Hystricella bicarinata (G. B. Sowerby I, 1824)

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 : 9-14

Hystricella bicarinata (G. B. Sowerby I, 1824) Figs 31-32, 33-37, 38-45, 46-53, 54

List of synonyms.

1824 Helix bicarinata G. B. Sowerby I: 58, pl. 3 fig. 7.

1828 Helix bicarinata - Wood: pl. 8 fig. 85.

1831 Helix duplicata R. T. Lowe: 58, pl. 6 fig. 30 [unjustified replacement name for Helix bicarinata Sowerby I, 1824 [non Helix C.[ochlitoma] bicarinata J. Férussac, 1821, a secondary homonym of Bulimus bicarinatus Bruguière, 1792 = Archachatina bicarinata ( Bruguière, 1792). See Taxonomic Remarks below].

1846 Helix bicarinata - L. Pfeiffer: 141, pl. 91 figs 8-11.

1847 Helix bicarinata - L. Pfeiffer in L. Pfeiffer 1847-1848: 190.

1854 Helix bicarinata - Reeve in Reeve 1851-1854: pl. 142 figs 908-909.

1854 Helix (Ochthephila) bicarinata - Albers: pl. 9 figs 1-4.

1855 Helix (Hystricella) bicarinata - R. T. Lowe: 186.

1867 Helix (Octephila) bicarinata - Paiva: 45.

1878 Helix (Hystricella) bicarinata - Wollaston: 161-163.

1888 Helix bicarinata - Tryon in Tryon and [Pilsbry] 1888: 33, pl. 7 fig. 90.

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

1931 Geomitra (Actinella) bicarnata - Nobre: fig. 37.

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

1966 Discula (Hystricella) bicarinata - S. G. A. Jaeckel: 53.

1983 Discula (Hystricella) bicarinata bicarinata - Waldén: 267.

2002 Geomitra bicarinata bicarinata - Bank et al.: 124.

2008 Hystricella bicarinata - Seddon: 79, pl. 29 fig. E, map 178.

2011 Hystricella bicarinata - Seddon: e.T6724A12800659.

Type material.

Despite intensive research in multiple museum collections (NHM, NMW, MMUE, ANSP, NHC, NMS, OUMNH, RAM, SMF) that could have held the type material of the taxon, no such material could be traced and therefore we deem it reasonable to assume that the type material is lost. To stabilise the present interpretation of Helix bicarinata G. B. Sowerby I, 1824 and to clarify its taxonomic status we designate a neotype here, which is deposited in the collection of the SMF under the No. SMF 348936 (see Fig. 33). The original figures of Helix bicarinata G. B. Sowerby I, 1824 from Sowerby (1824: pl. 3 fig. 7) 32 and Helix duplicata R. T. Lowe, 1831 from R. T. Lowe (1831: pl. 6 fig. 20) are depicted in Figs 31-32. The neotype (Fig. 33) is consistent with the figure in Sowerby (1824: pl. 3 fig. 7) and the original description (see below), especially with regard to size, shape and the presence of two keels on the body whorl. The taxon was originally described from Porto Santo without more detailed locality data, which is consistent with origin of the specimen selected as neotype.

Locus typicus.

Pico do Castelo, S slope around the Miradouro, under stones in pine wood, 33°04'42"N / 16°20'00"W, 270 m (through the designation of the neotype).

Further material examined.

