Parashiela Laseron, 1956

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 : 834-836

Genus Parashiela Laseron, 1956

Parashiela Laseron, 1956: 439 .

TYPE SPECIES. — Parashiela ambulata Laseron, 1956: 439 , 479, fig. 145 (type by original designation).

DIAGNOSIS. — Shell of small to minute size for the family, less than 2 mm in length, ovate-conic, nonumbilicate or with narrow umbilical fissure, with axial ribs extending to the base. Fine spiral microsculpture densely and minutely granulated. One to four strong, spiral cords on body whorl, one or two cords on first whorls or total absence of spiral cords on body whorl. Aperture with double peristome, almost circular, lacking anterior or posterior angulations or slightly angled or channels, outer lip orthocline o prosocline, with varix. Protoconch (if multispiral) smooth except for one or two weak spiral thread or (if paucispiral) with irregular spiral ridges.

Head-foot: cephalic tentacles rather short, ciliated, with parallel sides; a short posterior pallial tentacle and a short, narrow metapodial tentacle; long, distinct anterior pedal gland, no posterior pedal gland. Operculum: oval, thin, nucleus eccentric (after Ponder 1985: 59).

REMARKS

The genus Parashiela Laseron, 1956 includes a group of small species from the Indo-Pacific and the Western Atlantic (Carlo Smriglio, pers. comm.). Parashiela is currently represented by three recognised species ( MolluscaBase 2023c), all extant (no fossil specimens recorded so far): P. ambulata Laseron, 1956 , Parashiela invisibilis ( Hedley, 1899) and Parashiela liddelliana ( Hedley, 1907) . A fourth nominal species, Parashiela beetsi Ladd, 1966 , is regarded as a synonym of P. ambulata ( Ekawa 1993; Higo et al. 1999; Hasegawa 2006b). As already suggested by van Gemert (2016: 8) the number of Parashiela species is actually larger. Ponder (1985: 51) reported “an undescribed species” from Madagascar with a paucispiral protoconch with spiral sculpture (MNHN). Criscione et al. (2016: 9, fig. 5) reported a Parashiela sp. from the Society Islands, morphologically similar to, but genetically divergent from a typical P. ambulata from Fiji.

Janssen et al. (2011: 415, pl. 15, fig. 3) and Blatterer & Blatterer (2019: 245, 247, pl. 119, fig. 4a-d) figured a Parashiela sp. from the northern Red Sea. We note that the specimen figured as Parashiela sp. from the northern Red Sea by Blatterer & Blatterer (2019: 245, 247, pl. 119, fig. 5a, b) probably belongs to another genus based on its simple peristome.

Four distinct species of Parashiela from Indonesia, Papua New Guinea and Micronesia are figured in webpages (at https://ingokurtz.jimdofree.com/mollusca-weichtiere/rissoidae/): two have a multispiral protoconch, one with a thin suprasutural spiral cordlet on the teleoconch, the other with a slender teleoconch with narrow base; two have a paucispiral protoconch, one with the apex strongly sculptured by 5 spiral cordlets, the other with the apex sculptured by thin spiral threads and microgranules.

Geiger et al. (2007) figured a specimen morphologically somehow intermediate between P.ambulata and P. invisibilis , with 2 spiral cordlets on the teleoconch.

Middelfart et al. (2020) figured a specimen as Parashiela cf. invisibilis , very similar to P. ambulata (slender shell, chromatic pattern, etc.), but with 3 evident spiral cordlets on the last whorl, as in some forms of P. invisibilis .

Finally, we have examined 2 shells from Cape Verde, Eastern Atlantic (coll.Carlo Smriglio, Roma), very similar to P.ambulata .

The examination of c. 2350 specimens allowed us to identify 6 species of Parashiela in French Polynesia, of which 5 undescribed: Parashiela ambulata Laseron, 1956 , Parashiela expansilabrum n. sp., Parashiela obesula n. sp., Parashiela rimatara n. sp., Parashiela rotundata n. sp., Parashiela soniae n. sp. We provide some comparative remarks on two additional species, P. invisibilis and P. liddelliana .