Palaopartula Pilsbry, 1909

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 : 31-33

Taxon classification Animalia Stylommatophora Partulidae

Genus Palaopartula Pilsbry, 1909

Palaopartula Pilsbry, 1909, in Pilsbry 1909-1910, pages 166, 306.

Palaeopartula Richardson, 1990, page 6 [incorrect subsequent spelling].

Palaopartula Schileyko, 1999, page 271, figure 327.

Type species.

Partula thetis Semper, 1865; by original designation.

Content.

Partula calypso , Partula leucothoe , and Partula thetis , all Semper 1865.

Distribution.

Known only from Palau.

Diagnosis.

Shell large, elongate, with a tall, relatively flat-sided and acutely pointed spire (Fig. 4). Protoconch small, early teleoconch whorls descend rapidly, remaining tightly coiled and narrow. Aperture elongate, with a greatly expanded peristome, its palatal and parietal sides nearly parallel, palatal edge with a slight central thickening, base rounded, parietal edge joining high on the body whorl. Umbilicus very deep and not covered by the parietal callus. Penis long and narrow, divided nearly equally between a main chamber with strong pilasters running its length that are crossed by weaker pilasters and an apical chamber with narrow pilasters or pustules ( Kondo 1955, figs 118-123).

Comparisons with other genera.

Palaopartula has historically been grouped with Partula . It differs from Partula , Eua , and Samoana in having a relatively large and more elongate shell with a high and rapidly descending spire (Fig. 5 B–D). In contrast, Partula (Fig. 5 G–H), Eua (Fig. 5E), and Samoana (Fig. 5F) have relatively blunt apices, with rounded whorls that expand relatively rapidly and descend slowly. The height/width ratio range of the three Palaopartula species is 2.0-2.3, versus 1.5-1.9 for the Partula , Eua and Samoana species listed in Appendix 1. The early teleoconch whorls of Palaopartula are variable in sculpture: Palaopartula calypso (Fig. 5B) and Palaopartula leucothoe (Fig. 5C) have pitted spiral striae like most Partula and Samoana , although the spiral striae are much weaker; Palaopartula thetis (Fig. 5D) is unlike any other partulid in being sculptured with raised axial and spiral sculpture that join to form nodules. The peristome of Palaopartula species is more widely reflected than in any other genus of Partulidae , and the parietal edge attaches to the shell higher on the body whorl and does not obstruct the umbilicus, making the umbilicus look particularly deep. Palaopartula differs from Eua in having a long thin penis (Fig. 6D), unlike the short broad penis of Eua (Fig. 6A). Internally the penis of Palaopartula is divided into two chambers, a main penial chamber and an apical chamber, each with 5-15 longitudinal pilasters; this contrasts with Eua , which has only one chamber with one large fleshy pilaster ( Kondo 1955). The vas deferens of Palaopartula joins the apical chamber laterally rather than joining the penial chamber apically, as in Eua . The penial and apical chambers of Palaopartula are similar in width and length and both contain 5-15 longitudinal pilasters, whereas the penial chamber of Samoana is short and bulbous with only two large pilasters that fuse to form a V (Fig. 6B), and the apical chamber is long and narrow and contains 5-10 longitudinal rows of nodules. Palaopartula has an unbranched penial retractor muscle that attaches apically as opposed to the retractor muscle of Samoana which also has a secondary branch that attaches to the penial chamber (Fig. 6B). Palaopartula differs from Partula in having a narrow and usually tapering penis, whereas Partula has a more variable penis that is usually apically inflated and strongly curved ( Kondo 1955). In Palaopartula , the pilasters in both chambers fuse to form a ridge between the chambers, unlike Partula , which has pilasters that do not fuse to form a ridge between the two chambers (Fig. 6E). The vas deferens of Palaopartula remains narrow for its entire length whereas the vas deferens of Partula broadens before entering the apical chamber. Molecular data also do not support placement of Palaopartula within Partula ( Lee et al. 2014) but link it instead with Samoana , from which it differs radically in shell and genital morphology. Accordingly, we here resurrect Palaopartula .

Remarks.

This genus is isolated to the west of all previously named partulid genera (Fig. 7). The species are arboreal, with Palaopartula thetis typically being found in Pandanus leaf axils (FK, pers. obs.). Judging by genetic distances, Palaopartula is distantly related to Partula but clusters more closely to the other partulid genera (Fig. 8), although we are unable to polarize this network to determine directionality of evolution.