Wollastonia oxytropis (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 : 58-59

Wollastonia oxytropis (R. T. Lowe, 1831) comb. n. Figs 183-187, 188-194, 195

List of synonyms.

1831 Helix oxytropis R. T. Lowe: 57, pl. 6 fig. 18.

1846 Helix oxytropis - L. Pfeiffer: 142, pl. 91 figs 12-13.

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

1854 Helix oxytropis - Reeve in Reeve 1851-1854: pl. 138 fig. 868.

1854 Helix (Ochthphila) oxytropis - Albers: 37, pl. 9 figs 8-10.

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

1867 Helix (Octephila) oxytropis - Paiva: 46.

1878 Helix (Hystricella) oxytropis - Wollaston: 167-168.

1888 Helix oxytropis - Tryon in Tryon and [Pilsbry] 1888: 33, pl. 7 fig. 92.

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

1931 Geomitra (Actinella) oxytropis - Nobre: pl. 2 fig. 3.

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

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

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

2006 Discula oxytropis - Cameron et al.: 40 [partim].

2008 Hystricella oxytropis - Seddon: 79, map 180.

2009 Hystricella oxytropis oxytropis - Groh et al.: 21, fig. 26.

2011 Hystricella oxytropis - Seddon: e.T6728A12801442.

Type material.

NHM 1968.546, lectotype, (herewith designated), from loc. typ., ex coll. R. T. Lowe; NHM 1948.7.8.12/1 paralectotype, from loc. typ., ex coll. R. T. Lowe. See Fig. 183 for the original figure of Helix oxytropis R. T. Lowe, 1831 from Lowe (1831: pl. 6 fig. 18) and Figs 184-185 for the lectotype/paralectotype of Helix oxytropis R. T. Lowe, 1831 (Photo: P. Crabb, NHM).

Further material examined.

All from Porto Santo, CGK/1, CMN/1, Pico do Maçarico, under stones close to the top, 33°04'00"N / 16°18'17"W, 200 m, leg. K. Groh & J. Hemmen, Jul. 10 1983; CKG/2, Pico do Maçarico, under stones close to the top, 33°04'00"N / 16°18'17"W, 250-285 m, leg. K. Groh & J. Hemmen, Jul. 10 1983; CGK/2, CMN/1, Pico Novalido, W of Pico do Concelho, under stones, 33°04'43"N / 16°18'19"W, 185 m, leg. K. Groh & J. Hemmen, Jun. 29 1983; CGK/5, Pico do Concelho, SW slopes, under stones, 33°04'37"N / 16°17'47"W, 200-230 m, leg. K. Groh & J. Hemmen, Jun. 29 1983; CKG/2, slope of the Pico do Maçarico from Serra de Fora via Casas Velhas, 33°04'05"N / 16°18'35"W, 100-200 m, leg. K. Groh & J. Hemmen, Jul. 10 1983; CKG/5, Pico do Baixo, W slope, 33°03'45"N / 16°17'58"W, 150-210 m, leg. K. Groh & J. Hemmen, Jun. 9 1983; CWDM/25, ridge of Pico do Concelho towards E, under stones in grassland, 33°04'42"N / 16°17'56"W, 270 m, leg. W. De Mattia & J. Macor, May 18 2015; CFW 11153/<10, Pico do Concelho, ridge W of the summit, 33°04'43"N / 16°18'07"W, 220 m, leg. F. Walther, Apr. 3 2017; ANSP H 11846/10, CMN/2, Pico do Concelho, S slope, 33°04'41"N / 16°17'57"W, 280 m, leg. J. Gerber, K. Groh & J. Hemmen, Aug. 12 1985; ANSP H 11845/3, Pico do Concelho, W slope, 33°04'43"N / 16°18'04"W, 250 m, leg. K. Groh & J. Hemmen, Jun. 29 1983; ANSP H 11848/12, Pico Malhada, NW slope, 33°04'00"N / 16°18'02"W, 120 m, leg. K. Groh & J. Hemmen, Jul. 7 1983; ANSP H 11851/12, Pico do Macaricos, 33°03'58"N / 16°18'13"W, 230 m, leg. K. Groh & J. Hemmen, Jul. 10 1983; ANSP H 11850/3, Pico do Maçarico, SE slope, 33°03'57"N / 16°18'11"W, 220 m, leg. J. & C. Hemmen, Jan. 8 1981; ANSP H 11849/7, Pico do Concelho, SW slope, 33°04'42"N / 16°17'51"W, 200 m, leg. K. Groh & J. Hemmen, Jun. 29 1983; ANSP H 11849/14, approx. 0.5 km S Serra de Dentro, 33°04'44"N / 16°18'26"W, 125 m, leg. J. & C. Hemmen, Jan. 6 1981; ANSP H 11852/9, Pico do Maçarico, NE slope, 33°03'58"N / 16°18'09"W, 210 m, leg. K. Groh & J. Hemmen, Jul. 10 1983; ANSP H 11847/11, Pico do Baixo, 33°03'45"N / 16°17'57"W, 150 m, leg. K. Groh & J. Hemmen, Jul. 9 1983; ZMH 24293/2, Porto Santo, without exact locality data, ex coll. Altonaer Museum; ZMH 24294/1, Porto Santo, without exact locality data, ex coll. Altonaer Museum, ex coll. O. Semper, ex coll. Dohrn.

Locus typicus.

Hab. in collibus maritimis Portus Sti.

Original description.

From Lowe 1831: H. testa depresso-conoidea, supra planulata, perforata, carinata, tota scabra, fusca, sub-fasciata: spira depresso-conica; sutura distincta; anfractibus planiusculis; ultimi carina acuta, distinctissima, supra marginata sc. exarata vel sulco expressa; omnibus distinctissime confertim granulatis, asperis: umbilico minimo, sub-spirali, aperto: apertura rotundata; peristomate continuo, circinato, disjuncto, reflexo. Axis 2 ¼ lin. Diam. 4. Anfr. 6 ½.

