Australdonta pakalolo, Sartori, André F., Gargominy, Olivier & Fontaine, Benoît, 2013

Sartori, André F., Gargominy, Olivier & Fontaine, Benoît, 2013, Anthropogenic extinction of Pacific land snails: A case study of Rurutu, French Polynesia, with description of eight new species of endodontids (Pulmonata), Zootaxa 3640 (3), pp. 343-372 : 359-361

Australdonta pakalolo sp. nov.

Figures 8 , 9 , 14 F, 15A

Examined material (2 specimens). Holotype: MNHN 25195, Rr2. Paratypes: MNHN 25196, 1 shell, Rr35.

Diagnosis: Shell light fawn, without flammulations; supraperipheral groove lacking or very shallow, developping from the fourth whorl onwards; primary and secondary axial sculpture of the teleoconch little differentiated; periphery angled; apertural barriers represented by traces (three to five parietals, zero to two palatals).

Description: Shell depressed to subdepressed, light fawn, without markings. Shell thin, opaque; periostracum adherent, shiny. Apex barely raised; spire barely to somewhat elevated; later whorls descending more rapidly. Apical suture impressed to canaliculate, umbilical suture impressed. Periphery weakly angled to acutely rounded; very shallow supraperipheral groove, when present, developing from the fourth whorl onwards. Transition between protoconch and teleoconch indistinct. Protoconch sculptured by fine, spiral and axial lirae; spiral lirae less prominent, fading on the transitional zone between protoconch and teleoconch. Axial lirae gradually transitioning into coarser, more crowded riblets, with interspaces two to four times their width, comprising the secondary axial sculpture of the teleoconch; primary axial sculpture of the teleoconch consisting of well spaced ribs, only slightly taller and wider than the secondary riblets, with interspaces approximately ten to twelve times their width.

Umbilicus wide to very wide, moderately to very deep. Peristome ovate to trigonal-ovate. Palatal wall with or without two basal traces, slightly recessed within aperture, extending approximately one-eighth whorl, similar in prominence and width. Parietal barriers represented by three to five traces; first trace extending approximately onequarter whorl or inwards beyond the line of vision from the peristome; all other traces extending inwards beyond the line of vision from the peristome; all but the fourth trace not recessed within aperture; fourth trace, when present, slightly recessed, much lower than remainder; first trace more prominent than the remainder; second trace, when present, equidistant from first and third traces; second, third and fifth traces similar in prominence and width. Other shell features that can be expressed numerically are shown in Table 2 .

Remarks: Only two specimens of A. pakalolo were recovered from distinct matos, and these display a number of morphological differences. The holotype has a barely elevated spire, a very shallow supraperipheral groove, weakly angled periphery, very wide umbilicus, palatal wall devoid of apertural barriers, and five barrier traces on the parietal wall. Conversely, the paratype is a relatively high shell, without supraperipheral groove, a trigonal outer wall, narrower umbilicus, two palatal and only three parietal traces. Additionally, the holotype appears to display a higher expansion rate of its helicocone, resulting in a larger aperture, and a slightly larger body size. Due to these differences we initially considered these specimens as representing two separate species. However, similarities in shell sculpture and in the morphology of the parietal barriers, as well as a reluctance to describe two species based on single specimens, led us to lump these shells under one highly variable species. They are, after all, more similar to one another than to any other known endodontid species. A critic re-evaluation of this hypothesis when more material surfaces is, of course, desirable.

The holotype of A. pakalolo shares with A. oheatora a very shallow supraperipheral groove and an ovate peristome constricted only by parietal traces. However, specimens of A. oheatora are much higher, have a deeper sulcus, a narrower umbilicus, a canaliculate, deeper apical suture, and display heavier axial sculpture with clearly distinguished primary ribs and secondary riblets. Reduced apertural barriers are also features of A. radiella (Pfeiffer, 1846) and A. radiella rurutuensis (Garrett, 1879) , but these species differ from A. pakalolo in having a more rounded periphery, well-marked spiral striae on the teleoconch, sharply defined and much stronger axial sculpture, as well as regularly spaced flammulations, which persist even on eroded shells.

Etymology: Pakalolo is the Polynesian name for Cannabis sativa ; the holotype was found on the ground of a plantation of this psychotic plant, hidden within the karstic, secluded mato. It is treated as a noun in apposition.

Figures

FIGURE 8. Australdonta pakalolo sp. nov. A. Holotype; B. Paratype. Scale bars = 1 mm.

FIGURE 9. Australdonta pakalolo sp. nov. Apical views of the holotype (A – C) and paratype (D – F). A and D. General view; B and E. Sculpture of the protoconch and early teleoconch; C and F. Sculpture of the late teleoconch. Scale bars: A, D = 800 µm; B, C, E, F = 200 µm.

FIGURE 14. Apertural view of the holotypes of the new species described herein, illustrated at the same scale: A. Australdonta oheatora sp. nov.; B. A. anneae sp. nov.; C. A. sibleti sp. nov.; D. A. florencei sp. nov.; E. A. teaae sp. nov.; F. A. pakalolo sp. nov.; G. Minidonta boucheti sp. nov.; H. M. bieleri sp. nov. Scale bar = 1 mm.