN-IM-2000-38732; D, E, Ana’a, Tukuhora; 1-2 m, height 1.57 mm, Coll. MB: shell (D), detail of the first whorls (E). Scale bar: E, 25 μm.

FIG. 47. — Subestea moruroa n. sp. SEM.: holotype Tuamotu, Moruroa, on the sea-line, height 1.96 mm, MNHN-IM-2000-38730: A, shell; B, detail of the protoconch); C, D, detail of the microsculpture of the protoconch; E-G, detail of the microsculpture of the teleoconch. Scale bars: B, 100 μm, C, F, 10 μm, D, 2 μm, E, 100 μm, G, 1 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.