A new species of Drymaeus endemic from Currais Archipelago, Paraná, Brazil (Pulmonata, Bulimulidae)

The new bulimulid species, Drymaeus currais sp.  nov., is described based on shell and anatomical features. It is endemic of Guapirá Island, belonging to the Currais Archipelago, a small protected area off Paraná coast. The species is thus, based at least on endemicity, endangered. It has as closest species D. castilhensis, another endemic species of Castilho Island, ~70 km northwards. Its main exclusivities are a banded shell (except for periumbilical area); a ureter ~1/3 opened (furrow); an external anus; a slightly different buccal and intestinal arrangement; a penis lacking internal chambers; a small receptacle with a genital appendix. Zoobank Register: urn:lsid:zoobank.org:pub:25B25A8B-CED0-4284-A799-5383998BE481. Key-Words. New species; Endemic; Endangered; Anatomy; Morphology; Taxonomy.


INTRODUCTION
The taxonomy of land snails from southwestern Atlantic islands has been investigated in a long-term project. Both remote oceanic island (about a thousand km off ) as well as islands located closer to the Brazilian coast (about 20-30 km off ) have shown a high degree of endemicity of the land snail species, something close to 100%. The latest paper of this project described three new bulimulids, each one endemic from an island off the São Paulo coast -Castilho, Queimada Pequena and Alcatrazes (Simone & Amaral, 2018).
Paraná is the neighboring state south from São Paulo, and also has some oceanic islands. One of them is the Currais Archipelago (Fig. 1). The Archipelago is located in the central portion of the Paraná coast (25°44′07.74″S, 48°21′58.12″W) approximately six nautical miles from the municipality of Pontal do Paraná, and consists of a group of three small rocky islets. Grapirá Island represents 81% of the total area of the archipelago, estimated in 73,534 m². From the rest of the area, 19% includes two small rocks: the first, with 7,748 m², and the second, on the west side of the archipelago, with 6,249 m² (Borzone et al., 1999). The archipelago belongs to the National Marine Park of the Currais Islands, a marine protected area of 1,357.7 hectares (ICMBio, 2020).
The Currais Islands come from a Precambrian crystalline rocky outcrop of the so-called Coastal Granitoid Belt, presenting a lithology formed by intrusive and migmatite granites. The submerged portion adjacent to these is characterized by sandy marine sedimentation with predominantly sand granulation thin or medium (0.125-0.5 mm) and inclination less than 2º (Bigarella et al., 1965).
The climate of the coastal plain of Paraná, where the Currais archipelago is located, is Cfa type (Humid Subtropical Climate -Mesothermal), with an average of the warmest month above 22°C and in the coldest month below 18°C, with no defined dry season, hot summer and less frequent frosts (Vanhoni & Mendonça, 2008).
The vegetation formation of the archipelago is of the Dense Ombrophilous Forest of Low Lands type, with pioneer rupicolous formations of marine influence along the rocky shores. This phytogeographic unit is characterized by indisputable environmental importance, with high biological diversity and a large number of endemism. It presents a very typical floristic and structural composition composed of different communities along the altitude gradient and the pioneer formations, ranging from herbaceous vegetation to tree remainings rich in epiphytes (Roderjan et al., 2002).
Its main island, Guapirá, is a little larger than a football field; it is the tip of a small mountain cov-ered by a luxuriant Atlantic Rainforest fragment. In that island, a population of a pretty land snail occurs, initially identified as Drymaeus castilhensis Simone & Amaral, 2018, by its similar shell features, a species so far endemic of the Castilho Island, separated by ~70 km of ocean northwards from Currais. However, the complementary anatomical study revealed important anatomical differences, allowing the specific separation. The new entity is formally described herein.
The description of the new species endemic from a relatively small island reinforces the necessity of environmental protection of the Currais Archipelago, another important issue that merits proper emphasis.
The genus Drymaeus has about 300 species, 49 of them in Brazil (Simone, 2006;Birckolz et al., 2016). It is widespread from south of North America, Caribbean islands, Central America, up to central Argentina along almost the entire South America, including the Andes and all mainland forests. Its distinction with other bulimulid genera, such as Naesiotus Albers, 1850, Mesembrinus Albers, 1850, Leiostracus Albers, 1850, is not straightforward, and some degree of overlapping exists. Normally, Drymaeus have bulimuliform shells with rich color and delicately reticulated protoconch.

MATERIAL AND METHODS
The specimens were collected in duly authorized projects (SISBIO license number 47215-3), as the region is protected; a complete list of examined material follows the species description. The samples were fixed unrelaxed in 75% EtOH. The dissections were performed by standard techniques, with the specimens immersed in alcohol, examined in dissecting stereomicroscopes. All drawings were done with the aid of a camera lucida, and most drawing normally are based on several specimens. Photos of all dissecting steps were made by digital camera coupled to the microscope. SEM examinations were performed in a Zeiss device of the Laboratory of Electronic Microscopy of the Museu de Zoologia da Universidade de São Paulo -MZSP. This institution also houses most of type material.
