Parashiela obesula, 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 : 845-846

Parashiela obesula n. sp.

( Figs 29 ; 51C ; 53K ; Tables 4 ; 5; 6)

urn:lsid:zoobank.org:act:8E9BA374-355A-4140-AA62-97657B1A62F5

TYPE MATERIAL. — Holotype. Australes • dd (height 1.32 mm, width 0.88 mm, Figs 29 ; 53K ); S of Rurutu , BENTHAUS Stn DW2010; 22°31’58”S, 151°20’59”W; 520-950 m; 24.XI.2002; MNHN-IM-2000-38714 .

Paratypes. Australes • 2 dd; same locality data as holotype; MNHN- IM-2000-38715 .

TYPE LOCALITY. — Australes: S of Rurutu; BENTHAUS Stn DW2010; 22°31’58”S, 151°20’59”W; 520- 950 m.

DISTRIBUTION AND SYMPATRY. — The species is at present known in the South Pacific Ocean from the Australes (Rurutu) ( Fig. 51C ), where it is sympatric with P. ambulata Laseron, 1956 and P. expansilabrum n. sp. ( Table 5 ).

ETYMOLOGY. — From the Latin obesus, -a, -um meaning plump or fat, referring to the plump outline (- ula is a diminutive suffix).

DIAGNOSIS. — Parashiela small for the genus, height 1.07-1.32 mm. Protoconch multispiral. Teleoconch with numerous, thin axial ribs, entering the umbilical fissure; convex whorls with no angles, macro spiral sculpture of only a thin suprasutural cordlets on the first whorl, vanishing on the second whorl. Microsculpture of dense spiral threads, some more marked. Peristome duplicated, with moderately thickened varix crossed by evident growth striae.

DESCRIPTION OF HOLOTYPE

Shell ( Figs 29 A-D; 53K)

Small for the genus, height 1.32 mm, width 0.88 mm, height/ width ratio 1.50, rather robust, ovate-conical.

Protoconch ( Fig. 29E, F )

Multispiral,dome-shaped, of1.35 whorls, height 0.200mm, nucleus diameter 0.063 mm, first half whorl diameter 0.137 mm, maximum diameter 0.250 mm; protoconch I devoid of sculpture, protoconch II with only a thin spiral cordlet on lower third and microtubercles on the abapical area ( Fig. 29F ). Protoconch I-II boundary weak, sinuous. Protoconch-teleoconch boundary marked, with a sinusigera notch.

Teleoconch

Of 3.15 convex whorls, with a weak cordlet on the first whorl, fading and eventually disappearing on the second whorl. Axial sculpture on the last whorl of 37 thin, flexuose, slightly prosocline ribs, reaching the base and entering the umbilical fissure. Interspaces twice as wide as axial ribs, sculptured by numerous spiral threads, some thicker and more marked ( Fig. 29G ). Very narrow umbilical fissure. Aperture ovate-piriform height 0.58 mm, height/aperture height ratio 2.28; peristome continuous, duplicated; outer lip prosocline, slightly sinuous, smooth internally, externally expanded and very thickened, with numerous growth striae; columellar lip slightly angled medially.

Colour

Whitish colouration.

Operculum and soft parts

Unknown.

VARIABILITY

Only three specimens examined, all adults: no significant variation detected (see Table 5 and Appendix 11).

REMARKS

See under P. rimatara n. sp. and P. rotundata n. sp. for detailed comparisons.

Figures

FIG. 29. — Parashiela obesula n. sp.: holotype. Australes, Rurutu,Stn BENTHAUS DW2010, 520-950 m, height 1.32 mm, width 0.88 mm, MNHN-IM-2000-38714: A-D, shell; E, F, detail of the first whorls; G, detail of the microsculpture of the teleoconch. Scale bars: E, 40 μm, F, G 10 μm.

FIG. 51. — Distribution maps of the Polynesian species of Haurakia Iredale,1915, and Parashiela Laseron, 1956: A, Haurakia marmorata (Hedley,1907); B, Parashiela ambulata Laseron, 1956; C, Parashiela expansilabrum n. sp.; D, Parashiela obesula n. sp. (*), Parashiela rimatara n. sp. (○), Parashiela rotundata n. sp. (●), Parashiela soniae 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.