Parashiela rimatara 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 rimatara

description: Parashiela rimatara n. sp.
(Figs 30; 51C; 53L; Tables 4; 5; 6)
urn:lsid:zoobank.org:act: F4FD4FFA-0A9C-4905-B91D-53CA21E1CCC4
TYPE MATERIAL. — Holotype. Australes • dd (height 1.53 mm, width 1.00 mm, Figs 30 A-C, E-I, 53L); Rimatara, BENTHAUS Stn DW2021; 22°37’1”S, 152°48’36”W; 1200-1226 m; 25.XI.2002; MNHN-IM-2000-38716.
Paratype. Australes • 1 dd (height 1.33 mm, Fig. 30D); Rimatara, BENTHAUS Stn DW2020; 22°37’1”S, 152°49’1”W; 920-930 m; 25.XI.2002; MNHN-IM-2000-38717.
TYPE LOCALITY. — Australes: Rimatara, BENTHAUS Stn DW2021; 22°37’1”S, 152°49’1”W; 1200-1226 m.
OTHER MATERIAL EXAMINED. — Australes • 1 dd; S of Rurutu; BENTHAUS Stn DW2010; 22°31’58”S, 151°20’59”W; 520-950 m; 24.XI.2002; MNHN.
DISTRIBUTION AND SYMPATRY. — The species is at present known in the South Pacific Ocean from the Australes Islands (Rimatara, Rurutu) (Fig. 51C), where it is sympatric with P. ambulata Laseron, 1956 (Rimatara, Rurutu) and with P. expansilabrum n. sp. (Rimatara) (Table 5).
ETYMOLOGY. — The name is based on the type locality, Rimatara Island, used as a noun in apposition.
DIAGNOSIS. — Parashiela of medium size for the genus, height c. 1.50 mm. Protoconch multispiral. Teleoconch with numerous thin axial ribs, entering the umbilical fissure; convex, non angular whorls, macro spiral sculpture of only a thin suprasutural cordlets on the first whorl, vanishing on the last whorl. Microsculpture of dense spiral threads, some thicker and more marked. Peristome duplicated, with moderately thickened varix crossed by evident growth striae.
DESCRIPTION OF HOLOTYPE
Shell (Figs 30 A-C, E; 53L)
Medium size for the genus, height 1.53 mm, width 1.00 mm, height/width ratio 1.53, not very robust, ovate-conical.
Protoconch (Fig. 30F, G)
Multispiral, rather acute, of 1.4 whorls, height 0.185 mm, nucleus diameter 0.625 mm, first half whorl diameter 0.125 mm, maximum diameter 0.250 mm; protoconch I devoid of sculpture, protoconch II with only a thin spiral cordlet on the lower third. Protoconch I-II boundary very weak, sinuous (Fig. 30F, G). Protoconch-teleoconch boundary marked, with a sinusigera notch.
Teleoconch
Of 3.6 convex whorls, with barely evident double angle on the last whorl. Axial sculpture on the last whorl of 26 thin, flexuose, orthocline ribs, reaching the base and entering the umbilical fissure. Interspaces twice or three times as wide as the axial ribs. Macro spiral sculpture of only a weak and thin suprasutural cordlet on the first whorls, vanishing already from the penultimate whorl (Fig. 30F). Microsculpture of groups of 5-6 fine spiral threads, alternating with some thicker and more marked (Fig. 30H, I). Umbilical fissure evident. Aperture round-ovate height 0.65 mm, height/aperture height ratio 2.354, peristome duplicated; outer lip orthocline, sinuous, smooth internally, scarcely thickened externally, with numerous growth striae; columellar lip slightly angled.
Colour
Whitish colouration.
Operculum and soft parts
Unknown.
VARIABILITY
Only three specimens examined, all adults, not very variable in shape, but with a remarkable variation in the number of axial ribs on the last whorl, 26, 28 and 54 (Table 5 and Appendix 12).
REMARKS
Parashiela ambulata Laseron, 1956 differs from P. rimatara n. sp. in its more robust and larger shell (height 1.85 mm vs height 1.53 mm in P. rimatara n. sp.); in the whorl two medially angled with a spiral cordlet vs whorls with barely evident double angle, devoid of major spiral cordlets (only one minor suprasutural cordlet on the first whorls) in P. rimatara n. sp.; the umbilical fissure absent or very narrow, more evident in P. rimatara n. sp.
Parashiela invisibilis (Hedley, 1899) differs from P.rimatara n. sp. in the four spiral cordlets on the last whorl (2 above the aperture) vs only one minor suprasutural cordlet on the first whorls in P. rimatara n. sp.
Parashiela liddelliana (Hedley, 1907) differs from P.rimatara n. sp. in the lack of umbilical fissure, present in P. rimatara n. sp.; the smaller size (height 1.20 mm vs 1.38-1.53 mm in P. rimatara n. sp.); the fewer axial ribs with wider interspaces (c. 20 vs 26-54 in P. rimatara n. sp.).
Parashiela obesula n. sp. differs from P. rimatara n. sp. in its slightly more obtuse outline; the thinner and less acute ribs and the narrower umbilical fissure.
See under P. expansilabrum n. sp., P. rotundata n. sp. and 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 846-848, DOI: 10.5252/zoosystema2023v45a25, http://zenodo.org/record/10458066