Australdonta sibleti, 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 : 354-358

Australdonta sibleti sp. nov.

Figures 3 C, 6, 14C, 15C

Examined material (139 specimens). Holotype: MNHN 25201, Rr8. Paratypes: MNHN 25202, 8 shells, Rr8. Additional material: 1 shell, Rr6; 1 shell, Rr20; 1 shell, Rr22; 32 shells, Rr31; 26 shells, Rr35; 7 shells, Rr36; 1 shell, Rr38; 11 shells, Rr42; 2 shells, Rr43; 1 shell, Rr53; 2 shells, Rr54; 2 shells, Rr57; 8 shells, Rr62; 32 shells, Rr66; 3 shells, Rr68.

Diagnosis: Shell with a flat apex and spire, rounded periphery, well-spaced primary axial ribs, without flammulations; teleoconch without spiral sculpture.

Description: Shell discoidal, white to light fawn, without markings. Shell thin, usually pellucid, rarely opaque; periostracum adherent, shiny. Apex and spire flat; last whorl descending more rapidly. Apical and umbilical sutures impressed; whorls rounded, periphery rounded to very weakly angled. Transition between protoconch and teleoconch indistinct. Protoconch sculptured by very fine, widely spaced spiral and axial lirae, forming a reticulated pattern; spiral lirae wobbly in aspect, fading on the transitional zone between protoconch and teleoconch. Axial lirae progressively transitioning into coarser ribs, constituting the primary sculpture of the teleoconch. Interspaces between primary ribs occupied by secondary sculpture of two to six wavy axial riblets. Umbilicus very wide, shallow. Peristome crescent-shaped. Palatal wall with two to four recessed traces, all usually very low, rarely with the second and third reaching the prominence of typical barriers; palatal traces/barriers extending approximately one-eighth whorl, with gradual anterior and posterior descension; first columellar in position, often lacking, slightly less prominent and a little more deeply recessed than second; second basal in position, slightly wider than the third, infraperipheral trace; forth often lacking, supraperipheral, a little more deeply recessed, slightly less prominent than third. Parietal barriers two to three in number, not recessed within aperture, extending inwards beyond the line of vision from the peristome, with gradual anterior descension; first and second higher posteriorly, invariably present; third often lacking, less prominent than remainder, approximately constant in height throughout its visible extent. Rarely with a trace between the second and third parietal barriers. Other shell features that can be expressed numerically are shown in Table 2 .

Remarks: Endodontids commonly display flaking periostracal extensions of their shell sculpture (Solem 1976, p. 34). In A. raivavaeana Solem, 1976 (Solem 1976, fig. 23), periostracal lamellae project from the apexes of narrow shell ribs and riblets that closely resemble those of A. sibleti . However, periostracal extensions were not visible in scanning electron micrographs of any of the new species described herein. Given the similarity of the sculptural elements formed by the shell wall, it seems likely that A. sibleti , A. florencei and perhaps a few other of the new taxa established here may have displayed periostracal lamellae, which were not preserved in the dead shells available for examination.

In size, overall shape and coloration, A. sibleti most closely resembles A. pseudplanulata Solem, 1976 , with which it occurs sympatrically. However, the more spaced primary axial sculpture of A. sibleti readily and consistently distinguish it from A. pseudplanulata , even in juvenile material. Additionally, A. sibleti normally has palatal barriers that are much smaller and fewer than the four prominent palatal barriers of A. pseudplanulata . In A. sibleti , this latter arrangement was only found in specimens collected along the Northwest coast of Rurutu (stations Rr42, Rr43 and Rr57), and in one specimen from station Rr31, in the central East coast ( Fig. 6 E). Shell sculpture also seems to display some degree of geographical variation, with all A. sibleti collected in the Southwest of the island (station Rr62) and many collected in the most southern stations exhibiting weaker primary axial ribs. Variation in parietals was essentially in the number of barriers present, with one quarter of the examined material lacking the third barrier, and two specimens showing a trace between the second and third barriers. In other aspects all of these specimens agree well with typical A. sibleti ; variations in shell sculpture and morphology of apertural barriers are thus presently regarded as intraspecific.

Superficially A. sibleti may also be mistaken for A. florencei —which displays a similar primary axial sculpture of well-spaced, narrow ribs—but that species lacks secondary axial sculpture in the late teleoconch, has prominent spiral ornamentation, a narrower umbilicus, a more elevated spire and axial ribs that are slightly denser and taller than those of A. sibleti .

Etymology: This species is dedicated to Jean-Philippe Siblet, head of the Natural Heritage Service of MNHN, eminent birder—nobody’s perfect.

Figures

FIGURE 3. Holotypes of: A. Australdonta oheatora sp. nov.; B. A. anneae sp. nov.; C. A. sibleti sp. nov.; D. A. florencei sp. nov. Scale bars = 1 mm.

FIGURE 6. Australdonta sibleti sp. nov. A – C. Holotype (MNHN 25201), apical views; A. General view; B. Sculpture of the protoconch and early teleoconch; C. Sculpture of the late teleoconch; D. Paratype 6 (MNHN 25202), detail of the peristome; E. Specimen collected at station Rr 42, showing prominent palatal barriers. Scale bars: A, E = 1 mm; B – D = 200 µm.