Pseudostreptaxis harli Pall-Gergely & Schilthuizen

Pall-Gergely, Barna, Schilthuizen, Menno, Oerstan, Aydin & Auffenberg, Kurt, 2019, A review of Aulacospira Moellendorff, 1890 and Pseudostreptaxis Moellendorff, 1890 in the Philippines (Gastropoda, Pupilloidea, Hypselostomatidae), ZooKeys 842, pp. 67-83 : 76-79

Pseudostreptaxis harli Pall-Gergely & Schilthuizen sp. n. Figures 4 B–E, 5B

Type material.

Palawan Province, El Nido Municipality, Shimizu Island, Panaustard (?) leg. J Harl, 15 Feb 2009, NHMW 113033 (holotype); same data, NHMW 113034/3 photographed paratypes (Fig. 4 C–E), HNHM 103477/5 paratypes; PGB/10 paratypes, SMF 351762/3 paratypes; REI/43 paratypes; Palawan Province, El Nido Municipality, Miniloc Island, 11.146N, 119.313E, sieved from litter under neath limestone cliff, leg. M Schilthuizen, 18 Mar 2018, TxEx-PA0003-45, RMNH.MOL.340315/30 paratypes, PGB/60 paratypes.

Diagnosis.

Shell globular, protoconch spirally striated, teleoconch roughly wrinkled and spirally striated; aperture with a single parietal tooth that sometimes consists of two tubercles; aperture adnate to penultimate whorl.

Description.

Shell globular (0.95-1.15 times as wide as high) with bulging whorls and deep suture; in some specimens penultimate whorl narrowed, somewhat similarly to that of Pseudostreptaxis azpeitiae ; colour light brownish-greyish to dark purple; entire shell consists of 4-4.5 whorls; protoconch consisting of ca. 1.25 whorl, finely granulose and spirally striated; teleoconch finely granulose, with some fine, irregular wrinkles and with dense, hardly visible spiral striation; aperture oblique to shell axis, aperture rounded; peristome thickened and expanded, especially in the basal and columellar direction; parietal callus weak, appears as a lime layer on the penultimate whorl; parietal tooth (lamella) elevated, deeply situated, relatively long, in some specimens consisting of two tubercles, which might indicate that it is homologous with the parieto-angular lamella; no other apertural barriers present; umbilicus open but very narrow, showing only the last whorl, mostly covered by expanded peristome.

Measurements (in mm).

H = 2.6-3.0, D = 2.9-3.1 (n = 2).

Differential diagnosis.

Pseudostreptaxis azpeitiae has a keeled penultimate whorl resulting in a shell shape reminiscent of the Streptaxidae . Moreover, the new species has a single parietal tooth, while Pseudostreptaxis azpeitiae possesses 4-5 apertural barriers.

Remarks on shell shape.

This new species is placed in Pseudostreptaxis because of the rounded body whorl, which is keeled in Aulacospira .

The shell of P. harli sp. n. is unusually “spherical”. To obtain a uniform linear distribution, the shell shape may be expressed as the angle obtained by taking the inverse tangent of the ratio D/H ( Örstan 2018). The distribution of the shell shape angles (ε) thus obtained against the mean greater shell dimensions (GSD, the larger of the shell height or diameter) for 2134 pulmonate genera (Fig. 6) forms one major cluster of flat (ε> 50°) shells and at least three smaller clusters of tall (ε <40°) shells. In addition, there is a diffuse cluster of approximately 30 roughly equiaxial and small genera within the approximate ranges of ε = 44°-49° and GSD = 1.5-5 mm (Fig. 6, arrow). The mean shell values (ε = 46°, GSD = 3.03 mm) for Pseudostreptaxis harli sp. n. place this species in the latter cluster. The genera in this cluster, being members of eight families, form a phylogenetically diverse group. The evolutionary convergence of these small genera on a similar shell shape suggests that they and any individual species that may be included in this cluster, including P. harli sp. n., share a unique biological trait that has enabled them to overcome the opposing selective forces that have prevented more species to evolve equiaxial shell shapes.

Distribution.

This species is known from two adjacent tiny islands (Miniloc and Shimizu) on the northeastern coast of Palawan (Fig. 2).

Etymology.

This new species is named after Josef Harl, a friend of the first author, who first collected this new species and provided it for study.