All from Porto Santo, ANSP H 20185/13, NW slope of Pico Branco, 33°05'50"N / 16°18'57"W to 33°05'52"N / 16°18'49"W, 150-200 m, leg. J. & C. Hemmen, Jan. 8 1981; ANSP H 11776/2, NW slope of Pico de Juliana, 33°05'34"N / 16°19'25"W, up to 450 m, leg. J. & C. Hemmen, Jan. 6 1981; CKG/12, Pico de Juliana, under stones, 33°05'31"N / 16°19'20"W, 365 m, leg. K. Groh, Jun. 23 1983; ANSP H 11788/11, CMN/3, SW slope of Pico do Juliana, 33°05'30"N / 16°19'23"W, 360 m, leg. J. Gerber, K. Groh & J. Hemmen, Aug. 13 1985; CFW 11149/1, Pico Juliana, old quarry on the southern slope, 33°05'28"N / 16°19'17"W, 330 m, leg. F. Walther & E. M. Gryl, Apr. 3 2017; ANSP H 11769/3, Ribeiro das Esmoitadas (E Camacha), 33°05'27"N / 16°20'17"W, 130 m, leg. J. Gerber, K. Groh & J. Hemmen, Aug. 13 1985; CKG/2, SW of Pico de Juliana, 33°05'14"N / 16°19'32"W, 360 m, leg. K. & C. Groh, Oct. 27 1980; CFW 11158/10, Pico do Facho, NW slope, 33°05'12"N, 16°19'38"W, 370 m, leg. F. Walther, Apr. 3 2017; ANSP H 20186/1, NE slope of Pico do Facho, 33°05'07"N / 16°19'23"W, 430-450 m, leg. K. Groh & J. Hemmen, Jun. 28 1983; CWDM/6, CMN/ 3, ridge between Pico do Facho and Pico da Gandaia, stone walls, 33°05'04"N / 16°19'21"W, 460 m, leg. W. De Mattia & J. Macor, May 25 2015; CWDM/15, N slope of Pico do Facho in Tamarix wood, under stones, 33°05'04"N / 16°19'25"W, 475 m, leg. W. De Mattia & J. Macor, May 25 2015; CKG/44, CMN/6, W of Pico do Facho, under stones, 33°05'04"N / 16°19'33"W, 450 m, leg. K. Groh, Jun. 29 1983; ANSP H 11778/c. 40, SW slope of Pico do Facho, 33°05'03"N / 16°19'31"W, 460-480 m, leg. K. Groh & J. Hemmen, Jun. 28 1983; CKG/24, CMN/44, upper Ribeira Formosa between Covau and Serra de Fora, under stones, 33°05'02"N / 16°19'14"W, 140 m, leg. K. Groh, Jun. 19 1983; ANSP H 11775/13, W slope of Pico do Facho, 33°05'02"N / 16°19'38"W, leg. J. & C. Hemmen, Jan. 6 1981; ANSP H 11834/19 [sub H. echinulata ], summit of Pico da Gandaia, 33°05'01"N / 16°19'14"W, 440 m, leg. J. & C. Hemmen, Jan. 6 1981; CWDM/11, CMN/7, Pico da Gandaia, southern rocky cliffs close to the top, under stones, 33°05'01"N / 16°19'14"W, 440 m, leg. W. De Mattia & J. Macor, May 25 2015; ANSP H 11779/24, SW slope of Pico do Facho, 33°04'56"N / 16°19'39"W to 33°05'02"N / 16°19'30"W, 300-450 m, leg. K. Groh & J. Hemmen, Jul. 1 1983; CWDM/15, CMN/3, N and E slopes and summit of Pico do Castelo, under stones in pine wood, 33°04'55"N / 16°20'07"W, 350 m, leg. W. De Mattia & J. Macor, May 22 2015; CWDM/25, CMN/5, S slope of Pico do Facho, along path at the S border of the pine wood, under stones, 33°04'52"N / 16°19'26"W, 355 m, leg. W. De Mattia & J. Macor, May 17 2015; CKG/8, Pico do Castelo, S slope around the Miradouro, under stones in pine wood, 33°04'51"N / 16°20'03"W, 420 m, leg. K. & C. Groh, Oct. 27 1980; CWDM/22, CMN/4, Ribeira da Areia, serpentine 240 m NNW the quarry, under stones, 33°04'51"N / 16°18'41"W, 140 m, leg. W. De Mattia & J. Macor, May 21 2014; ANSP H 11787/c. 30, approx. 