Wollastonia klausgrohi De Mattia & Neiber

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 : 52-58

Wollastonia klausgrohi De Mattia & Neiber sp. n. Figs 168-170, 171-181, 182

Type material.

NMWC Z.2016.013.00003, holotype, from loc. typ., leg. W. De Mattia & J. Macor, May 27 2015; NMWC Z.2016.013.00004/4 PT, SMF 348932/4 PT, NHMW 112139/3 PT, CKG/3 PT, CWDM/8 PT, CMN/4 PT, from loc. typ., leg. W. De Mattia & J. Macor, May 24 2015; FW 11156/25 PT, CMN/10PT, ZMH 131209/10 PT, Casa Velhas, next to the W edge of the old quarry, 33°04'06"N / 16°18'51"W, 125 m, leg. F. Walther, Apr. 3 2017; CGK/3 PT, Portela, 33°03'58"N / 16°19'03"W, 146 m, leg. K. & C. Groh, Oct. 25 1980; ANSP H 11784/8 PT, approx. 200 m SE of Casas Velhas, 33°04'04"N / 16°18'47"W, 120 m, leg. J. & C. Hemmen & K. & C. Groh, Jul. 8 1983; ANSP H 11772/14 PT, approx. 50 m above Capela da Graça, 33°04'28"N 16°19'26"W, 165 m, leg. J. & C. Hemmen, Jan. 4 1981.

Locus typicus.

Casa Velhas, next to the W edge of the old quarry, under stones, 33°04'06"N / 16°18'52"W, 124 m.

Diagnosis.

Small Wollastonia species, with two well-developed keels on the body whorl, the upper slightly less distinct than the lower; shell relatively dark coloured (in comparison with W. jessicae ); internal walls of vagina, penis and genital atrium smooth, without folds.

Description of shell.

The shell is dextral and hairless. Its shape is conical and markedly scalariform, with deep sutures. The protoconch is completely dark brown with 1.5 to 2.5 whorls. It has fine radial striae starting from the first protoconch whorl; very few and scattered small tubercles may also be present on its last portion. The teleoconch has from 3.4 to 3.9 rapidly increasing whorls. It is dark brown, sometimes with dark violet shades. The dark areas of the shells are mottled with more or less light brown to whitish areas, usually arranged longitudinally and slightly slanting. In most specimens, the lighter areas tend to be more evident along the keel of the body whorl. No band pattern is visible along the upper whorls. On the lower part of the last whorl two dark bands are present. The inner band is usually thinner but more evident, whereas the outer band is usually weaker but broader. The area around the umbilicus is the lightest in colour. Some specimens clearly have two evident keels starting already from the second whorl of the teleoconch, with the upper keel being more distinct than the lower one. In other specimens only the upper keel is visible. The body whorl is equipped with two keels, with the lower, principal keel somewhat protruding and the upper much less distinct. The whorls are flat and form a ‘shoulder’ giving them an angular contour. The external surface has strong, clearly visible, irregularly spaced, growth lines. Irregularly disposed tubercles are present all over the teleoconch. The tubercles are usually small and scattered, usually whitish in colour. The tubercles are somewhat denser along the keels of the penultimate and last whorl, letting the keel(s) appear like a rough, whitish chord. The last whorl is rather large, contributing 60% to the total shell height and descending near the aperture. The umbilicus is open but very narrow, eccentric, and measures approximately 10% of the maximum shell diameter. The aperture is elliptical, with a faint thickening along its columellar portion. This thickening also extends as far as the parietal side of the aperture. The peristome is continuous and distinctly reflected (see Figs 168-170).

Measurements.

D 5.3 ± 0.2 mm (range 5.1-5.5 mm); H 4.0 ± 0.2 mm (range 3.8-4.2 mm); FW 2.5 ± 0.1 mm (range 2.4-2.6 mm); PA 58.0 ± 3.4° (range 52.8-60.4°); DU 0.5 ± 0.07 mm (range 0.4-0.6 mm); NT 57 ± 17 (range 46-77); NW 5.6 ± 0.1 (range 5.5-5.7) (n = 25). Ratio D/H 1.3; ratio FW/H 0.6.

Body.

The head and neck are usually dark grey. The sides and the posterior upper section of the foot are grey. The foot is light grey 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 ratio of the lateral and the dorsal lobes varies from specimen to specimen, also in the same population. In some specimens, one of these lobes (either lateral or dorsal) may be totally missing. The walls of the pallial cavity are colourless, without any stripes or spots. A strong pulmonary vein is visible. The jaw is odonthognatous and is very variable in shape, from almost straight to markedly arched. There are many smooth transverse ridges, ranging from 18 to 22 in number. The right ommatophoral retractor is independent from both penis and vagina.

Genitalia.

