Wollastonia inexpectata De Mattia & Groh

Mattia, Willy De, Neiber, Marco T. & Groh, Klaus, 2018, Revision of the genus-group Hystricella R. T. Lowe, 1855 from Porto Santo (Madeira Archipelago), with descriptions of new recent and fossil taxa (Gastropoda, Helicoidea, Geomitridae), ZooKeys 732, pp. 1-125 : 61-62

† Wollastonia inexpectata De Mattia & Groh sp. n. Figs 200-202, 203

Type material.

SMF 348930, holotype, from loc. typ., leg. W. De Mattia, May 23 2015 (see Fig. 200); NMWC 80.202 Acc. 55 158/1 PT as " Geomitra oxytropis Lowe var. subcarinulata Woll. Porto Santo" (Figs 201-202).

Locus typicus.

N of airport, end of the runway towards Fonte de Areia, Quaternary calcareous sand deposit, 33°05'25"N / 17°20'58"W, 99 m.

Etymology.

Wollastonia inexpectata sp. n. was unexpectedly found during intensive field researches at Fonte da Areia when looking for H. echinoderma .

Diagnosis.

Shell large for the genus, solid and conical. Whorls rounded, with deep sutures. The shell’s surface covered with small and densely set tubercles. Body whorl with a peripheral, rounded keel. Other teleoconch whorls without visible keel. Umbilicus narrow but open. Last whorl descending toward the aperture. Aperture oval with continuous peristome.

Description of the shell.

The shell is large for the genus and rather conical, with 6.3 regularly increasing whorls. The protoconch has 1.7 smooth whorls. The teleoconch whorls are distinctly convex and separated by a slightly impressed but simple suture. The body whorl measures 64% and the penultimate whorl 14% of total shell height and is descending towards the aperture in its last 5% in an angle of 36°. It has a rounded angulation in its upper third (in relation to total shell height) that is emphasised by a narrow, only slightly concave impression below the periphery. The lower part of the body whorl (beneath the periphery in frontal view) is otherwise rather convex. The aperture is regular elliptical, measuring 49% of the total shell width and 29% of the total shell height. It is inclined to the vertical axis of the shell in an angle of 57°. The peristome is completely detached from the body whorl, expanded and distinctly reflected, especially in its basal and columellar part. The umbilicus is eccentric, closed in the early whorls, but pinhole-like in the body whorl, measuring 5% of the maximum shell diameter. The sculpture of the teleoconch consists of oblique radial ribs (10 in the penultimate quadrant of the body whorl) and numerous, small roundish tubercles (132 in the standard square basal surface of the shell). The colour is only preserved as a yellowish hue on the teleoconch, a slightly darker yellowish, narrow spiral band in the middle of the base and a lighter marked keel. See Figs 200-202.

Measurements.

D 8.6 mm; H 6.7 mm; FW 4.6 mm; PA 41.2°; DU 0.6 mm; NT 132; NW 6.6 (n = 1). Ratio D/H 1.3; ratio FW/H 0.7.

Distribution.

The species is only known from the type locality. A second specimen is known from another unidentified locality in Porto Santo and housed at the NMW. The distribution is shown in Fig. 203.

Comparison and comments.

Wollastonia inexpectata sp. n. is superficially similar to H. echinoderma , or W. vermetiformis and W. falknerorum sp. n. but is readily distinguishable from these species by the lack of a second keel, its much finer sculpture, narrower umbilicus and regular conical form. From H. echinoderma it can also be distinguished by its regular convex and not stepped whorls and the regular elliptical rather than oblique ovate aperture. From the similarly sized W. subcarinulata it differs in the narrower umbilicus, the presence of a rounded keel, the finer granulation and the higher shell in relation to its width.

Taxonomic remarks.

Wollastonia inexpectata sp. n. is included in the genus Wollastonia because it is similar to W. oxytropis in size and surface sculpture. It is noteworthy that the similarly large-sized Hystricella echinoderma most probably also originates from the Quaternary deposits in the north of the island, and likewise is extremely rare there.

Status and conservation.

Extinct before the islands’ scientific exploration in the 19th century, possibly already before human settlement.