Hystricella echinoderma (Wollaston, 1878)

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 : 22-23

† Hystricella echinoderma (Wollaston, 1878) Figs 95, 96

List of synonyms.

1878 Helix (Hystricella) echinoderma Wollaston: 159-160.

1894 Geomitra echinoderma - Pilsbry in Pilsbry 1893-1895: 242.

1931 Geomitra (Actinella) echinoderma - Nobre: 88.

1950 Discula (Hystricella) echinoderma - Mandahl-Barth 1950: 31, 55.

1983 Discula (Hystricella) echinoderma - Waldén: 267.

2002 Geomitra echinoderma - Bank et al.: 124.

2008 Hystricella echinoderma - Seddon: 80.

Type material.

NHM 1875.02.02-52, lectotype (herewith designated) from loc. typ.; NHM 1875.02.02-53 to -54, 2 paralectotypes, from loc. typ.

Locus typicus.

Portum Sanctum, semifossilis; recens haud observata.

Original description.

From Wollaston 1878: T. trochiformis, subtus subplanulata perforata, undiquegranulis magnis obtusis sat dense obsita; spira elevata; anfractibus convexis, subgibbosis, ultimo subtectiformi acute carinato (carina simplici, solum antice gradatim obsolete subduplici); umbilico punctiformi, aperto; apertura subovali-rotundata, labris continuis conjunctis, peristomate simplici, expanso, subrecurvo, tenui, relevato. - Long. axis 2 ½ lin.; diam. 3 ½.

Description of the lectotype.

Shell large for the genus, with 6¾ regularly increasing whorls, the protoconch with 1.9 whorls. The form of the shell is high conical, the convex to quadrangular teleoconch whorls showing two more and more expressed angulations which form in the last whorl two rounded keels, the upper less developed than the lower one. The last whorl measures 59%, the penultimate whorl 14% of the total shell height. The lower 70% of the body whorl are situated below the peripheral keel which is slightly constricted by a concavity below the periphery in frontal view. The base is convex, slightly straightening towards the umbilicus. The two keels of the body whorl are located in the upper ⅛ and ⅓ of the total height of the body whorl. The suture between the whorls is simple but deeply sunken. The aperture, which is inclined to the vertical axis of the shell in an angle of 48° and descending in the last 5% of the last whorl in an angle of 38° to the horizontal axis, has an oblique-ovate form, its width amounts to 43% of the total shell width, its height to 34% of the total shell height. It has a slightly reflected lip, which is completely detached from the body whorl. The centered umbilicus, which measures 10% of the shell’s total width, is in the last whorls circular, but completely closed deeper inside. The protoconch is smooth, the teleoconch shows a number of oblique radial ribs, 15 in the penultimate quadrant of the body whorl, and is additionally covered by numerous irregularly arranged, elongate, rough tubercles. The number of tubercles in the standard-quadrate of the base is 81. There are no traces of colouration. See Fig. 95.

Measurements.

D 7.0 mm; H 5.9 mm; FW 3.5 mm; PA 42.2°; DU 0.5 mm; NT ≈ 35; NW 6.6 (n = 1). Ratio D/H 1.2; ratio FW/H 0.5.

Distribution.

Hystricella echinoderma is only known from Fonte da Areia in the northern part of Porto Santo (Fig. 96).

Comparison and comments.

Hystricella echinoderma can be confused on first glance with comparatively large-sized species of the genus Wollastonia like W. vermetiformis , W. ripkeni sp. n., and W. falknerorum sp. n.; from these it is distinguishable by the lack of one or two sharply pointed keels, respectively, a much rougher sculpture, a non-eccentric umbilicus, and the stepped, high conical form. From the similarly sized W. subcarinulata and W. inexpectata sp. n. it is separated by a wider or non-eccentric umbilicus, a relatively higher shell, the quadrangular instead of convex rounded whorls, a coarser granulation and the oblique-ovate instead of straight horizontally elliptical aperture. From the similar shaped H. echinulata and H. microcarinata sp. n. it is easily distinguishable by the much larger size.

Taxonomic remarks.

Wollaston (1878) compares H. echinoderma with the rather similar H. echinulata and calls it a monstrous sister species of that species, citing as examples of pairs of nominal species with a distinct size difference Helix vermetiformis and H. bicarinata , H. Lowei and H. portosanctana as well as H. bowdichiana and H. punctulata .

Status and conservation.

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