1 km NE Capela da Graça, 33°04'49"N / 16°19'04"W, 250 m, leg. J. & C. Hemmen, Jan. 4 1981; CWDM/12, CMN/4, lake shore S of Ribeira da Serra de Dentro, under stones and in stone walls, 33°04'48"N / 16°18'31"W, 70 m, leg. W. De Mattia & J. Macor, May 22 2015; ANSP H 20187/1, NW slope of Pico do Concelho, 33°04'44"N / 16°18'04"W to 33°04'43"N / 16°18'01"W, 250-300 m, leg. K. Groh & J. Hemmen, Jul. 29 1983; CKG/8, CMN/8, Pico do Concelho, NW of the top, under stones, 33°04'43"N / 16°17'59"W, 260 m, leg. K. Groh, Jun. 29 1983; ANSP H 11835/12 [sub H. echinulata ], NW slope of Pico do Concelho, 33°04'43"N / 16°18'01"W, approx. 280 m, leg. J. & C. Hemmen, Jan. 6 1981; ANSP H 12780/32, NW slope of Pico do Concelho, 33°04'43"N / 16°18'01"W, 250-300 m, leg. K. Groh & J. Hemmen, Jun. 6 1983; CWDM/15, CMN/2, summit of Pico do Concelho, under stones, 33°04'42"N / 16°18'01"W, 280 m, leg. W. De Mattia & J. Macor, May 18 2015; CWDM/18,CMN/4, Pico do Castelo, S slope around the Miradouro, under stones in pine wood, 33°04'42"N / 16°20'00"W, 270 m, leg. W. De Mattia & J. Macor, Feb. 12 2012; CMN/1, Pico do Castelo, S slope around the Miradouro, under stones in pine wood, N slope, 33°04'42"N / 16°20'01"W to 33°04'51"N / 16°20'03"W, 300-430 m, leg. K. Groh Jul. 1 1983; ANSP H 11783/24, Pico do Castelo, 33°04'42"N / 16°20'01"W to 33°04'51"N / 16°20'03"W, 350-430 m, leg. K. Groh & J. Hemmen, Jul. 1 1983; CWDM/8, CMN/4, path from Capela da Graça to Pico do Castelo along the Levada, under stones, 33°04'38"N / 16°19'48"W, 165 m, leg. W. De Mattia & J. Macor, May 17 2015; CKG/3, CMN/68, Capela da Graça up to Pico de Facho-Motos de Fora, under stones, 33°04'38"N / 16°19'33"W, 200 m, leg. K. Groh, Jun. 23 1983; ANSP H 11785/9 spms, Ribeiro do Formoso, 33°04'36"N / 16°19'04"W, 130 m, leg. J. Gerber, K. Groh & J. Hemmen, Aug. 13 1985; ANSP H 11777/12, approx. 1 km S Serra de Dentro, 33°04'33"N / 16°18'25"W, 160 m, leg. J. & C. Hemmen, Jan. 8 1981; ANSP H 11782/c. 30, slope between the SE slope of Pico do Castelo and Capela da Graça, 33°04'32"N / 16°19'38"W, 160 m, leg. J. & C. Hemmen, Jan. 4 1981; CFW 11161/7, Casinhas, N of Capela da Graça, 33°04'27"N / 16°19'27"W, 150 m, leg. F. Walther, Apr. 4 2017; CKG/11, CMN/1, Pico do Baixo, 33°04'26"N / 16°19'44"W to 33°04'46"N / 16°19'44"W, 100-250 m, leg. K. Groh, Jul. 11, 1983; CWDM/23, Engula, under stones, 33°04'19"N / 16°19'01"W, 150 m, leg. W. De Mattia & J. Macor, May 18 2015; CFW 11159/>10, E slope of Rocha de Nossa Senhora, 33°04'19"N / 16°19'01"W, 150 m, leg. F. Walther, Apr. 3 2017 ANSP H 11771/18, N of Portela (E of Vila Baleira), 33°04'07"N / 16°19'17"W, 120 m, leg. J. & C. Hemmen, Jan. 4 1981; CKG/2, CMN/1, Capela da Graça up to Pico do Facho-Motos de Fora, N slope, 33°04'38"N / 16°19'33"W to 33°05'04"N / 16°19'33"W, approx. 200-450 m, leg. J. Gerber, K. Groh & J. Hemmen, Jun. 28 1985; ZMH 120610/2, foot of Pico do Castelo, c. 33°04'37"N / 16°19'49"W, 170 m, ex coll. W. Fauer, leg. J. & C. Hemmen, Jul. 11 1983; ZMH 110165/68, slopes of Pico do Facho, under stones; c. 33°04'59"N / 16°19'25"W, 430 m a.s.l., leg. E. Clauss, Sep. 22 1992; ZMH 24288/2, Madeira Archipelago, without exact locality data, ex coll. Altonaer Museum; ZMH, 24289/1, Porto Santo, without exact locality data, ex coll. Museum Klagenfurt; ZMH 24290/3, Porto Santo, without exact locality data, ex coll. Altonaer Museum, ex coll. O. Semper, ex coll. Dohrn.

