Parashiela expansilabrum 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 expansilabrum

description: Parashiela expansilabrum n. sp.
(Figs 28; 51B; 53J; Tables 4; 5; 6)
urn:lsid:zoobank.org:act: D94A2A08-7D06-40A9-B53B-072CB33E48C7
Parashiela sp. 2 – Boutet et al. 2020: 240.
TYPE MATERIAL. — Holotype. Australes • dd (height 1.47 mm, width 1.00 mm, Figs 28 A-C, F-J; 53J); Rimatara, BENTHAUS Stn DW 2020; 22°37’1”S, 152°49’1”W; 920-930 m; 25.XI.2002; MNHN-IM-2000-38712.
Paratype. Australes • 1 dd; same locality data as holotype; MNHN- IM-2000-38713.
TYPE LOCALITY. — Australes: Rimatara, BENTHAUS Stn DW 2020; 22°37’1”S, 152°49’1”W; 920- 930 m.
OTHER MATERIAL EXAMINED. — Society Islands • 3 dd; Tahiti, Tiarei; 17°32’34”S, 149°20’27”W; <1 m depth; fringing reef flat; coll. JL • 6 dd; Tahiti, Arue, Matavai Bay; 17°31’1”S, 149°30’35”W; 16 m depth; coll. JL • 4 dd; Tahiti, Faille d’Arue; 17°31’1”S, 149°31’30”W; 15-61 m depth; coll. JL • 5 dd; Tahiti, Motu Uta; 17°31’51”S, 149°34’51”W; 20 m; wreck, behind breakwater; coll. JL • 1 dd; Moorea; 17°34’1”S, 149°46’58”W; 85 m; coll. JL • 1 dd; Huahine, TARASOC Stn DW3426; 16°40’58”S, 151°3’0”W; 801- 874 m; MNHN • 1 dd; Raiatea; 16°44’27”S, 151°30’21”W; 85 m; outer slope; coll. MB.
Tuamotu • 2 dd; Makemo, Passe Arikitamiro; 16°37’15”S, 143°33’50”W; 47-54 m; coll. JL • 1 dd; Rangiroa, Passe Tiputa; 14°58’1”S, 147°37’33”W; 100 m; coll. JL.
Australes • 1 dd; Rurutu, Vitaria; 22°28’44”S, 151°21’14”W; 51 m; coll. JL.
DISTRIBUTION AND SYMPATRY. — The species is known from the South Pacific Ocean in the Australes (Rurutu, Rimatara), Society Islands (Tahiti, Moorea, Huahine), Tuamotu (Makemo, Rangiroa), with only empty shells collected at 1-100 m depth, but also at 801- 930 m depth; we consider that the deeper samples were carried downslope from upper habitats, all known Parashiela being rather shallow water species. (Fig. 51B).
Parashiela expansilabrum n. sp. is sympatric with P. rimatara n. sp. in the Australes (Rimatara); with P. ambulata Laseron, 1956 in the Australes (Rimatara), Tuamotu (Makemo), Society (Tahiti); with P. obesula n. sp. in the Australes (Rurutu) (Table 5).
ETYMOLOGY. — For the particular conformation of the aperture, from the Latin expansus – expanded, labrum – lip. Used as a noun in apposition.
DIAGNOSIS. — Parashiela of medium size for the genus, height <1.55 mm. Protoconch multispiral. Teleoconch with flexuose axial ribs, rather robust for the genus, reaching the base and entering the narrow umbilical fissure; whorls with a weak triple anglulation on the last whorl. Spiral sculpture of only a thin suprasutural cordlet on the first whorl, changing into a weak angulation in subsequent whorls. Dense microsculpture of spirally arranged microgranules. Peristome duplicated, with thick and broad varix crossed by evident growth striae.
DESCRIPTION OF HOLOTYPE
Shell (Figs 28 A-C, F-J; 53J)
Medium size for the genus, height 1.47 mm, width 1.00 mm, height/width ratio 1.47, rather robust, ovate-conical.
Protoconch (Fig. 28G, H)
Multispiral, low, of 1.30 whorls, height 0.200 mm, nucleus diameter 0.100 mm, first half whorl diameter 0.162 mm, maximum diameter 0.237 mm; protoconch I and protoconch II almost smooth, with a thin spiral thread on the lower third. Protoconch I-II boundary weak, sinuous (Fig. 28G, H).
Protoconch-teleoconch boundary marked, with a sinusigera notch.
Teleoconch
Of 3.25 convex whorls with slight shoulder on upper whorls and a triple slight angle on last whorl. Axial sculpture on last whorl of 18 thin ribs, robust for the genus, flexuose, slightly prosocline, reaching the base and entering the narrow umbilical fissure. Interspaces twice to three times as wide as the axial ribs. Macro spiral sculpture of only a weak and thin suprasutural cordlet on the first whorl, changing into a weak angulation in subsequent whorls. Microsculpture of spirally arranged microgranules. (Fig. 28I, J). Umbilical fissure evident, narrow. Aperture ovate-piriform, height 0.67 mm, height/aperture height ratio 2.19, with continuous duplicated peristome; outer lip orthocline, sinuous, smooth internally, very expanded and thickened, with numerous growth striae; columellar lip slightly angled.
Colour
Colouration whitish.
Operculum and soft parts
Unknown.
VARIABILITY
Size:minimum adult height: 1.12 mm (fromTahiti), maximum: 1.55 mm (from Tuamotu) (see Table 4 and Appendix 10).
REMARKS
Parashiela invisibilis differs from P. expansilabrum n. sp. in the presence of spiral cordlets on the whorls, absent in P. expansilabrum n. sp., and in a higher height/width ratio (1.67 vs 1.33-1.47 in P. expansilabrum n. sp.).
Parashiela liddelliana differs from P. expansilabrum n. sp. in its more slender shell with a broader shoulder; in its smaller aperture without any expansion of the outer lip; in the narrower last whorl, base, and umbilical fissure.
Parashiela ambulata differs from P. expansilabrum n. sp. in the presence of spiral cordlets on the whorls, absent in P. expansilabrum n. sp.
Parashiela rimatara n. sp. differs from P. expansilabrum n. sp. in its more slender and delicate shell; in the axial ribs thinner and more numerous (26-54 vs 18-24 in P. expansilabrum n. sp.); in the higher height/width ratio (1.53 vs 1.33-1.47 in P. expansilabrum n. sp.), narrower interspaces, narrower labial varix without any expansion of the lip; in the lack of angles at the body-whorls vs three weak angles on the last whorl in P. expansilabrum n. sp.
See under P. soniae 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 843-845, DOI: 10.5252/zoosystema2023v45a25, http://zenodo.org/record/10458066