Pseudolibera matthieui, Sartori, André F., Gargominy, Olivier & Fontaine, Benoît, 2014

Sartori, André F., Gargominy, Olivier & Fontaine, Benoît, 2014, Radiation and decline of endodontid land snails in Makatea, French Polynesia, Zootaxa 3772 (1), pp. 1-68 : 45

Pseudolibera matthieui sp. nov.

Figures 25 B; 27; 36D; 38E; 39.

Examined material (118 specimens). Holotype: MNHN 26531, Mk13. Paratypes: MNHN 26532, 8 shells, Mk13. Additional material: 1 shell, Mk03; 2 shells, Mk04; 101 shells, Mk13; 1 shell, Mk16; 1 shell, Mk19; 3 shells, Mk22.

Type locality. West coast, approximately 3 km south of Temao, Makatea (15.85189°S; 148.28018°W). Cave. Limestone, alt. 10 m; station Mk13.

Diagnosis. Shell less than 7 mm in diameter, depressed, flammulated; apex depressed to barely raised, spire elevated; peripheral keel narrow; teleoconch sculptured by subequal axial and spiral ribs, not reduced on shell base; palatal wall devoid of barriers; 1 parietal barrier extending 1½ whorls, with a bifurcated mid sector.

Description. Shell depressed, dome-shaped, white, with regularly spaced, amber flammulations on the apical surface, absent or restricted to the peripheral keel on the shell base. Shell wall very thin, opaque to pellucid; periostracum adherent, shiny. Apex depressed to barely raised; spire elevated, latter whorls descending more rapidly. Apical suture impressed at apex, progressively deepening in subsequent whorls; umbilical suture impressed at apex, adpressed approximately from the third whorl onwards. Whorls concave above and below narrow peripheral keel, transitioning into broadly convex toward the apical suture and shell base; junction of basal and columellar walls initially obtusely angled, developing a keel approximately from the sixth whorl onwards. Transition between protoconch and teleoconch indistinct. Protoconch sculptured by relatively broad primary axial ribs, with interspaces 2–3 times their width, overlaid by a fine secondary sculpture of oblique, axial and spiral elements; oblique elements represented by irregular riblets on the first whorl, gradually transitioning into axial riblets with interspaces approximately equal to their width; secondary spiral sculpture of the protoconch composed of fine lirae, with interspaces approximately four times their width, forming tiny nodules at intersections with oblique and axial riblets. Primary ribs of the protoconch gradually transitioning into taller ribs, which comprise the primary axial sculpture of the teleoconch; secondary axial riblets of the protoconch gradually increasing in number and persisting as the secondary axial sculpture of the teleoconch. Spiral sculpture of the protoconch transitioning into wavy spiral ribs of the teleoconch, more closely spaced and slightly lower than the primary axial ribs of the teleoconch; nodular projections present at intersections between spiral and axial ribs. Sculpture not reduced on shell base. Umbilicus rapidly expanding in diameter for approximately the first 3 whorls, remaining constant in diameter for approximately 2 whorls, subsequently constricted by inward growth of the lower columellar wall and lip. Peristome elongated crescent, with rostrate periphery; columellar lip reflected. Palatal wall devoid of barriers. Parietal wall with 1 barrier, positioned slightly closer to the apical than the umbilical suture, descending gradually anteriorly and posteriorly, extending posteriorly for c. 1½ whorls, with a bifurcated tip along its mid sector; onset of bifurcated tip approximately 1/2 to 3/4 whorl behind the aperture; end of bifurcated tip c. 1¼ whorls behind the aperture. Other shell features that can be expressed numerically are shown in Table 3.

Remarks. The bifurcated section of its parietal barrier distinguishes P. matthieui from all other Pseudolibera . However, the Y-shaped sector of the barrier lies deeply within the aperture and is not observable in intact specimens using reflected or transmitted light. The flatter apex of P. matthieui provides the best feature for distinguishing intact specimens from the somewhat similar P. lillianae , P. solemi and P. cookei sp. nov. Additionally, P. matthieui differs from P. lillianae in its deeper sutures, smaller shell size and slightly shorter peripheral keel; from P. solemi in its narrower peripheral keel, more frequent and larger flammulations, and in its usually lower spire; and from P. cookei in its deeper sutures, more crowded and less conspicuous axial sculpture, and in exhibiting spiral sculpture on the shell base.

Examining damaged or carefully dissected shells of P. matthieui , we verified the morphology of the barrier in one shell each from stations Mk04, Mk16, Mk19 and Mk22, and in 23 individuals from the type locality (Mk13). All specimens from the west side of Makatea (stations Mk13 and Mk16) have the first two whorls flat to barely raised, whereas individuals from the east side (stations Mk03, Mk04, Mk19 and Mk22) exhibit a depressed spire for the first four whorls ( Fig. 27 E). Unfortunately, only a few specimens were found on the east coast and all but one are not fully grown, making the significance of the difference in initial growth difficult to assess. Differences in coloration and sculpture between individuals from the west and east sides appear to be minor.

Etymology. This species is dedicated to Matthieu Fontaine, son of the third author.

Figures

FIGURE 25. Holotypes of: A. Pseudolibera solemi sp. nov.; B. P. matthieui sp. nov.; C. P. cookei sp. nov.; D. P. aubertdelaruei sp. nov. Scale bars = 5 mm.

FIGURE 27. Pseudolibera matthieui sp. nov. A – C. Holotype (MNHN 26531), apical views; A. General view; B. Sculpture of the protoconch and early teleoconch; C. Sculpture of the late teleoconch; D. Umbilical view of dissected specimen (station Mk 13), showing the full extent of the bifurcated portion of the parietal barrier; red dashed line indicates the position of the aperture; E. Specimen from station Mk 19, with the first four whorls of the spire depressed; Scale bars: A, D = 2 mm; B, C = 0.4 mm; E = 5 mm.