Plectorhagada teres, Taylor & Johnson & Stankowski, 2015

Taylor, James P. A., Johnson, Michael S. & Stankowski, Sean, 2015, Molecular phylogenetics and complementary geographical distributions of species of the Western Australian land snail genera Plectorhagada Iredale, 1933 and Strepsitaurus Solem, 1997 (Gastropoda: Camaenidae), Zoological Journal of the Linnean Society 174 (2), pp. 305-321 : 316-317

PLECTORHAGADA TERES SP. NOV.

FIGURES 1 , 3 , 5. 6 , 9 , 10 , 11

Type locality

Western Australia, Cape Range (21°59′18.6″S, 113°57′13.1″E)

Material examined

Holotype: WAM S67364 . Paratypes: WAM S67365, S67366 , and S67367 .

Etymology

Latin ‘ teres ’, meaning polished, smooth, referring to the lack of sculpturing on the shell, in contrast with other members of the genus.

Description

Holotype: shell 19.3 mm wide, 15.7 mm high, H / D ratio 0.81, with 4.4 whorls, and fully closed umbilicus. Based on 15 measured adults, shell relatively large, adult diameter 18.54–21.75 mm (mean 19.70 mm, SD 0.96 mm), with 4.125 –4.500 (mean 4.33, SD 0.18) whorls ( Fig. 9 ). Apex and spire moderately and evenly elevated, shell height 14.16–16.94 mm (mean 15.69 mm, SD 0.91 mm), H / D ratio 0.640 –0.870 (mean 0.799, SD 0.075). Body whorl evenly rounded, without trace of angulation, whorls of spire relatively flat. Early spire with very fine pustules. Spire lacking crenulations ( Fig. 10 ). Body whorl descending sharply just behind lip. Palatal and basal lips reflected and narrowly expanded, columellar lip covering most of umbilicus. Umbilicus closed or with a narrow lateral crack. Parietal wall with thin to medium thick callus, its edge not raised. Colour very light yellow above (almost white), lighter on shell base, sometimes with a faint narrow reddish brown spiral supraperipheral band. Based on six dissected adults, genitalia ( Fig. 11 ) with medium to large albumen gland, shortened prostate, about half the length of the uterus. Spermatheca short to medium in length, with a thick shaft. Vagina shorter than penis, widest at the centre. Epiphalus relatively long, tapering into a long slender vas deferens. Epiphalic caecum absent. Large, kidney-shaped penis without accessory ridges. U-pilaster thin, running the length of the penis.

Comparative remarks

Shells of Plectorhagada teres sp. nov. are most similar to those of P. scolythra , its geographically closest congener ( Fig. 9 ). They are slightly larger, but with substantial overlap. The most consistent difference is the lack of crenulations on the upper spire of Plectorhagada teres sp. nov. ( Fig. 10 ). The supraperipheral band is also typically fainter than in P. scolythra . Based on shells alone, however, distinguishing between the two species is difficult. The reproductive system of Plectorhagada teres sp. nov. shares common characteristics with other species of Plectorhagada , including a relatively short prostate, uterus, and vagina, and an epiphalus that tapers into a slender vas deferens. There are, however, some clear differences. Plectorhagada teres sp. nov. can be distinguished from P. scolythra (see Solem, 1997) by the lack of an epiphallic caecum, which is present in P. scolythra , and the absence of accessory ridges on the anterior penial wall, which are greatly enlarged in P. scolythra . The species can be distinguished from P. plectilis based on the size of the albumen gland, which is enormous in P. plectilis and only slightly enlarged in P. teres sp. nov. Also, accessory ridges on the internal penial wall are very small in P. plectilis and are absent in Plectorhagada teres sp. nov. Plectorhagada carcharias has a very similar reproductive system to P. teres sp. nov., but has prominent accessory ridges on the interior penial wall, which are absent in P. teres sp. nov.

Distribution

This species is known only from the periphery of the northern end of Cape Range, from near Mangrove Bay on the west side to near Exmouth on the east side. This distribution spans 19 km, and complements that of P. scolythra , which is on the periphery of Cape Range further south. The gap between the known distributions of the two species is 15 km on the west side and 17 km on the east.

Figures

Figure 1. Sample sites for Plectorhagada and Strepsitaurus. Large map (between North West Cape and Cape Range in the north and Shark Bay in the south) shows sites for Plectorhagada and southernmost sample sites of Strepsitaurus ningaloo (SNA, SNB). The shaded area is the known distribution of Strepsitaurus. The expanded map shows central Cape Range, with the sample sites of Strepsiaurus. Dotted lines indicate recorded distributions of species, based on Solem (1997). Open circles indicate sites for species restricted to gorges on the western side of the Cape Range, the shells of which are shown in the lower right corner. Site codes as described in Table 1.

Figure 3. Maximum-likelihood (ML) tree for Plectorhagada and Strepsitaurus based on concatenated sequences of COI and 16S. Inset shows relationships with the out-groups. Numbers indicate bootstrap support for the ML tree, all of which were less than or equal to the posterior probabilities from the Bayesian analysis.

Figure 5. Scores on the first three principal components for shell morphology in Plectorhagada.

Figure 6. Scores on discriminant functions of shell traits among Plectorhagada carcharias, Plectorhagada scolythra, and Plectorhagada teres sp. nov.

Figure 9. Shells of holotype of Plectorhagada teres sp. nov. (A–C), compared with Plectorhagada scolythra from site PSI (D–F) and Plectorhagada carcharias from site PCD (G–I).

Figure 10. Upper spire of holotype (A) and paratypes (B, site PSB; C, site PSJ) of Plectorhagada teres sp. nov., illustrating its lack of sculpture compared with Plectorhagada scolythra (D, site PSH; E, site PSF) and Plectorhagada carcharias (F, site PCF).

Figure 11. Reproductive system (A) and penial anatomy (B) of Plectorhagada teres sp. nov. Abbreviations: dg, prostate; e, epiphalus caecum; gd, hermaphroditic duct; gg, albumen gland; p, penis; pp, U-shaped pilaster; rm, retractor muscle; s, spermatheca; ut, uterus; uv, oviduct; v, vagina; vd, vas deferens; y, atrium. All notations follow Solem (1997).