Wollastonia beckmanni 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 : 43

† Wollastonia beckmanni De Mattia & Groh sp. n. Figs 143-145, 146

Type material.

All from Porto Santo, SMF 348927, holotype, from loc. typ., leg. K. & C. Groh, June 6 1983; SMF 348928/5 PT, MMF 24956/1 PT, MMF 46281/1 PT, MMF 46282/1 PT, NHMW 112143/1 PT, CKG/62 PT, NMWZ 2016.013.00009/5 PT, CJG/5 PT, from loc. typ., leg. K. & C. Groh, June 6 1983; CWDM/12 PT, E of Vila Baleira, S slope of the hill above Vale do Touro, 50 m W of the oil tanks, excavated Quaternary mixed gravel, 33°03'47"N / 16°19'26"W, 24 m, leg. W. De Mattia & J. Macor, May 24 2015; CFW 12176/5 PT, E of Vila Baleira, S slope of the hill above Vale do Touro, W of the oil tanks, [(sub-)fossil slope-deposits of] red gravel, 33°37'52"N / 16°19'26"W, 25 m, leg. F. Walther, Apr. 5 2017; ANSP H 11843/2 PT [sub H. leacockiana ], Vale do Touro, 33°03'46"N / 16°19'29"W, 15 m a, leg. J. Gerber, K. Groh & J. Hemmen, Aug. 16 1985.

Locus typicus.

Porto Santo, south coast, ditch near the harbour built in 1985 at Vila Baleira, lens of quaternary calcareous aeolinite within a marine sandy beach terrace (nowadays beyond the quay of the harbour), 33°03'50"N / 16°18'56"W, 0-1.5 m.

Diagnosis.

Small Wollastonia species with a very depressed body whorl that is finely granulated; umbilicus very wide in relation to maximum diameter, rather eccentric.

Description of the shell of the holotype.

Shell small for the genus, with 5.15 rapidly increasing whorls, the protoconch measures 1.5 whorls. The form of the shell is flat conical, the convex teleoconch whorls show a strongly keeled periphery. The last whorl measures 65%, the penultimate whorl 14% of the total shell height. The lower half of the body whorl is slightly concave beneath the keel in frontal view near the periphery and otherwise regularly convex. The suture between the whorls is simple and slightly impressed. The aperture, which is inclined to the vertical axis of the shell in an angle of 58° and descending in the last 5% of the last whorl in an angle of 43° to the horizontal axis, has an elongate-ovate form, its width measures 42% of the total shell width, its height 27% of the total shell height. It has a distinctly reflected lip, which is completely detached from the body whorl. The very eccentric umbilicus, which measures 17% of the total shell width, is in the upper whorls narrowly perspective. The protoconch is smooth, the teleoconch shows a low number of oblique radial ribs, nine in the penultimate quadrant of the body whorl and is additionally covered by many fine tubercles. The number of tubercles in the standard quadrate of the base is 102; the tubercles become coarser towards the centre of the base and finer towards the periphery. There are no traces of colouration (see Fig. 143).

Variation in paratypes.

The size varies slightly, and the density of the tubercles in the standard quadrate of the base may vary by ± 10%. Exceptionally, the umbilicus may be narrower and the angles of the aperture to the vertical axis and the descending of the last part of the body whorl to the vertical axis also slightly vary (see Measurements section below). Nevertheless, the overall shape and sculpture of all paratypes is very close to that of the holotype. In a few shells traces of a brownish colouration are perceptible, however there are no traces of a banding pattern (see Figs 144-145).

Measurements.

D 5.3 ± 0.2 mm (range 5.0-5.6 mm); H 3.3 ± 0.2 mm (range 3.2-3.5 mm); FW 2.2 ± 0.1 mm (range 2.1-2.3 mm); PA 72.0 ± 3.0° (range 66.0-76.0°); DU 0.4 ± 0.05 mm (range 0.3-0.4 mm); NW 6.2 ± 0.2 (range 6.0-6.4) (n = 20). Ratio D/H 1.6; ratio FW/H 0.7.

Distribution.

Wollastonia beckmanni sp. n. is known only from the southeastern coast of Porto Santo, from the hill immediately east of Vila Baleira (mud deposits at Vale do Touro) to the aeolinite deposits behind the new harbour. See map in Fig. 146.

Etymology.

Named after the late German entrepreneur and self-taught malacologist Dr. Karl-Heinz Beckmann (1948-2007) to honour his valuable contributions to the malacofauna of different islands and archipelagos in the Mediterranean and the Atlantic.

Comparison and comments.

Because of its small size the new species can only be confused with small H. aucta Wollaston, 1878, which have, however, a higher and more distinctly stepped spire, have two well-developed keels and much coarser and more sparsely set tubercles on the shell surface. Hystricella microcarinata sp. n. has a much higher, rounded conical form, two keels on the body whorl, coarser and less densely set tubercles, a much narrower umbilicus, and a different shape and differently positioned angles of the aperture.

Taxonomic remarks.

As with other subfossil Wollastonia species, W. beckmanni sp. n. is included in this genus because it considerably differs from Hystricella and is similar to W. oxytropis in surface sculpture and overall shell shape.

Status and conservation.

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