Drouetia Gude, 1911

De Frias Martins, António M., Brito, Carlos P. & Backeljau, Thierry, 2013, Oxychilus (Drouetia) viridescens (Gastropoda: Pulmonata: Oxychilidae), a new species from Santa Maria, Açores, and a review of the subgenus, Zootaxa 3619 (3), pp. 343-368 : 361-364

Reviewing Drouetia Gude, 1911 and Atlantoxychilus Riedel, 1964

The genus with the highest number of endemic taxa in the Azorean biota is the molluscan Oxychilus , of which the subgenus Drouetia accounts for 8 of the 15 hitherto described endemic species of that genus. However, Drouetia was first monotypic (Gude 1911), for its type species, Helix atlantica , was considered to live throughout most islands of the Azores (Morelet 1860). It was only through Riedel’s (1964) anatomical research that the diversity of Drouetia started to be noticed, and Martins (2005) has provided evidence that the number of known species remains understated. Besides the three species from Santa Maria sufficiently dealt with above, five more species are known: two from São Miguel, O. (D.) atlanticus and O. (D.) batalhanus de Winter, 1989; two from Terceira, O. (D.) miceui Martins, 1989 and O. (D.) furtadoi ; one from Faial, O.(D.) minor Riedel, 1964 . Atlantoxychilus is represented by one, already mentioned species: O. (A.) spectabilis .

Oxychilus (Drouetia) atlanticus ( Fig. 18 C, 19, 20A). The history of this taxon has been dealt with above (see Remarks). Martins (1991) first reported the anatomical variability of O. (D.) atlanticus throughout São Miguel and, although calling attention to variability as an artifact of preservation, recognized the possibility of additional species, namely Riedel’s (1964) “small form” and the population of Sete Cidades. Nevertheless, Martins’ (2005) extended analysis interpreted those differences as allotopic, demic variability. However, further anatomical and morphometric research has revealed syntopic variability, with different shell and genitalia patterns existing sympatrically, thus suggesting the existence of various taxonomic units in São Miguel (Martins et al. 2010), the description of which is presently under way. Oxychilus (D.) atlanticus needed, thus, to be unequivocally characterized. To this end, a neotype was proposed so to restrict O. (D.) atlanticus to the large shell phenotype living in Sete Cidades, São Miguel (ICZN Case 3553; Martins et al. 2011). However, this proposal is no longer needed, since the recent discovery of Drouët´s collection of Azorean material, with specimens from São Miguel, provided a suitable lectotype for Helix atlantica (MJSD.2012.CO.68 a; Fig. 19 ). The specimen selected is the largest of a lot of 48 (diameter 7.8 mm; height, 4.8 mm; number of whorls, 6) and conforms with the measurements given in the original description (maximum diameter, 8 mm; height, 5 mm; Morelet & Drouët 1857). Due to the taxonomic and morphological complexity of Drouetia in São Miguel and the importance of anatomy and locality for species identification (Martins 1991, 2005), the type locality for Helix atlantica Morelet & Drouët is herein restricted to Caldeira das Sete Cidades. Indistinguishable from the following species on the basis of shell morphology alone, O. (D.) atlanticus has a darker border of the mantle and the foot sole is yellowish; however, it is readily identified anatomically, namely by the long epiphallus, the long and narrow bursa duct and large bursa, and, inside the penis, the reticulate ornamentation on the penial caecum and around the epiphallic pore.

Oxychilus (D.) batalhanus de Winter, 1989 ( Fig. 18 D, 20B). Conchologically indistinguishable from the previous species, O. (D.) batalhanus was proposed on the basis of the morphology of the penial complex (de Winter 1989). Martins (1991) showed that the proportions of various structures of the penial complex, namely the penial caecum, can change as an artefact of preservation methods and, therefore, are by themselves unreliable diagnostic characters. For that reason O. (D.) batalhanus was considered a junior synonym of O. (D.) atlanticus (Martins 2005) . Recent research based mostly on the internal morphology of the penis (Martins et al. 2010) has provided evidence for the existence of various taxonomic units in São Miguel; restriction of O. (D.) atlanticus to the anatomically different Sete Cidades population restores the validity of O. (D.) batalhanus . Although very variable, when compared with the previous species O. (D.) batalhanus shows a lighter blue border of the mantle and the foot is pinkish to orange, sometimes greenish; it is diagnosed by the short vagina, the membranous proximal penis with weak crests radiating from the epiphallic pore, the strongly muscular distal penis with strong pilasters inside. Oxychilus (D.) batalhanus is distributed throughout the entire island of São Miguel.

