Partula lutaensis, Sischo & Hadfield, 2021

Sischo, David R. & Hadfield, Michael G., 2021, The tree snail on Rota Island, Northern Mariana Islands, long identified as Partula gibba (Partulidae), is a different species, ZooKeys 1037, pp. 105-118 : 105

Partula lutaensis sp. nov.

Type material.

Holotype. Bishop Museum BPBM 284888 Fig. 3 . Entire specimen collected by Jill Liske-Clark, 20/11/2014 from type locality. Paratypes. BPBM 284889, 2 specimens collected by Jill Liske-Clark, 20/11/2014, from type locality, and BPBM 284890, 3 specimens collected by Jill Liske-Clark, same date, from a second location on Rota Island, Commonwealth of the Northern Mariana Islands.

Type locality.

Rota Island, Commonwealth of the Northern Mariana Islands (CNMI).

Diagnosis.

Shell. Shell dextral, moderately thin, ovate-conic, slightly perforate; umbilicus open; whorls moderately convex, suture adpressed; aperture ovate-elongate, slightly oblique; outer lip reflexed, thick, glossy; parietal lip glossy with light or dark coloration; color of embryonic whorls and post-embryonic whorls variable from shades of brown, buff, white and yellow with prominent white subsutural band; Measurements (N = 48 specimens from five lots in BPBM collections from Rota): height (= length) 15.98 mm, s.d. 0.75 mm; width, 10.64 mm, s.d., 0.24 mm. See Figure 4 for examples of shell color variation. Shell greatly resembles those of Partula gibba on Guam and Saipan ( Crampton 1925).

Distinguishing shells of P. lutaensis from those of P. langfordi .

Shell length of P. langfordi (M = 13.83 mm, s.d. = 0.37 mm, N = 47) was significantly shorter than the length of P. lutaensis sp. nov. (M = 15.98 mm, s.d. = 0.75 mm, N = 48), t(82) = -13.91, P <0.001. Similarly, shell width of P. langfordi (M = 9.74 mm, s.d = 0.36 mm) was significantly less than that of P. lutaensis sp. nov. (M = 10.64 mm, s.d = 0.24 mm), t(90) = -8.02, P <0.001 (Fig. 5 ).

Male reproductive system.

The male reproductive system of Partula gibba figured by Kondo (1955, 1970) and Gerlach (2016) is highly variable. In specimens we examined (Fig. 6A ), the vas deferens entered the penis very near its top, leaving the upper portion of the penis, attached to the retractor muscle and called the caecum by Gerlach (2016), to be very short. In specimens of P. radiolata , the entry of the vas deferens was about 1/5 to 1/4 of the length of the penis below the retractor-muscle attachment (Fig. 6B ). However, the male duct was distinctive in P. lutaensis sp. nov. by the bulge or shoulder at the top of an expanded caecum, proximal to the vas deferens. In the male system of P. lutaensis sp. nov., the attachment of the vas deferens was consistently more distal than in either P. gibba or P. radiolata (Fig. 6C ); the insertion was close to 1/3 of the length of the penis below the retractor-muscle attachment. In no other regard were there any distinctive differences among the penial structures of these three species. The lower attachment of the vas deferens to the retractor muscle in both P. lutaensis sp. nov. and P. radiolata is concordant with their placement as sister taxa in phylogenetic reconstructions of the group. Kondo (1970) found no differences between the male reproductive tract of P. langfordi and P. gibba . We include a modified version of his drawing with ours for comparison (Fig. 6D ).

Ecology.

Type and paratype specimens were found on Epiprenmum aureum and Tectaria crenata (J. Liske-Clark, Northern Mariana Department of Fish and Wildlife, personal communication).

Etymology.

The specific epithet Partula lutaensis recognizes Luta, the indigenous Chamorro name for the island of Rota.

Figures

Figure 3. Shell holotype of P. lutaensis sp. nov.

Figure 4. Left - Color morphs of Partula lutaensis sp. nov. found within a 10 x 10 - meter quadrat. Right - Closeup of a Partula lutaensis sp. nov. with a dark shell.

Figure 5. Scattergram of Bishop Museum shell measurements comparing shell width (y-axis) by shell length (x-axis) of 48 P. langfordi from Aguigan and 47 P. lutaensis sp. nov. from Rota. The mean shell length and width plus standard deviation of each species are encircled. All shells were lipped indicating snails were mature and had reached terminal growth.

Figure 6. Outline drawings comparing the male reproductive tracks of four extant Partula species from the Mariana Islands. Male anatomy abbreviations are as follows: retractor muscle (RM), caecum (C), penis (P), vas deferens (VD), uterus (U). The figure of Partula langfordi is adapted from figure 5 of Kondo (1970). Note, Kondo found no difference between the male reproductive tracts of P. gibba and P. langfordi.