Parashiela rotundata 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 rotundata

description: Parashiela rotundata n. sp.
(Figs 31; 51C; 53M; Tables 4; 5; 6)
urn:lsid:zoobank.org:act: EA50A8A2- ACE 6-436B-B867-65EF828766AC
TYPE MATERIAL. — Holotype. Society Islands • dd (height 1.10 mm, width 0.77 mm, Figs 31, 53M) • Tahiti, Arue, Matavai Bay; 17°31’1”S, 149°30’35”W; 16-25 m; J. Letourneux leg.; MNHN-IM-2000-38718.
Paratypes. Society Islands • 5 dd; same locality data as holotype; MNHN-IM-2000-38719.
TYPE LOCALITY. — Society Islands: Tahiti, Arue, Matavai Bay; 17°31’1”S, 149°30’35”W; 16- 25 m.
OTHER MATERIAL EXAMINED. — Society Islands • 35 dd; Tahiti, Tiarei; 17°32’34”S, 149°20’27”W; <1 m; fringing reef flat; coll. JL • 27 dd; Tahiti, Papeete, Motu Uta; 17°31’51”S, 149°34’51”W; 20 m; wreck, behind breakwater; coll. JL • 20 dd; Moorea; 17°34’1”S, 149°46’58”W; 85 m; coll. JL.
Tuamotu • 4 dd; Makemo, Passe Arikitamiro; 16°37’15”S, 143°33’50”W; 47-54 m; coll. JL • 4 dd; Rangiroa, Passe Tiputa; 14°58’1”S, 147°37’12”W 6; 100 m; coll. JL.
DISTRIBUTION AND SYMPATRY. — The species is at present known in the South Pacific Ocean from Society Islands (Tahiti, Moorea) in <1-85 m, and the Tuamotu (Makemo, Rangiroa) in 47-100 m (Fig. 51C).
Parashiela rotundata n. sp. is sympatric with P. expansilabrum n. sp. in the Society (Tahiti) and the Tuamotu (Makemo, Rangiroa); with P. ambulata (Laseron, 1956) in the Society (Tahiti) and the Tuamotu (Makemo) (Table 6).
ETYMOLOGY. — Referring to the rounded outline, from the Latin rotundatus, -a, -um, rounded.
DIAGNOSIS. — Parashiela of small size for the genus, height c. 1 mm. Protoconch multispiral. Teleoconch with numerous, thin and low axial ribs, only a partly of them entering the umbilical fissure; convex whorls with no angles, absence of macro spiral sculpture. Microsculpture of groups of 3-4 thin threads, separated by micro furrows. Peristome duplicated, with moderately thickened varix, crossed by evident growth striae.
DESCRIPTION OF HOLOTYPE
Shell (Figs 31 A-D; 53M)
Small for the genus, height 1.10 mm, width 0.77 mm, height/ width ratio 1.43, rather robust, ovate-conical.
Protoconch (Fig. 31E, F)
Multispiral, low, of 1.35 whorls, height 0.162 mm, nucleus diameter 0.062 mm, first half whorl diameter 0.137 mm, maximum diameter 0.262 mm; protoconch I devoid of sculpture, protoconch II with only a thin spiral cordlet on the lower third. Protoconch I-II boundary weak, sinuous. Protoconch-teleoconch boundary marked, with a sinusigera notch (Fig. 31E).
Teleoconch
Of 2.75 convex whorls. Axial sculpture on the last whorl of 26 thin, flexuose, slightly prosocline ribs, only half of them (every other one) reaching the base and entering the umbilical fissure; interspaces three times as wide as axial ribs. Spiral microsculpture of groups of 3-4 thin threads, separated by micro furrows (Fig. 31G). Umbilical fissure open. Aperture ovate-piriform height 0.50 mm, height/ aperture height ratio 2.20, with peristome duplicated; outer lip prosocline, slightly sinuous, internally smooth, externally very thickened and with numerous growth striae; columellar lip slightly angular.
Colour
Colouration white.
Operculum and soft parts
Unknown.
VARIABILITY
Species not very variable (See Table 5 and Appendix 13).
REMARKS
Parashiela obesula n. sp. differs from P. rotundata n. sp. in its narrower base and umbilical fissure; the more numerous axial ribs (37-41 vs 26-34 in P.rotundata n. sp.); the microsculpture of groups of 5-6 thin striae vs groups of 3-4 thin striae divided by microfurrows in P. rotundata n. sp.; the higher protoconch. Parashiela rimatara n. sp. differs from P. rotundata n. sp. in the larger size (height 1.38-1.53 mm vs 0.81-1.17 mm in P. rotundata n. sp.); the less convex whorls; the axial ribs all entering the umbilical fissure vs half of the ribs (every two) not reaching the base in P. rotundata n. sp.; the more numerous axial ribs (40 vs 26 in P. rotundata n. sp.; the microsculpture of 5-6 threads alternating some thicker and more marked vs groups of 3-4 thin threads separated by microfurrows in P. rotundata 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 848-849, DOI: 10.5252/zoosystema2023v45a25, http://zenodo.org/record/10458066