Wollastonia turricula (R. T. Lowe, 1831) R. T. Lowe, 1831

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 : 27-31

Wollastonia turricula (R. T. Lowe, 1831) comb. n. Figs 99-102, 103-111, 112

List of synonyms.

1831 Helix turricula R. T. Lowe: 58, pl. 6 fig. 21.

1846 Helix turricula - L. Pfeiffer: 141, pl. 91 figs 5-7.

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

1854 Helix turricula - Reeve in Reeve 1851-1854: pl. 138 fig. 867.

1854 Helix (Ochthephila) turricula - Albers: 37, pl. 9 figs 11-13.

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

1867 Helix (Octephila) turricula - Paiva: 47.

1878 Helix (Hystricella) turricula - Wollaston: 163-165.

1878 Helix (Hystricella) turricula var. ss pererosa Wollaston: 165.

1888 Helix turricula - Tryon in Tryon and [Pilsbry] 1888: 33, pl. 7 fig. 91.

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

1923 Ochthephila turricula - Watson: 283-293, pl. 6 figs 1-10.

1931 Geomitra (Actinella) bicarnata - Nobre: 88, fig. 38.

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

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

1977 Discula (Hystricella) turricula - Pettitt: 147-150.

1983 Discula (Hystricella) turricula - Waldén: 267.

2002 Geomitra turricula - Bank et al.: 124.

2008 Hystricella turricula - Seddon: 79, pl. 29 fig. b, map 181.

2009 Hystricella turricula f. pererosa - Groh et al.: 21 fig. 28.

2011 Hystricella turricula - Seddon: e.T6723A12800477.

Type material.

[turricula], NMH 1968.578, lectotype (herewith designated), from loc. typ., ex coll. R. T. Lowe; NMH 1948.7.8.35, 1 paralectotype, from loc. typ., ex coll. R. T. Lowe. The original figure of Helix turricula R. T. Lowe, 1831 (from Lowe 1831: pl. 6 fig. 21) is depicted in Fig. 99, the lectotype (Phot. P. Crabb, NHM) in Fig. 100; [pererosa], RAM EXEMS-1720-1909-d39-74a, lectotype (herewith designated), from loc. typ., ex coll. Linter, ex coll. T. V. Wollaston; RAM EXEMS-1720-1909-d39-74b, 1 paralectotype, from loc. typ., ex coll. Linter, ex coll. T. V. Wollaston (see Figs 113-115).

Loci typici.

[turricula], Hab. in Insula quadam "Ilheo de Cima" dicta, juxta Insulam Portum Stum; [pererosa], 'Ilheo de Cima’.

Further material examined.

All from Porto Santo. Fossil: CKG/10, CWDM/2, ZMH 116090/1 fragm [ex coll. E. Clauss], Quaternary slope deposits at the SW coast of the Ilhéu de Cima, 33°03'15"N / 16°17'02"W, 40 m, leg. K. & C. Groh & J. & C. Hemmen, Jun. 26 1983 and leg. J. Gerber, K. Groh & J. Hemmen, Aug. 17 1985. Recent: CKG/9, Ilhéu de Cima, top, under stones, 33°03'13"N / 16°16'48"W, approx. 100 m, leg. K. & C. Groh, Oct. 25 1980; CKG/7, CMN/29, ANSP H 11918/42, ZMH 120611/1 [ex coll. W Fauer], Ilhéu de Cima, top, under stones, 33°3'13"N / 16°16'48"W, approx. 100 m, leg. K. & C. Groh & J. & C. Hemmen, Jun. 26 1983; ANSP H 11918/17, Ilhéu de Cima, top, under stones, 33°3'13"N / 16°16'48"W, approx. 100 m, leg. J. Gerber, K. Groh & J. Hemmen, Aug. 17 1985; ZMH 24296/1, Porto Santo, without exact locality data, ex coll. Altonaer Museum, ex coll. O. Semper, ex coll. Dohrn; ZMH 24297/1, Porto Santo, without exact locality data, ex coll. Museum Klagenfurt; ZMH 24298/1, Porto Santo, without exact locality data, ex coll. Altonaer Museum.

Original descriptions.

[turricula]: From Lowe 1831: H. testa turrita, pyramidata, sub-cylindrica, bicarinata, perforata, tota minute et confertissime granulata, fusca, fere unicolore, vel supra obsolete fasciata: spira valde elevata, obtusissima; sutura distincta; anfractibus bicarinatis, carinis æqualibus, prominentibus, distinctis, sulco divisis: apertura rotunda; peristomate continuo, circinato, disjuncto, tenui, reflexo. Axis 4 lin. Diam. 3. Anfr. 8 –8½; [pererosa]: From Wollaston 1878: ... a keel, very largely developed in the 'α. pererosa,' in the centre of each, causing the basal volution to be strongly bicarinated ….. var. ß. pererosa. - Plerumque obscurior, spira breviore, anfractibus in medio multo grossius carinatis (carina altissima), ultimo sensim latiore necnon antice obsolete subtortuoso, fere quasi superimposito, apertura submajore.