Shell.

The shell is dextral and hairless. Its shape is rather flattened, almost discoidal, with shallow sutures. The protoconch is brownish with 2-2.3 whorls. It is almost smooth along the first whorl and shows fine radial striae along its remaining portion. The teleoconch has from 3.3 to 3.8 rapidly increasing whorls. It is violet-dark brown with brick red and/or dark violet shades. The dark areas of the shells are mottled with more or less brown to whitish areas, usually arranged longitudinally and slightly slanting. No band pattern is visible along the upper whorls. On the lower part of the last whorl two dark bands are visible that can be more or less broad. The peripheral band is usually broader, even if often rather blurred. In some specimens, the two bands merge together and form a single broad, dark band. The area around the umbilicus is the lightest in colour. The teleoconch whorls are rather flat, with shallow sutures and without a visible keel. The body whorl shows a strong, single keel that sometimes even bends slightly downwards. This keel is of the same colour as the remaining shell and its ornamentation pattern is also not markedly different from that of the rest of the shell’s surface. Contrary to most other Hystricella and Wollastonia species, the keel does not have the appearance of a rough chord. The surface of the teleoconch is ornamented with very fine, irregularly spaced growth lines and regularly arranged, very densely set small tubercles. The last whorl is usually large, contributing approximately 50% to the total shell height and descending near the aperture. The umbilicus is open, eccentric, and measures approximately 10% of the maximum shell diameter. The aperture is elliptical, with a faint thickening along the columellar portion of the stoma. This thickening can also extend as far the parietal side of the aperture. The peristome is continuous, thin, slightly reflected, with the columellar margin somewhat thicker and more reflected (see also Figs 186-187).

Measurements.

D 6.8 ± 0.2 mm (range 7.5-8.0 mm); H 4.9 ± 0.4 mm (range 4.4-5.5 mm); FW 2.7 ± 0.2 mm (range 2.3-3.0 mm); PA 35.8 ± 6.9° (range 33.6-39.3°); DU 0.5 ± 0.05 mm (range 0.4-0.6 mm); NT 89 ± 14 (range 96-61); NW 5.6 ± 0.3 (range 5.3-5.9) (n = 25). Ratio D/H 1.4; ratio FW/H 0.6.

Body.

As in the genus description. Wollastonia oxytropis tends however, to have an overall darker body colouration than the other Wollastonia species.

Genital anatomy.

The albumen gland is long and thin and is connected to an approximately twice as long sperm-oviduct. The thin vas deferens is roughly 1.5 times longer than the penial complex. The free oviduct is as long as the vagina. The duct of the bursa copulatrix is thin, approximately as long as the penial complex and uniform in diameter. It ends in a roundish bursa copulatrix. The transition area between the duct and the bursa itself is sharply delimited, with the duct 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 three 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. The internal walls of the vagina are smooth, as are those of the atrium. The atrium is relatively long and thin. The penial flagellum is very short, cylindrical, has a somewhat blunt to slightly pointed apex, and is usually much shorter than the epiphallus. The epiphallus is approximately as long to slightly longer than the penis. Its internal wall is equipped with irregular longitudinal pleats. The retractor muscle is rather large, strong and of variable length. The penis misses any muscular or glandular sheath. It is thick-walled, cylindrical, and slightly swollen at the level of the penial papilla. The inner walls of the penis are smooth. The penial papilla is small and it usually has a blunt shape. It has smooth external walls with the opening emerging apically. The channel of the penial papilla is thin and narrow. The inner lumen of the penial papilla is occupied by 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 188-194.

Ecology.

Wollastonia oxytropis is found under volcanic stones and rocks, in rock crevices and stone walls built in open, stony fields in sloping grasslands.

Distribution.

Wollastonia oxytropis has a quite small distributional range. It is known to live exclusively along the SE part of the main island Porto Santo: Pico do Baixo, Pico do Maçarico, Pico do Concelho and Pico do Novalido. These localities were confirmed by survey performed during the 1980's and 1990's (CKG, ANSP, Seddon 2008). During recent field surveys (WDM 2012, 2014, 2015, FW 2017) the species has been found living only along the ridge of Pico do Concelho despite careful searches at the above-mentioned localities. The known distribution is shown in Fig. 195.

Comparison and comments.

Wollastonia oxytropis is clearly distinguishable from all other species belonging to Hystricella and Wollastonia by the presence of only a single keel, the rather flattened, almost discoidal shell with very shallow sutures and the extremely short flagellum in relation to the epiphallus.

Taxonomic remarks.

Wollastonia oxytropis is somewhat unusual among the Wollastonia gen. n. species as its genital anatomy is more similar to that of the investigated Discula s. str. species than to that of the remaining Wollastonia gen. n. species. However, in the cox1 phylogeny (Fig. 5) the species is clearly embedded within the Wollastonia gen. n. clade indicating that the similarity in genital anatomy may be the result of convergence. We therefore include the species in Wollastonia gen. n. until more in depth phylogenetic analyses and morphological comparisons of the remaining geomitrinid genera will become available.

Status and conservation.

According to the current IUCN assessment ( Seddon 2011d) the species is considered Near Threatened (NT). Recent surveys indicate however that the species is clearly declining, both with regard to the distributional range and population size, probably as a result of a decline in habitat quality. The area of occupancy and extent of occurrence is approximately 4 km² and the species occurs at relatively few localities clustered in the upper parts of two hills in the south-eastern part of Porto Santo. Therefore, the species should be considered as Endangered (EN B1a, b(iii), 2a, b(iii)).