Geminitor villaris
Creators: name: Hyman, Isabel T.
name: Köhler, Frank
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Stylommatophora
Helicarionidae
Geminitor
Geminitor villaris

description: Geminitor villaris (Reeve, 1854)
(Figures 4, 6 (b–c), 8(b), 10)
Helix villaris Reeve, 1854: pl. 195, sp. 1375; Pfeiffer 1855: 146; Cox 1864: 15.
Xesta villaris: Cox 1868: 2, pl. 10. fig. 8.
Helix (Thalassia) villaris: Brazier 1876: 118.
Nanina (Macrochlamys) villaris: Pfeiffer 1878 –1881: 44.
Nanina (Subg. Xesta Sect. Macrochlamys) villaris: Tryon 1886: pl. 105, pl. 35, fig. 41.
Pravonitor villaris: Stanisic, 2010: 300–301, 326.
Material examined
Syntypes. NHMUK 1982243, Lizard Is., Qld, Australia, 3 specimens.
Other material. See Table 1.
Diagnosis
External morphology. Shell (Figure 6 (b–c)) small (SW 8.1–10.7 mm), pale gold, 4.8– 5.7 whorls, subdiscoidal with a moderately elevated spire, whorls rounded; umbilicus narrow, sealed; protoconch with moderately coarse spiral grooves, becoming finer and more crowded on teleoconch. Body (Figure 8 (b)) white with grey on dorsal part of tail and tail tip, and black eyestalks (in alcohol). Mantle lobes small; shell lappets triangular, tapering. Caudal horn moderately large.
Genital anatomy. Genitalia (Figure 10) with short, swollen vagina; bursa copulatrix moderately short, duct broad, bursa rounded. Penis large, internally with two chambers, distal portion with thin outer wall and thicker inner wall, sculptured with a few longitudinal ridges, and a single large, ridged longitudinal pilaster with a caecum-like extension; proximal portion sculptured with transverse elongate plates arranged like petals around penial verge; 100% enclosed in penial tunica. Epiphallus enters penis through a small, beehive-shaped verge; epiphallus longer than penis, epiphallus 2 similar in width to penis, gradually narrowing, epiphallus 1 slightly narrower; epiphallus 2 longer than epiphallus 1; long epiphallic caecum present, with basal attachment of the penial retractor muscle; flagellum moderately short, slender, without obvious internal cryptae. Spermatophore simple, consisting of soft capsule and long, slender tail-pipe sculptured with two ridges with indistinct teeth.
Remarks
This species was described as Helix villaris from Lizard Island by Reeve (1854), who noted the delicate, pale-green horny shell of five whorls, with a minute umbilicus and very finely sutured margin. No measurements were given, but the most mature syntype specimen is approximately 10 mm in width. The species was attributed to Pfeiffer (1855) by Reeve and all contemporary authors, but Reeve’s publication precedes Pfeiffer’s and it is now accepted as the original description. Pfeiffer gave the type locality as ‘Cape York, Torres Strait, Lizard Point, Australia’ rather than Lizard Island, and subsequently the species was for some years regarded as coming from much farther north. It was briefly synonymised with Pravonitor kreffti from Cape York (Cox 1868), and was recorded by Brazier (1876) from Cape York and Albany Island following the Chevert Expedition. These records probably refer to the species described herein as Pravonitor septentrionalis.
Iredale (1937) relegated this species to a junior synonym of Expocystis rustica, followed by Smith (1992) and Hyman and Ponder (2010). However, Stanisic et al. (2010) reinstated Helix villaris, placing it in the genus Pravonitor. Herein we have placed this species in new genus Geminitor, based on anatomical characters including the presence of a two-chambered penis, as well as genetic data.
No topotype material exists other than the syntypes, which are merely empty shells. We have examined the available spirit-preserved material and found that it appears to represent four different species. One lot (QM MO23884) we tentatively assigned to G. kullaensis (see Remarks for G. kullaensis below). A second (QM MO20694), referred to above as P. villaris ‘Rifle Creek’, was smaller than the recorded measurement of P. villaris and is found significantly farther south, and is described below as the new species Geminitor macveae sp. nov. The remaining material fell into two categories: multiple lots from around Cooktown (referred to above as P. villaris ‘Cooktown’), contrasting with a single lot from 50 km farther north, from Starcke Station Gate near Mt Webb National Park (P. villaris ‘Starcke’). Both were very similar in external appearance. Their internal anatomy was also very similar, indicating a very close relationship if not conspecificity, but showed some consistent differences when several specimens from each population were compared. The Starcke specimens had a more elongate reproductive system, with a longer and slenderer penis, epiphallus and flagellum (Figure 10 (d–f)). The upper chamber of the penis was much longer, and the penial verge appeared longer and more slender as well. Both species had a single large longitudinal pilaster, folded and wrinkled, but in the Cooktown specimens this was larger and had a caecum-like extension (not attached to the penial wall).
It is not clear whether these differences are sufficient to ensure reproductive isolation. Moreover, without topotype material, and with such a strong similarity between the populations, it is very difficult to determine which should bear the name P. villaris. Therefore, we elect to retain both populations in P. villaris at the present time, with a recommendation for further collecting and genetic studies.
Geminitor villaris is recorded from north of the Bloomfield River to Cape Melville and off-lying islands, in dry vine thicket and adjacent woodland (Stanisic et al. 2010). Our studies can only confirm a smaller range, from Cooktown to Mt Webb National Park (Figure 4). This species is very similar anatomically to its parapatric congener G. laura but differs in its significantly smaller size and paler shell and body colouration. It also has a more distinct, swollen vagina, and differs in the internal anatomy of the penis and its shorter bursa copulatrix and flagellum.
description: Published as part of 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), pp. 1727-1799 in Journal of Natural History 56 (41 - 44) on pages 1762-1765, DOI: 10.1080/00222933.2022.2136017, http://zenodo.org/record/7380681