Redescription of the shell.

The shell is dextral and hairless. It is remarkably elongated and scalariform with deep sutures. The protoconch is from whitish to completely dark brown with 1.5 to 2 whorls. It is finely granulated along the first whorl and shows also fine radial striae and extremely small, scattered tubercles along its remaining portion. The teleoconch has from 6.9 to 7.2 rapidly increasing whorls. It is usually reddish brown, with brick red and/or dark violet shades in colour. The dark areas of the shell are mottled with more or less light brown to whitish areas, usually placed longitudinally and slightly slanting. In some specimens, the lighter areas tend to be more evident along the keels. No band pattern is visible along the upper whorls. On the lower part of the last whorl there is sometimes one dark, indistinct band that is usually very narrow. The area around the umbilicus is usually the lightest in colour. The shell is usually covered by fine debris serving as a camouflage.

The spire is very high and remarkably conical in shape. Two evident keels start already from the second whorl of the teleoconch. The keels gradually strengthen, reaching their maximum extent along the body whorl. The lower and the upper keel are more or less equally developed, the lower only sometimes slightly more pronounced. The lower whorls (especially the fourth and fifth) form a “shoulder” giving the whorls an angular contour. The sutures are deep and well marked.

The external surface does usually not show fine growth lines, except for some strong, more or less regularly spaced ribs along the top and bottom of the body whorl. Irregularly arranged, fine tubercles are present all over the teleoconch, also along the edges of the keels the tubercles remain well-separated not forming a peripheral chord.

The last whorl is not distinctly wider than the penultimate whorl, nevertheless abruptly descending near the aperture. The umbilicus is very narrow, almost closed, and somewhat eccentric. The aperture is elliptical with a faint thickening along the columellar portion of the stoma. Sometimes this thickening can also extend as far as the parietal side of the aperture. The peristome is continuous and detached from the body whorl, reflected, with the columellar margin somewhat thicker and more distinctly reflected (Figs 101-102).

Measurements.

D 6.6 ± 0.4 mm (range 6.1-7.0 mm); H 8.8 ± 0.2 mm (range 6.1-9.0 mm); FW 4.3 ± 0.1 mm; PA angle 32.1 ± 2.1°; NT> 100; NW 7.0 ± 0.1 (n = 8). Ratio D/H 0.8; ratio FW/H 0.5.

Body.

The head and the neck are usually dark grey to grey. The sides and the posterior upper section of the foot are whitish. The foot is white and the sole is longitudinally divided into three areas. The central area is smooth, whereas the two lateral areas are equipped with bands of muscles that are roughly arranged in a chevron pattern. The mantle border is dark grey with five more or less developed lobes. The walls of the pallial cavity are colourless, without any stripes or spots. A strong pulmonary vein is visible. The jaw is odonthognatous and its shape is markedly arched. There are up to 25 smooth transverse ridges. The right ommatophoral retractor is independent from both penis and vagina.

Genital anatomy.

The albumen gland is short and as long as the sperm-oviduct. The prostatic part of the sperm-oviduct extends into a vas deferens that is approximately as long as the sperm-oviduct, which is inserting into the penial complex. The free oviduct is two times longer than the vagina. The duct of the bursa copulatrix is rather wide, slightly shorter than the penis, and uniform in diameter. It terminates in a roundish bursa copulatrix. The transition area between the duct and the bursa is very sharply delimited, abruptly widening and turning into the bursa. The spermatophore is unknown. One tuft of digitiform glands arises from the proximal part of the vagina. There are usually two rather wide glands that are approximately equally long and very rarely branched. A short and thin vaginal appendix arises from the wall of the vagina, just distal of the glandular tuft.

Very smooth, rather widely and irregularly spaced and little elevated pleats run longitudinally along the inner surface of the vagina, reaching into the genital atrium as far as the genital orifice. The atrium is rather wide. Its internal walls are equipped with large and soft pleats, running longitudinally towards the genital orifice. The penial flagellum is short, remarkably cylindrical and with a blunt apex. It is usually as long as the epiphallus. Its internal walls are equipped with a digitiform papilla that originates at the proximal end of the flagellum and which is orientated towards the penial papilla. The epiphallus is approximately half as long as the penis. Its internal walls are usually equipped with two to three longitudinal pleats. These pleats are arranged more or less “metameric”.

