Parashiela invisibilis ( Hedley, 1899 )

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 : 836-837

Parashiela invisibilis ( Hedley, 1899)

( Figs 22 ; 50 )

Rissoa invisibilis Hedley, 1899: 418 , fig. 9.

TYPE MATERIAL. — Holotype. Tuvalu Islands • dd; Funafuti Atoll ; 8°31’1”S, 179°13’1”E; 1896; C. Hedley leg., Royal Society Coral Boring Expedition; AMS-C.5892 .

TYPE LOCALITY. — Tuvalu Islands: Funafuti Atoll.

DISTRIBUTION. — Tropical Pacific ranging from the Philippines to southern Japan and to Hawaii (van Gemert 2016: 7) ( Fig. 50 ).

DIAGNOSIS. — Parashiela small for the genus, height 1.20 mm (holotype), ovate-conic. Protoconch paucispiral. Teleoconch with thin orthocline axial ribs, reaching the base and entering the narrow umbilical fissure; four thin spiral cordlets on the last whorl, 2 above the aperture and on upper whorls. Peristome duplicated, with thick and broad varix crossed by evident growth striae. Colouration uniform white.

REMARKS

We note that the holotype has two (not one as originally described: Hedley 1899: 418; van Gemert 2016: 7) very thin spiral cordlets above the aperture and on upper whorls.

We suspect that several of the specimens reported in the literature as P. invisibilis (e.g. Ekawa 1993: 80, pl. 2, fig. 14; Hasegawa 2000:150, pl. 75, fig. 12 [two images]; Hasegawa 2006b: 108, fig. 6; Poppe & Tagaro 2011: pl. 1306, fig. 3; Middelfart et al. 2020: 26, fig. 4A, as Parashiela cf. invisibilis ; but also by Severns 2011: 116, pl. 42, figs 1, 2, as Parashiela sp. and Parashiela beetsi ), which are larger and with more marked spiral and axial sculptures, may actually belong to one or more distinct and probably undescribed species.

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

Figures

FIG. 22. — Parashiela invisibilis (Hedley, 1899): A, B, holotype, height 1.2 mm, width 0.72 mm, Tuvalu Islands, Funafuti Atoll, AMS-C.5892 (Images: A. C. Miller, Copyright: Australian Museum); C, original drawing.

FIG. 50. — Type localities of Parashiela invisibilis (Hedley,1899) (Funafuti Atoll: ○), Parashiela liddelliana (Hedley,1907) (Mast Head Reef:●), Parashiela ambulata Laseron, 1956 (Michaelmas Cay: ✩), and Parashiela beetsi Ladd, 1966 (Eniwetok Atoll: *).