Diagnosis: shell conical, aperture ample, weakly deflected. Color white-cream, mostly with strong axial, dark brown spots; peri-umbilical area lacking spots; some rare specimens uniformly yellowish beige. Secondary ureter closed only in posterior 2/3, furrow-like in third preceding pneumostome. Pulmonary vases particularly dense, mainly on third preceding pneumostome. Anus external to pneumostome, opened directly outside. Aperture of salivary glands lateral in middle level of buccal cavity. Intrinsic pair of odontophore muscles m7 originating in cartilages close to m6; presence of odontophore pairs m1a and m3. Sigmoid intestinal loop relatively short. Penis slender and long, lacking clear inner chambers. Inner spermoduct of spermoviduct protected by tall fold. Seminal receptacle small, with additional elongated diverticulum called genital appendix. Albumen gland duct single, elongated. Pleural ganglia inconspicuous.
Head-foot: of usual shape. Color uniformly clear. Columellar muscle thick, 1.8 whorls in length.
Mantle organs: (Figs. 23-26) mantle border thick, lacking pigments. Pneumostome (pn) protected by ventral, right simple flap (mf ), with ~1/5 of aperture length. Dorsal fold about double of ventral flap, ~1.5-times longer. Pneumostome (pn) ~1/9 of aperture length, bearing air entrance, urinary escape ( Fig. 24: ua) in left-anterior side ( Fig. 23: pn), and anus in right-posterior side, separated by transverse fold (Fig. 23: an). Lung of 1.5 whorls in length, ~tice longer than wide. Pulmonary vessels conspicuous all along right side (Fig. 24), mostly bearing transverse, rather perpendicular vessels, clustered, sometimes bifurcating or anastomosing; in left side of pulmonary vein (cv), visible vessels only in anterior third, occupying right ~half of this area, constituted by transverse vessels of similar fashion as right side, but inserting in longitudinal vessel (Fig. 24: vp), in such anterior end converge with anterior end of pulmonary vessel as part of collar vessel ( Fig. 26: co). Remaining regions of lung almost smooth, with imbricated vessels of difficult visualization. Pulmonary vein (cv) running longitudinally between middle and right thirds of pallial cavity roof, somewhat equidistant from rectum all along its length. Reno-pericardial area triangular, located posteriorly at middle level of posterior end, occupying ~25% of cavity length and ~70% of its width (details below). Rectum (rt) and ureter (ur) narrow, running along right edge. Urinary aperture very elongated (Figs. 24,13: ua), occupying ~1/3 of ureter length; its posterior end slightly rounded, its anterior end just left from anus, T-shaped, being its left branch longer and anteriorly protected by special fold (Fig. 26: pn).
Circulatory and excretory systems: (Figs. 13,24,25) Pericardium (pc) ~3-times as long as wide, located longitudinally between middle and left thirds of posterior end of pallial roof; occupying ~5% of lung area. Auricle (au) located anteriorly, as continuation from pulmonary vein (cv), slightly larger than ventricle (ve). Kidney (ki) simple, mostly solid, dorso-ventrally flattened; size reported above; somewhat triangular, width ~2/3 of length; inner lobe constituted by longitudinal, tall folds converging anteriorly to middle axis of structure (Fig. 13). Nephropore small, longitudinal slit in anterior-left corner, turned right (Figs. 24,25: ne). Primary and secondary ureter complete and closed (tubular); primary ureter (up) lying on right edge of kidney towards posterior and right, after forming strong curve, running afterwards anteriorly, as secondary ureter (ur) along entire left edge of rectum, except for longitudinal urinary aperture of ~1/3 of its length (ua) (details above).
Radula (Figs. 14-22) as long as odontophore; with rachidian teeth, and ~55 pairs of lateral teeth; no clear distinction between lateral and marginal teeth (Figs. 18,19,21,22); all teeth with relative long and flattened base, located closely from neighboring rows; central set of cusps rather small, located in anterior end of base. Rachidian tooth (Figs. 15, 16,  of basal cusps with ~1/5 of central cusp's size (Fig. 16). Lateral teeth similar to rachidian, except in being ~twice larger, asymmetrical, arched towards lateral region, cutting edge ~1.5-times larger than that of rachidian; lateral teeth gradually weakly decreasing towards lateral; set of cusps with ~1/2 of length of base; central cusp bluntly pointed; basal cusps strongly asymmetrical, outer basal cusp almost as large as central cusp in more central teeth, almost originating from base (Fig. 16), gradually becoming smaller and sometimes separated from central cusp (Fig. 15); inner cusp ~3-4-times smaller than lateral cusp. Marginal teeth starting with no clear boundary with lateral teeth; shaped similarly to lateral teeth, except for being weakly smaller and with set of cusps broader and slightly less pointed (21)(22); inner basal cusp gradually becoming as large as outer basal cusp and bifid, dividing in two cusps (Figs. 17, 21, 22); teeth becoming very narrow in margins (Fig. 19). Each radular row slightly arched disposed from both sides from rachidian (Fig. 14).