Original description.

From Sowerby (1824): testa subglobosa, spira breviuscula, subconica; anfractibus quinque quadratis, mediane carinis duabus, superiore obtusiuscula: apertura integra, rotunda, peristomate distincto: umbilico parvo. Axis 3∕16, diam. ¼ unc.

Diagnostic features of the shell.

Shell as in the genus description. The main diagnostic feature is the presence of two well-developed keels along the penultimate and body whorl. The lower keel is usually slightly stronger and more evident than the upper one along both whorls. The overall shape of the shell of Hystricella bicarinata is always conical and scalariform by virtue of a “shoulder” that lets the contour of the whorls appear markedly angular. The sutures are deep and well-marked (see Figs 33-37).

Measurements.

D 4.9 ± 0.2 mm (range 4.4-5.3 mm); H 3.8 ± 0.2 mm (range 3.4-4.2 mm); FW 2.4 ± 0.2 mm; PA 53.5 ± 2.4°; DU 0.4 ± 0.09 mm; NT 21 ± 6; NW 5.6 ± 0.1 (range 5.1-5.75) (n = 40). Ratio D/H 1.3; ratio FW/H 0.6.

Body.

Body as in the genus description.

Genital anatomy.

As in the genus description. The albumen gland is long and connected to an equally long sperm-oviduct. The prostatic part extends into a thin vas deferens that is twice as long as the sperm-oviduct. The free oviduct is somewhat variable in length, but is usually three to four times shorter than the vagina. The duct of the bursa copulatrix is usually wide, slightly shorter than the penis, opening out into a roundish, small bursa copulatrix. One tuft of digitiform glands consisting of two, more rarely three never branching glands. The inner ornamentation of the vagina consists of very wide, low, and smooth pleats running longitudinally as far as the genital atrium. The penial flagellum is short, remarkably cylindrical and with a blunt apex. It is usually as long as the epiphallus. Its internal walls are completely smooth. The epiphallus is short and its internal walls are smooth. The penis lacks any muscular or glandular sheath. It is thick-walled and approximately four times longer than the flagellum. It is cylindrical and sometimes slightly swollen in its distal part. The inner walls of the penis are usually smooth or with very smooth, little elevated and spaced pleats which run longitudinally and reach the genital atrium (see Figs 38-53).

Distribution.

Hystricella bicarinata is endemic to the island of Porto Santo (Madeiran Archipelago, Portugal) (Fig. 54). The species is restricted to the eastern, mountainous part of the island and is present only in the central section of this area. It is commonly found on the slopes of Pico do Castelo, Pico do Facho, Pico de Juliana, Pico da Gandaia, Rocha de Nossa Senhora, and the western slopes of Pico do Concelho. It is also commonly found at lower elevations of the Serra de Dentro, Barranco Branco, and Lombo de Paredes. It is not present on the small islets surrounding the main island, namely Ilhéu de Cima, Ilhéu de Baixo, and Ilhéu de Ferro. Subfossil representatives of Hystricella bicarinata are not known. Seddon (2008: 181) depicts the distribution of H. bicarinata . The four southernmost points indicate the presence of the species also for the southern ridge of eastern Porto Santo. We here infer that these localities are based upon misidentifications with other species, probably some representatives of Wollastonia , i.e., W. jessicae sp. n. or W. klausgrohi sp. n.

Ecology.

