Pseudosubulina nouraguensis, Gargominy & Muratov, 2012

Gargominy, Olivier & Muratov, Igor V., 2012, New taxa of land snails from French Guiana, Zoosystema 34 (4), pp. 783-792 : 789-790

Pseudosubulina nouraguensis n. sp. ( Fig. 5 )

TYPE MATERIAL. — Holotype: French Guiana, Réserve naturelle des Nouragues, Nouragues field station (c. 4°05’N, 52°41’W; K10 square), 85 m a.s.l., T. E. J. Ripken & O. Gargominy, 20.XI.1997, leaf litter on lateritic soil in a natural forest gap ( INVMAR21054 ), MNHN 25073 . Paratypes: same data as holotype, 2 specimens, MNHN 25074 .

TYPE LOCALITY. — Nouragues field station (c. 4°05’N, 52°41’W), Réserve naturelle des Nouragues, French Guiana.

ETYMOLOGY. — The name of the species relates to its type locality.

DIAGNOSIS. — Shell not umbilicate, slender, turrited with straight outline and obtuse apex; consists of up to 10 tightly coiled, slightly shouldered whorls with a deep straight crenulated suture. Protoconch glossy with faint radial and spiral sculpture. First whorl of teleoconch with well-defined radial ribs about same width as intercostal spaces.Surface of later teleoconch whorls with well-defined broad radial ribs much wider than intercostal spaces and with extremely faint, uneven and wavy spiral sculpture. Apertural dentition consists of columellar and basal lamellae and palatal tubercule, repeated half whorl from the apertural set within penultimate whorl.

DESCRIPTION (HOLOTYPE)

Shell of small size for the genus (height 6.8 mm, major diameter 1.9 mm), not umbilicate, dextral, slender, turrited with straight outline, rather thin, translucent, pale corneous. Whorls 10, slightly shouldered with a deep straight crenulated suture all the way to the aperture. Protoconch 2+ whorls, glossy with faint radial and spiral sculpture. Protoconch/teleoconch transition distinct because of change in macrosculpture. First whorl of teleoconch with well-defined radial ribs about same width as intercostal spaces. Surface of later teleoconch whorls with well-defined broad radial ribs much wider than intercostal spaces and with extremely faint, uneven and wavy spiral sculpture. Growth lines not visible. Aperture elongated, orthocline, with approximately 90° columellar-basal angle, cut by penultimate whorl, with faint whitish parietal callus enhanced on columellar edge. Apertural dentition of deeply sited, strong, short palatal tubercule, perpendicular short basal lamella about same distance from aperture edge as palatal one and large spirally curving downward columellar lamella. Penultimate whorl furnished with exactly the same dentition positioned half whorl from the apertural set. Peristome simple, acute, not reflected.

HABITAT. — Primary forest, under leaf litter on lateritic soil.

REMARKS

With respect to shell morphology, Ischnocion triptyx (Pilsbry,1907) (forming the monotypical genus in the Subulinidae Fischer & Crosse, 1877 ) described from Colombia,is somewhat similar.However, P.nouraguensis n. sp. is almost definitely a spiraxid and Ischnocion has a parietal lamella that has never been observed in any species of Spiraxidae .Yet,the taxonomic position of P. nouraguensis n. sp. is problematic even within the Spiraxidae . The entire family is in great need of revision since the anatomy is not known for most of the described species (see Baker 1926). What can be observed from the limited material available is that the Recent Spiraxidae are probably remnants of an ancient clade represented today by few well-defined generic level taxa,many of which are monotypic in the current classification. We hypothesise that similarity of the shape of embryonic whorls is much stronger evidence of phylogenetic relationships than the presence or the lack of apertural lamellae in this family. We also suggest that the presence of apertural lamellae in the Spiraxidae is a symplesiomorphic character that has been lost independently in many taxa. All six species of Jamaican Spiraxis Adams, 1850 (including all its subgenera), as well as Venezuelan Spiraxis (Ravenia) blandi (Crosse, 1873) have pointed protoconch and therefore we cannot describe P. nouraguensis n. sp. within this genus despite some similarities with Spiraxis (Euspiraxis) Pfeiffer, 1854 in the apertural armature. Thus, we describe P. nouraguensis n. sp. as Pseudosubulina based on the turrited shape of the shell with an obtuse apex, despite the presence of the apertural lamellae,which have never been recorded in this genus; refraining from the description of another monotypic generic level taxon, pending the revision of the family Spiraxidae . This extends the diagnosis of the genus Pseudosubulina , which now includes species with palatal teeth and columellar lamellae.

Figures

FIG. 5. — Pseudosubulina nouraguensis n. sp.: A-E, holotype MNHN 25073;B, magnified apertural dentition;C, details of protoconch sculpture; D, details of teleoconch sculpture; E, details of collumelar surface sculpture. Scale bars: A, 5 mm; B, 1 mm; C-E, 200 µm.