Geminitor, Hyman & Köhler, 2022

Hyman, Isabel T. & Köhler, Frank, 2022, Homoplasy in shells discombobulated the taxonomy: revision of the larger helicarionid land snails of northern Queensland, Australia (Stylommatophora: Helicarionidae), Journal of Natural History 56 (41 - 44), pp. 1727-1799 : 1757-1758

Geminitor gen. nov.

Type species Pravonitor laura Stanisic, 2010 .

Etymology

From geminus (Latin = twin-born, twin), referring to the double-chambered penis, and Nitor , a helicarionid snail genus; of masculine gender.

Differential diagnosis

External appearance. Shell small to medium-sized (SW 6.6–14.6 mm), pale gold to amber, often paler on the underside, glossy, 4.8–6.3 whorls, discoidal to subdiscoidal with a low to moderately elevated spire; whorls rounded; umbilicus narrow, sealed with a mucous plug; lip slightly reflected over umbilicus. Protoconch with moderately coarse spiral grooves, becoming finer and more crowded on teleoconch. Body colour pale brown to white, often with a grey tail tip and black eyestalks. Mantle lobes small; shell lappets moderately long, triangular, wide at base, tapering to a point. Caudal horn moderately large.

Genital anatomy. Ovotestis embedded in digestive gland. Carrefour visible; talon usually embedded in albumen gland. Spermoviduct not folded. Free oviduct long, with elongate capsular gland; free oviduct internally smooth. Vagina very short. Bursa copulatrix moderately short, inserted on vagina, base of duct usually swollen, then narrowing; bursa elongate. Penis with two chambers, distal chamber with longitudinal pilasters and ridges, upper chamber sculptured with rounded, transverse plates. Verge-like structure sometimes present between penial chambers. Penis tunica attached by muscle fibres to middle of epiphallus; epiphallus enters penis through simple pore or small verge; epiphallus 2 longer than or shorter than epiphallus 1; epiphallus 2 broader than epiphallus 1; epiphallic caecum moderately long to long, penial retractor muscle attached to base of caecum. Long, slender epiphallic flagellum with axial filament present; no internal cryptae visible.

Remarks

Geminitor is introduced for small to medium-sized snails with a relatively pale, unbanded, discoidal to subdiscoidal shell and a two-chambered penis. Two species are removed from Pravonitor ( G. laura , G. villaris ) and three species are described as new ( G. kullaensis , G. wenlockensis , G. macveae ).

Geminitor can be characterised by its small to medium-sized, pale gold to amber, glossy shell, often paler on the underside, with rather coarse microspiral sculpture on the protoconch (becoming finer on the teleoconch). The shell is discoidal to subdiscoidal in shape, with a low to moderately elevated spire and a rounded whorl profile. Anatomically, it is distinguished particularly by its two-chambered penis, often with a beehive-shaped verge leading into the second chamber, and/or a series of overlapping plates around the opening between the two chambers. Other key features include the long, slender reproductive system with visible carrefour, the very short vagina, the broad epiphallus 2 compared to epiphallus 1, the long caecum with basal attachment of the penial retractor muscle, and the long, slender flagellum.

This genus is restricted to Cape York Peninsula, being found from just north of Cairns to Bramwell . This area is under-collected and it is likely that there are additional undescribed species .