Central nervous system: (Figs. 35,36) cerebral ganglia located dorsally in middle level of buccal mass, pedal ganglia located more posteriorly. Pair of cerebral ganglia (ce) widely fused with each other; cerebral commissure invisible; each ganglion about as wide as adjacent esophageal section (Fig. 25: nr); several wide nerves originating in cerebral antero-lateral region. No clear cerebral node or gland. Two pairs of parallel connectives between cerebral ganglia and pedal ganglia. Pair of pedal ganglia (pp)  Simone, L.R.L. et al.: A new species of Drymaeus from Paraná, Brazil Pap. Avulsos Zool., 2020;v.60: e20206057 9/11 forming single mass located opposite to cerebral ganglia, slightly larger sized than cerebral ganglia. No differentiable individual pedal ganglion detectable.
Habitat: The animals were found in a shaded area, inhabiting both the trunks and the abaxial part of the leaves of the tree vegetation of the Ombrophiles Dense Forest that covers the island. They were also located in the bromeliads of the rocky shores that are part of the pioneer rupicolous vegetation.

DISCUSSION
The closest species from Drymaeus currais sp. nov., undoubtedly, are the also insular species D. castilhensis and D. micropyrus Simone & Amaral, 2018. As informed in the 'Introduction' , the shell of D. currais sp. nov. is practically indistinguishable from that of D. castilhensis, in a first tentative identification. In this aspect, the same taxonomical comparisons of both Simone & Amaral's (2018) species to other congeneric species can be herein applied. The present discussion is, thus, focused on the distinction amongst these three species.
The distance between the Castilho Island, location of occurrence of D. castilhensis, and the Currais Archipelago, location of occurrence of D. currais sp. nov., is of about 70 km of sheer ocean. This distance certainly precludes any kind of gene flow. A possible transportation via oceanic birds sounds implausible, as the snails are quite large, and would hardly resist a 70 km flight of a bird. Much closer is the mainland coast (~5 km for Currais, ~7 km for Castilho), and it is possible to theorize that a continental population can genetically connect both insular populations. However, such kind of Drymaeus is unknown in the continental coastal stretch between São Paulo and Paraná. Queimada Pequena island, location of occurrence of D. micropyrus, is further 30 km norther.
The description above includes also the effort in distinguishing D. currais sp. nov. from D. castilhensis, as it is mostly comparative, mainly in the anatomical part. Thus, a complete distinction between the two species are better explained along the description. In the present discussion, the more important distinctions are reported, as follows. The shell protoconch of D. currais sp. nov. (Fig. 9) is slightly taller and more acuminated than those of D. castilhensis and D. micropyrus (Simone & Amaral, 2018, figs. 8, 10); additionally, the protoconch of D. currais sp. nov. is ~60% smaller than that of D. micropyrus. In average, the ventral region of the last whorl of D. currais sp. nov., mainly in the region above peristome, is slightly broader than those of the other two species; this is a pa-rameter difficult to measure, but the peristome of D. currais sp. nov. is approximately as wide as the distance between the superior implantation of outer lip and the right edge of the last whorl profile (Figs. 2, 5, 7), while in the other two species, this parameter is ~80%. The shell color patterns of D. currais sp. nov. are really indistinguishable from D. castilhensis, however it presents the same differences of D. micropyrus than those reported for D. castilhensis in the original description.
Anatomically, Drymaeus currais sp. nov. differs from D. castilhensis mainly by: more elongated aperture of the ureter, ~1/3 of the ureter length (Figs. 24, 26), against ~1/3 of D. castilhensis; much more richness of pulmonary vessels, mainly in right side of the pulmonary vein (Fig. 24), these vessels are much less developed in D. castilhensis; salivary glands more anteriorized located, with the respective ducts much shorter ( Fig. 25: sg, sd); single duct to anterior lobe of the digestive gland ( Fig. 25: dd), which is bifid, each branch connecting in different sides of the adjacent intestinal loop in D. castilhensis; intestinal loops much shorter at visceral mass (Fig. 25: in); jaw plate with less developed medial narrowing ( Fig. 10: jw); odontophore with pairs m1a and m3, both absent in D. castilhensis; genital carrefour area with genital appendix ( Fig. 32: ga); duct of the albumen gland single (Fig. 32: ad), while it is double in D. castilhensis; epiphallus internal folds more uniform sized, while D. castilhensis has a strong large longitudinal fold; separation of the vas deferens much more posterior (Fig. 31: vd), while that of D. castilhensis is much more anteriorized (Simone & Amaral, 2018: fig. 50). This is a considerable anatomical amount of differences for so close related species. From D. micropyrus, D. currais sp. nov. differs in the same characters as those reported by Simone & Amaral (2018) for D. castilhensis, mainly in the separation of the duct of the albumen gland and insertion of seminal receptacle (Fig. 32), and by tall longitudinal fold separating masculine from feminine regions of the spermoviduct ( Fig. 33: sp).
As the taxonomy of the bulimulids, Drymaeus in particular, is practically only based on shell characters, several cryptic species may exist in the genus. The present study is an example, as two populations with almost indistinguishable shells hide higher anatomical differences, which can be interpreted as different species. The extra-shell characters, thus, must be explored as much as possible in these organisms.