Tonkinospira depressa ( Jaeckel, 1950 )

Páll-Gergely, Barna, Grego, Jozef, Vermeulen, Jaap J., Reischütz, Alexander, Hunyadi, András & Jochum, Adrienne, 2019, New Tonkinospira Jochum, Slapnik & Páll-Gergely, 2014 species from Laos and Vietnam (Gastropoda: Pulmonata: Hypselostomatidae), Raffles Bulletin of Zoology 67, pp. 517-535 : 527

Tonkinospira depressa ( Jaeckel, 1950)

( Fig. 7 )

Systenostoma depressa Jaeckel, 1950: 15–16 , pl. 1, fig. 1. (type locality: Tonkin [northern Vietnam]).

Aulacospira depressa — Vermeulen et al., 2007: 91.

Tonkinospira depressa — Jochum et al., 2014: 32.

Types examined. 33 paratypes (H = 1.6, D = 2.3, Fig. 7 ) ( SMF 202927 ), Tonkin: Flussgenist (river debris), coll. S.H. Jaeckel ex coll. H. Rolle ; 8 paratypes SMF 63875, Tonkin, Genist, coll. Zilch, ex coll. H. Rolle, ex coll. Jaeckel, 8 December 1949 .

Diagnosis. A large Tonkinospira species with a strongly depressed shell, strongly angled body whorl, dense spiral striation, and a peristome that is more or less adnate to penultimate whorl.

Description. Shell large-sized for the genus; depressed conical with rapidly increasing whorls; body whorl strongly angled, keel not symmetrical, situated above mid line of body whorl, flattened above; keel not very sharp; whorls 3.75–4; suture moderately deep; protoconch consists of 1.25 whorls, roughly rugose and spirally striated; teleoconch with rather regular spiral striation and irregular, rough radial lines; aperture oblique to shell axis from lateral view; aperture ovate-oblong; peristome expanded especially in direction of the columella/umbilicus; aperture more or less adnate to penultimate whorl, but peristome continuous; umbilicus narrow, very slightly covered by peristome.

Differential diagnosis. The most similar species is T. pulverea , which has a narrower umbilicus and a more rounded body whorl.

Remarks. Tonkinospira depressa is most similar to the Philippine members of the genus Aulacospira , and reflects this classification by Vermeulen et al. (2007). The most similar species is Aulacospira hololoma ( Möllendorff, 1887), which has a regularly growing protoconch (tightly spired and projected above the teleoconch in T. depressa ) and bears a columellar tooth (lacks in T. depressa ). Moreover, the Philippine species typically have a prominent subsutural furrow on the body whorl, with the keel situated above the middle line of the body whorl (i.e., the keel is not symmetrical) (see Páll-Gergely et al., 2019). Although the similarity between Tonkinospira and Aulacospira is striking, the true phylogenetic relationships cannot be resolved based on conchological characters only. Tonkinospira depressa further differs from other Tonkinospira species in the brownish shell colour, which is colourless in the other species of this genus.

Figures

Fig. 7. Tonkinospira depressa (Jaeckel, 1950), SMF 202927 (paratype). Scale bar represents 2 mm.