Sphendone, Slapcinsky, John & Kraus, Fred, 2016

Slapcinsky, John & Kraus, Fred, 2016, Revision of Partulidae (Gastropoda, Stylommatophora) of Palau, with description of a new genus for an unusual ground-dwelling species, ZooKeys 614, pp. 27-49 : 33-34

Taxon classification Animalia Stylommatophora Partulidae

Genus Sphendone gen. n.

Type species.

Sphendone insolita sp. n.

Content.

One species, Sphendone insolita sp. n.

Diagnosis.

Shell obese-pupoid (Fig. 3B), protoconch sculptured with growth lines, strongest near the apical suture (Fig. 5A); spiral sculpture absent or consisting of very weak and inconsistent striae. Wavy spiral striae become progressively stronger and clearer on the penultimate and body whorls. The final half of the body whorl does not extend beyond the penultimate whorl (Fig. 3 A–B). Peristome widely expanded and reflexed, palatal and parietal margins nearly parallel, base evenly rounded. Palatal margin with slight central thickening; parietal margin attaching to body whorl at level of umbilicus. Penis relatively long and narrow, sculptured with approximately 10 longitudinal pilasters that coalesce to form a ridge between the penis and a very short and thin-walled apical chamber with about 10 thin and widely spaced pilasters. The vas deferens and penial-retractor muscle enter at the penis apex. Oviduct usually contains only one (sometimes two) eggs or embryos.

Comparisons with other genera.

The shells of Eua , Samoana , Palaopartula , and Partula are not pupoid in shape; they are attenuated apically. The protoconch of the new species lacks strong spiral striae or pitting, unlike the strong striae of Eua , or the pitted striae of Palaopartula , Partula , and Samoana . Sphendone is similar only to Eua in the apical insertion of the vas deferens into the penis, unlike the lateral insertion into the apical chamber in Samoana , Palaopartula , and Partula (Figure 6). However, Sphendone shares an elongate, two-chambered penis with Samoana , Palaopartula , and Partula that is distinctly different from the short, broad penis with a single chamber found in Eua . The apical chamber of Sphendone is very short, unlike Samoana , Palaopartula , and Partula , which have large apical chambers (Fig. 6). The interior of the penis in Sphendone is sculptured with approximately ten longitudinal pilasters, unlike the single fleshy pilaster of Eua or the two large pilasters in the main chamber of the penis of Samoana ( Kondo 1955). The pilasters of the main and apical chambers coalesce, forming a ridge between the two chambers similar to that seen in Palaopartula and unlike that in Samoana and Partula . The penial-retractor muscle enters apically and does not branch, whereas Samoana has a retractor muscle with a secondary branch that attaches to the penial chamber.

Remarks.

A comparison of a partial COI sequence (540 bp) of Sphendone (UF 271885) with sequences from all other partulid genera (655 bp) shows the new genus is well differentiated from other partulid genera (Fig. 8) although we are unable to determine its sister-taxon relationships from an unrooted network.

Etymology.

Sphendone is a feminine Greek noun for a sling missile and is used here in reference to the unique bullet shape of the shell among partulids. The accent is on the first syllable.

Distribution.

Known only from Palau.