Parashiela obesula Amati & Giulio & Oliverio 2023, n. sp.
Creators: name: Amati, Bruno
name: Giulio, Andrea Di
name: Oliverio, Marco
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Littorinimorpha
Rissoidae
Parashiela
Parashiela obesula

description: 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.
description: Published as part of 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, pp. 803-892 in Zoosystema 45 (25) on pages 845-846, DOI: 10.5252/zoosystema2023v45a25, http://zenodo.org/record/10458066