Sphendone insolita, 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 : 34-36

Taxon classification Animalia Stylommatophora Partulidae

Sphendone insolita sp. n. Figs 2, 3

Holotype.

UF 425857, 7.2600°N, 134.4493°W, collected along trail to German Lighthouse, Ngeruktabel (Uruktapel) Island, Palau, F. Kraus, 24 August 1998.

Paratypes

(n = 76). Palau: Ngeruktabel (Uruktapel) Island: along trail to German Lighthouse, 7.2600°N, 134.4493°W, F. Kraus, 24 August 1998 (UF 271885, 8 alcohol preserved, UF 271886, 16 dry shells); at ruins of Japanese artillery battery, 150 meters, F. G. Thompson, 23 October 1985 (UF 248690, 16 alcohol preserved; UF 248689, 31 dry shells); along mossy wall downhill of compound ruins, J. Starmer, 21 August 1999 (UF 332693, 6 dry shells).

Other material examined.

Palau: Eil Malk (Mecherchar) Island: southeastern peninsula, from hermit crab, F. G. Thompson, 22 October 1985 (UF 249044, 1 dry shell).

Diagnosis.

Large, obese-pupoid shell approximately 18-23 mm in height and 13-15 mm in width, with 4.5-5.1 whorls. Body whorl descends below the penultimate whorl. Protoconch sculptured with growth lines, strongest near the sutures; spiral sculpture lacking or, less commonly, comprising faint and irregular striae. Wavy spiral striae are progressively stronger and more regular on penultimate and body whorls but never become regular and strong. Peristome widely expanded and reflexed, palatal and parietal margins nearly parallel, base evenly rounded. Palatal margin with slight central thickening; parietal margin attaching to the body whorl at umbilicus. Penis long, with apical insertion of the vas deferens and retractor muscle. Approximately ten longitudinal pilasters coalesce to form a ridge that defines a small apical chamber below the insertion of the vas deferens.

Description of holotype.

Shell obese-pupoid, height 22.2 mm, width 14.0 mm, with 4.9 whorls (Fig. 3 A–C). Whorls moderately inflated, with impressed sutures. Apex somewhat bluntly rounded (Fig. 5A). Protoconch and teleoconch whorls sculptured with strong growth lines, especially near the sutures; there are also irregularly expressed, weak and wavy spiral striae that become progressively stronger in later whorls. Last whorl descending underneath the penultimate whorl. Aperture elongate, sides nearly straight and parallel. Outer edge of peristome curving slightly inward at middle, base evenly rounded. Aperture height 12.1 mm, width 9.3 mm. Interior of aperture brown. Peristome nearly complete, broadly expanded and reflexed, thickened, brown towards the aperture, fading to brown-white and reflexed abaperturally. Parietal callus thin in the middle and much thickened at the inner and outer insertions of the lip. Shell color medium brown, with a poorly defined paler band below the suture on early whorls that widens on subsequent whorls. Penultimate whorl pale brown to straw yellow-brown except for a poorly defined and narrow darker-brown band below the suture. Body whorl darkens, the second half entirely darker brown.

Variation. Measurements of 56 adult shells: height 18.3-22.7 mm, mean 21.1 ± 0.8 mm; width 12.9-14.9 mm, mean 14.0 ± 0.4 mm; whorls 4.5-5.1, mean 4.9 ± 0.1. Aperture height 10.5-12.1 mm, mean 11.3 ± 0.4 mm. Aperture width 8.4-9.8 mm, mean 9.2 ± 0.3 mm. Most shells are similar to the holotype in coloration, but three of 79 shells are uniformly white. These white-shelled individuals have normal surface sculpture and are not worn. Nor are they albino, as evidenced by their normal mantle pigmentation. Most shells are dextral, but two of 79 are sinistral.

Pallial system (2 specimens). Nephridium nearly 2/3 length of pallial cavity, broad at base, tapering anteriorly, and sharply turned at renal orifice (Fig. 2). Pericardium approximately 1/3 length of nephridium. Pulmonary vein long and unbranched, ending near mantle collar. Mantle lacks any other obvious venation.

Radula (2 specimens). Central tooth two-thirds height of lateral teeth, trigonal, with poorly defined ectocones (Fig. 3I, central row). First lateral teeth bicuspid, ectocone 1/3-1/2 height of broad mesocone, which narrows abruptly at the tip (Fig. 3I, flanking central row). First ten lateral teeth similar in size and shape. Next five rapidly becoming narrower and beginning to develop multiple ectocones (Fig. 3H). Next 80 teeth narrow, slowly grading into marginals, width approximately one-quarter height, with two to several ectocones (Fig. 3G).

Jaw (1 specimen). Crescent-shaped, thin, stegognathous, composed of many narrow flat plaits that converge towards middle of cutting edge, which is not raised and does not bear a central cusp (Fig. 3F).

Reproductive system (10 specimens). Prostate gland short, extending only a short distance beyond albumen gland (Fig. 3D). Vas deferens weakly attached by fibers above penial-oviduct juncture, attached strongly to penis at its mid-point and again to penial-retractor muscle just above insertion on apex of penis; entering penis apically. Penis relatively long, cylindrical, divided into two chambers; the main chamber sculptured with numerous longitudinal pilasters crossed perpendicularly by weaker pilasters; the apical chamber sculptured with relatively weak pilasters. Pilasters fuse at the junction of the two chambers, forming a ridge below the insertion of the vas deferens (Fig. 3E). Atrium very short. Vagina short. Bursa copulatrix receptical oblong, tapering gently and imperceptibly to its duct. Single large egg 6.4-6.6 mm, mean 6.5 ± 0.1 mm (n = 6), with hard calcareous shell (Fig. 3D) found in six of ten dissections, one of these also had an embryo; another embryo found in an individual without an egg. Hermaphroditic duct narrow and highly convoluted.

Comparisons with other species.

The new species differs from other partulids as stated for the genus.

Etymology.

The trivial name is a feminine Latin adjective meaning unusual, in recognition of both the unusual shell shape and ecological habits for a partulid.

Distribution.

Known only from southeasternmost Ngeruktabel (Uruktapel) and nearby Mecherchar (Eil Malk) Islands, Palau, Caroline Islands (Figs 7, 9). These two islands are separated by shallow waters and were connected in the past few thousand years, as the maximum depth between the two islands is only 25 m ( Defense Mapping Agency 1996). Because all the hundreds of islands within the central fringing reef of Palau comprised a single island during the last glaciation event ( Colin 2009), the species may be more widely distributed among other of the Rock Islands than is currently apparent.

Ecological notes.

Live individuals of the new species were collected only from beneath rocks, between soil and the overlying rock, or deep in rock piles. Dead shells were also found on the soil surface and in leaf litter among stones. The site is well-developed limestone rainforest (Fig. 10) that was partially cleared during WWII but is now difficult to distinguish from undisturbed forest ( Crombie and Pregill 1999).