The albumen gland is long and connected to an approximately equally long sperm-oviduct that consists of a prostatic and a uterine portion. The prostatic part extends into a thin vas deferens that is approximately as long as the sperm-oviduct and inserts into the penial complex. The distal portion of the uterine part extends into the free oviduct, turning into a vagina at the level of the duct of the bursa copulatrix. The free oviduct is variable in length and can be as long as the vagina or also three times longer. The duct of the bursa copulatrix is usually thin, approximately as long as the penis and uniform in diameter. It terminates into a roundish bursa copulatrix. The transition area between the duct and the bursa is very 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 two glands that are approximately equally long and are never branched. A short and thin vaginal appendix arises from the wall of the vagina, just distal of the glandular tuft. The inner surface of the vagina is almost smooth. The atrium is usually moderately long and thin. Its internal walls are smooth. The penial complex consists of a flagellum, an epiphallus (which extends from insertion of the vas deferens to penial retractor muscle) and a penis that inserts into the 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 usually short. Its internal walls are also completely smooth. The retractor muscle is moderately large, strong and variable in length. The penis lacks any muscular or glandular sheath. It is thick-walled and approximately three to four times longer than the flagellum. It is usually cylindrical but sometimes slightly swollen and partially folded up. Sometimes, a thin sheath made of light connective tissue envelopes the distal folded part of the penis. The inner walls of the penis are smooth. The penial papilla is usually small, sometimes swollen at its base, reaching 1/8 to 1/10 of the total length of the penis and is conical in shape. It has smooth external walls, with the opening emerging apically. The channel of the penial papilla is thin and narrow, with somewhat fringed internal walls. The inner lumen of the penial papilla is occupied by a spongy and sturdy tissue, which directly connects with the walls of the epiphallus. As all the previous species, the longitudinal section of the penial papilla shows that its walls are the continuation of the penial walls that abruptly bend inward (see Figs 171-181).

Distribution.

Wollastonia klausgrohi sp. n. is found along the Casa Velhas area, just W of an abandoned quarry. The W tip of the quarry (currently not exploited at this part) is located only 10 meters from the type locality. Casas Velhas is located along the road n° 233 in direction of Zimbreiro, 340 m ENE from the Miradouro de Portela, E of Vila Baleira. The species has also been collected at Portela, ca. 300 m WSW of the loc. typ., Capela da Graça and 200 m SE of the type locality. The species seems to occupy less than 2,000 m2. For the distribution see Fig. 182.

Ecology.

Wollastonia klausgrohi sp. n. is commonly found under volcanic rocks of a low stone wall built in an open field in a sloping grassland. The specimens directly aestivate on the lower surfaces of the rocks, frequently forming clusters of individuals attached one to another.

Etymology.

Named for our co-author, the German malacologist Klaus Groh from Bad Dürkheim to honour his contributions to the malacology of continental snails on the Mid-Atlantic islands.

Comparison and comments.

Wollastonia klausgrohi sp. n. has a shell similar to W. jessicae jessicae sp. n. but differs from that species by a last whorl that is always bicarinate, with the upper keel well-visible. The overall colour of the shell is constantly darker in W. klausgrohi sp. n. More important differences are found in the genital anatomy. The internal walls of the penis, atrium and vagina of W. klausgrohi sp. n. are completely smooth, without any pleating or folding. It also resembles H. bicarinata , which, however, always has a wider and shorter atrium and a shorter vagina. Molecular investigations revealed that W. klausgrohi sp. n. is rather closely related to the morphologically very distinct W. oxytropis , whereas W. jessicae sp. n. is closely related to W. leacockiana that occurs in the western part of Porto Santo. Altough W. klausgrohi sp. n. was not recovered as a monophyletic group in the phylogenetic analyses (Fig. 5), statistical support values are rather low, so that monophyly can also not be excluded. We assume that the resolution power of the used molecular markers is insufficient to separate W. klausgrohi sp. n. and W. oxytropis . However, both taxa can easily distinguished by size, shell shape, ornamentation and genital anatomy (Figs 168-181, 183-194) and therefore are separated as distinct species here. Their distribution areas partly overlap, so that we can currently not exclude mitochondrial introgression as an explanation for the observed pattern in the phylogenetic tree in Fig. 5. Another explanation could be incomplete lineage sorting/ancestral polymorphism assuming a relatively recent divergence of the two taxa. An approach using population genetic markers could help to resolve these issues, such an approach is, however, beyond the scope of the present investigation.

Status and conservation.

Because of the very restricted distribution area, the low number of known subpopulations (Fig. 182) and the probably very small population size as well as potential threats through tourism, goat grazing and especially ongoing quarrying, the species is regarded as Critically Endangered (CR B1a, b(iii), 2a, b(iii)) here.