Hystricella bicarinata is commonly found under volcanic rocks scattered on grassland in open fields that are more or less sloping. It has also been found under stones in pine woods (Pico do Castelo) or in cracks and crevices on rocky walls (Pico da Gandaia) or terraced areas (southern slopes of Pico do Castelo). The specimens aestivate on the lower surfaces of stones or rocks, frequently forming large clusters of 40 to 50 individuals attached one to another. Under a single stone of roughly 60 × 40 cm approximately 200 individuals were observed (southern slopes of Pico do Facho).

Comparison and comments.

The presence of two keels along the body whorl easily distinguishes H. bicarinata from H. echinulata . Where both taxa come into contact in the northern to northeastern part of Porto Santo (Fig. 4) intermediate populations exist however, suggesting a possible hybrid zone (see below).

At first glance, and due to the small dimensions, H. bicarinata can be confused with the fossil species H. aucta and H. microcarinata sp. n. (see Fig. 74). However, a closer analysis reveals major differences in many features of the shell. Hystricella aucta has a more solid shell with two, almost equally developed keels along the body whorl. The penultimate and the third whorl have a single strong upper keel only. The tubercles in H. aucta are much smaller and finer than in H. bicarinata (see Figs 71-73).

Hystricella microcarinata sp. n. resembles H. bicarinata with regard to dimensions and overall shape; however, the weak keels along the penultimate and body whorl and the well-developed and rather elevated growth lines allow the separation of the two species. Moreover, the tubercles in H. microcarinata sp. n. are somewhat smaller and more scattered.

Hystricella bicarinata can also resemble some of the species included in the newly described genus Wollastonia gen. n. Species such as W. turricula , W. leackociana and W. oxytropis differ in the very fine granulation present on the shell’s surface. These species do not possess evident tubercles but only small granules that are remarkably smaller in dimension than the tubercles of H. bicarinata . Moreover, the overall shape of all three above-mentioned species is different from that of H. bicarinata (see e.g. Figs 100, 119, 130). Other (sub-) species assigned to Wollastonia gen. n. such as W. vermetiformis , W. jessicae jessicae sp. n., W. jessicae monticola ssp. n., and W. klausgrohi sp. n. (see Figs 118-120, 147-149, 159-161, 168-170) are somewhat similar to and could be confused with H. bicarinata . These taxa can be readily distinguished, however, by their more scalariform shape, somewhat stronger keels, and the sparser arrangement of the tubercles. Moreover, the distributional ranges of Hystricella and Wollastonia gen. n. do not significantly overlap and molecular data strongly supports differentiation at the genus-level (thus also at species level).

Nomenclatural and taxonomic remarks.

We report below a statement sent to us by Ruud Bank referring to the erroneously introduced name Helix duplicata R. T. Lowe, 1831. "The name Helix [ Cochlitoma ] bicarinata A. Férussac, 1821 does not exist! Férussac simply reclassified Bulimus bicarinatus Bruguière, 1792 under Helix (Cochlitoma) . Thus, Helix bicarinata G. B. Sowerby I, 1824 was at that time (and only for a very short period of time) a secondary homonym of Helix bicarinata ( Bruguière, 1792). Helix duplicata R. T. Lowe, 1831 was introduced to replace the name of Sowerby due to homonymy with the Férussac name, but as stated above, Férussac did not introduce such a name, it was simply a generic change for Bulimus bicarinatus Bruguière. In my opinion, the name duplicata cannot be considered a nomen novum. It would have been only a nomen novum when R. T. Lowe mentioned Bruguière as the author of the senior taxon - what he didn’t.

Mandahl-Barth (1950), Jaeckel (1966) and Waldén (1983) placed this taxon in Discula and considered Hystricella as a subgenus. Bank et al. (2002) considered the species to belong to a distinct genus (under the name Geomitra ). Only recently Seddon (2008) appointed this species to the genus Hystricella and emphasised anatomical differences with the genus Discula .

Status and conservation.

The opinion of Seddon (2011a) "[Hystricella bicarinata] has a total extent of occurrence of 10 km2 but is present over the eastern part of the island and in these sites it is abundant" has been confirmed by our field researches. For this reason, we think that the assessment as Near Threatened (NT) is appropriate at present.