Oxychilus (D.) miceui Martins, 1989 ( Figs. 18 E, 21A). This species lives on the mountains of Terceira and is characterized by the yellow to whitish mantle spotted with small brown to blackish patches, contrasting with the dark-blue mantle border and neck, fading to light-blue toward the foot. The shell has a depressed spire, the last whorl a quadrangular profile, the aperture is slightly wider than that of the following species. Anatomically this species is characterized by a long, convoluted oviduct and moderately long vagina, a membranous proximal penis and penial caecum cumulatively as long as the muscular distal penis, both units usually separated by a constriction.

Oxychilus (D.) furtadoi Martins, 1989 ( Figs. 18 F, 21B). This species lives at lower altitude around the town of Angra do Heroísmo, Terceira. Conchologically similar to O. (D.) miceui , it has a slightly narrower aperture. The mantle has a greenish-brown background spotted with sparse, small whitish patches, the mantle border and neck light-blue, turning pinkish toward the foot. The reproductive anatomy is characterized by a long, narrow vagina, a short, membranous proximal penis and penial caecum, a long, narrow, muscular distal penis and an equally long penial sheath; the epiphallus is long, the distal third connected to the distal penis by muscular strands.

Oxychilus (D.) minor Riedel, 1964 ( Figs. 18 G, 21C). This species was first referred by Morelet (1860) as variety “β minor ”, and it was Riedel (1964) who considered it a discrete taxon, attributing authorship and date to Morelet (1860). Bank et al. (2002), however, interpreted Morelet’s word “ minor ” not as a name but as part of the description, thus attributing authorship and date to Riedel (1964). The animal of O. (D.) minor is characteristically pink, the mantle mottled with white patches and rare dark spots, posterior tentacles dark-blue becoming lighter toward the base. The shell has a depressed spire and the aperture is somewhat wide. The most peculiar anatomic feature is the stout, strongly muscular penis without noticeable constriction, with strong pilasters running back to the penial caecum.

Oxychilus (Atlantoxychilus) spectabilis (Milne-Edwards, 1885) ( Fig. 18 H). Hausdorf (1993) considered Helix atlantica var. spectabilis Morelet, 1860 to be a primary homonym of Helix spectabilis Pfeiffer, 1844 , and introduced accordingly the new name Oxchilus ( Atlantoxychilus ) riedeli. However, Bank et al (2002) considered Hausdorf’s (1993) nomenclatorial action invalid, for Morelet’s (1860) indication of a “γ var. spectabilis ” did not constitute attribution of a name to the variety, the word “ spectabilis ” instead being part of the description of variety γ. The name was validly introduced by Milne-Edwards (1885) as Hyalinia spectabilis , which is not preoccupied. Some aspects of this species were already dealt with, and only a brief morphological characterization will be added. The mantle is brown, crossed by elongated, irregular golden-brown blotches; border of mantle light-brown; neck dark-brown, sharply separated from the golden-brown foot which is surrounded by an intermittent brown rim.

Figures

FIGURE 18. Animals of species of Drouetia and Atlantoxychilus. A, Oxychilus (Drouetia) viridescens, Sta 7. B, Oxychilus (Drouetia) agostinhoi, Sta 7. C, Oxychilus (Drouetia) atlanticus (NHMUK 20100653), Sete Cidades, São Miguel. D, Oxychilus (Drouetia) batalhanus, Batalha, São Miguel (type locality). E, Oxychilus (Drouetia) miceui, paratype, Caldeira de Santa Bárbara, Terceira. F, Oxychilus (Drouetia) furtadoi: paratype, Fonte da Telha, Posto Santo, Terceira. G, Oxychilus (Drouetia) minor, Ribeirinha, Faial. H, Oxychilus (Atlantoxychilus) spectabilis, Sta 7.

FIGURE 19. Lectotype of Helix atlantica Morelet & Drouët, Muséum Jardin des Sciences de Dijon, France (MJSD. 2012. CO. 68 a), São Miguel. Scale bar = 1 mm.