The retractor muscle is large, strong and is of variable length. The penis lacks any muscular or glandular sheath. It is thick-walled and approximately four times longer than the flagellum. It is cylindrical and slightly swollen in its proximal portion. The inner walls of the penis are equipped with a large longitudinal, fleshy, and smooth pleat, running from the penial papilla almost as far as the atrium. Some minor, smooth, longitudinal pleats are usually also present. The penial papilla is short but somewhat bulky. Its surface is smooth, with the opening emerging apically; its channel is rather narrow. The inner lumen of the penial papilla is filled with a spongy and sturdy tissue, which directly connects with the walls of the epiphallus. The longitudinal section of the penial papilla shows that its walls are the continuation of the penial walls that abruptly bend inward. See Figs 103-111.

Ecology.

Wollastonia turricula is found under volcanic rocks scattered on grassland in open fields.

Distribution.

Restricted to the slopes and plateau of the islet Ilhéu de Cima, off the southeastern coast of Porto Santo. The species occupies an area of less than two square kilometres (Fig. 112). The form pererosa of W. turricula is known to occur on the steep slopes at lower elevations of the islet Ilhéu de Cima.

Comparison and comments.

Wollastonia turricula is easily distinguishable from all the species belonging to either Hystricella or Wollastonia gen. n. by its peculiarly turreted shell and genital features. The anatomical and genital features of the species, under the name Ochtephila turricula , have previously been thoroughly described by Watson (1923), nevertheless Watson’s study limited its observations mostly to the external features of the genital system. Unfortunately, except for some drawings presented by Mandahl-Barth (1950), no additional information on the genital anatomy was published until now. Watson’s (1923) description, despite being thorough and accurate, sometimes gives a wrong impression of what the author observed. On p. 289 the author describes "three small finger-shaped processes" pointing out that "the shortest of the three is usually less than half the length of the others". He considered all these three processes "homologous with the so called mucous glands found in so many of the Helicidae ". Watson considered also the vaginal appendix as a gland that is probably an apomorphic state of the stylommatophores. He also wrongly considered the "conspicuous hemispherical swelling" on the outer side of the vagina to be "doubtless a degenerate dart-sac". It is known that the dart sac can assume such a “swollen” appearance, as for example in the genus Cernuella , but its inner structure shows a totally different arrangement compared to that found in W. turricula (see Giusti et al. 1995: 445). Watson also described the internal ornamentation of the penis as “smooth”, not detecting the main fleshy pleat and its surrounding secondary small pleats. Nevertheless, Watsons’ (1923) description as a whole is thorough and accurate, including also interesting notes about the histology of the tissues. This kind of anatomical description was very rare at the time, where conchological features were still considered as the most important taxonomical characters in land snail systematics.

Taxonomic remarks.

After its description, the taxon Helix turricula var. pererosa Wollaston, 1878 was mostly ignored by subsequent authors, except by Mandahl-Barth (1950) who treated it as a subspecies of W. turricula . Three syntypes of Helix turricula var. pererosa Wollaston (see Figs 112-114) could be traced at the Exeter Museum (coll n°EXEMS-1720-1909-d39-74). The preservation of the specimens clearly indicates that they were collected alive and not as subfossils. Following a careful morphological evaluation and a comparison with recent and subfossil specimens (Fig. 115), no substantial morphological differences could be detected with regard to the shell morphology, both concerning its micro- and macroscopic features (microsculpture, overall shape, keels, dimensions). Therefore, we treat it here as just a form of Wollastonia turricula and propose the name Helix turricula var. pererosa Wollaston, 1878 as a junior synonym of Wollastonia turricula . Pettitt (1977) reports on significant changes in the shell shape of W. turricula after the construction of the lighthouse on the islet Ilhéu de Cima after 1900. However, that observation may be based on material collected prior to the construction works and therefore may have contained more specimens of the form pererosa because the top of the islet was only easily accessible after the construction of the stairs to the lighthouse and therefore collecting probably was carried out nearer to the coast where the pererosa form predominates.

Status and conservation.

According to Seddon (2011e) the species is Vulnerable (VU). In our opinion, however, it should be regarded as Critically Endangered (CR B1a, b(ii, v), 2a, b(ii, v)) because the extent of occurrence and the area of occupancy of the species is less than 1 km2 and although Watson (1923) reported the species to "occur in considerable numbers" on Ilheu de Cima, observations made during the 1980s (KG) showed that the species is considerably less frequent than in the past, probably as the result of a decline of habitat quality as a consequence of grazing by goats or other unknown reasons (see also Seddon (2008: 80)). Moreover, living specimens were only reported from the area around the top plateau of Ilheu de Cima, i.e., at a single location (Fig. 117).