Megalobulimus dryades, a new species from the Atlantic Forest in southeastern Brazil, and redescription of Megalobulimus gummatus (Gastropoda: Strophocheilidae)

Megalobulimus dryades sp. nov. is described from the Atlantic Forest in the Vale do Ribeira region, in the states of Paraná and São Paulo, S-SE Brazil, based on morphology. Representatives of the new species with white peristome and glossy periostracum have been misidentified as Megalobulimus gummatus (Hidalgo, 1870) since the 19th Century. The true M.  gummatus is revised and redescribed, and its distribution is here restricted to Rio de Janeiro state. Externally, the new species differs from M. gummatus in having distinct protoconch color and sculpture, teleoconch sculpture marked by strong anastomosing rugosities and malleations, and lighter colored white-greyish head-foot. Internally, it presents distinct jaw and radular features, a talon, and a long convoluted penis bearing two flagella. Additional comparisons with other Brazilian congeneric species are also provided.


INTRODUCTION
Strophocheilid gastropods belonging to the subfamily Megalobuliminae Leme, 1973 and the genus Megalobulimus Müller, 1878 are the largest native South American Eupulmonata, with a shell length usually ranging from 50 -160 mm. There are currently 55 species recorded from Brazil (Simone, 2006;Birckolz et al., 2016), most of which are found in the Atlantic Forest. These snails are threatened with environmental destruction and contamination, a problem aggravated by their high regional endemism and the introduction of exotic species (Mansur & Leme, 1996;Simone, 1999;Lydeard et al., 2004).
The two most extensive revisions of Strophocheilidae performed in the 20 th Century by Bequaert (1948) and Morretes (1952) were mostly based on shell characters and presented very distinct results and conclusions. Divergences between these revisions can be partly explained by intraspecific variation of terrestrial gastropod shells (Mayr, 1977). Leme (1971Leme ( , 1973 argued that shell characters alone might be insufficient for comparative studies on Megalobulimus due to intraspecific variation and overlapping characters, but shell-based descriptions are still very frequent and substantial (e.g., Fontenelle et al., 2014;Simone, 2018). Even so, several works have consistently shown that more accurate conclusions can be drawn from associating shell characters with anatomical features, especially those focused on the digestive, reproductive, and excretory organs (Leme, 1989;Leme & Indrusiak, 1995;Borda & Ramirez, 2016). Ideally, such analyses should also include paleontological, ontogenetic, molecular, and ecological data, using a holomorphological approach (Leme, 1971;Wheeler, 2008).
In a wide-range comparative study on the number of recognizable species under different species concepts by Agapow et al. (2004), gastropods emerged as the only group that had a reduced number of species under the phylogenetic species concept compared to the biologi-cal concept. This indicates an excess of synonyms and a subsequent need for comprehensive revisions, which is especially true for Megalobulimus.
In a review of Megalobulimus specimens from the collection of the Museu de Zoologia da Universidade de São Paulo (MZSP), we found a seemingly consistent assemblage of individuals from São Paulo and Paraná states labeled as M. gummatus (Hidalgo, 1870). These individuals proved to be conchologically and anatomically divergent from populations of M. gummatus from the type locality in northern Rio de Janeiro state, which have shells similar to the holotype of M. gummatus ( Fig. 10A-C). The southern individuals are introduced herein as a new species, and we provide a redescription of M. gummatus based on type material and specimens from Rio de Janeiro for comparative purposes.

MATERIAL AND METHODS
Specimens studied herein are deposited in the Mollusca Collection of the Museu de Zoologia da Universidade de São Paulo (MZSP). Shell measurements  and the number of shell whorls follow Bequaert (1948). Dissections were carried out following the methods of Leme (1973) and Simone & Leme (1998). Radulae were spur-coated with gold and examined under SEM in the Laboratório de Microscopia Eletrônica, MZSP.
Head-foot: Tegument in living specimen very light-colored, from dirty white to grayish-bluish ( Fig. 1); each buccal flange bearing seven papillae.
Inner surface of proximal intestine with large intestinal typhlosole (Figs. 6C-D: it) and parallel folds (p1-p5); distance between folds p1 and p2 slightly wider; fold p4 (Figs. 6C-D: p4) reaching pre-rectal valve (Fig. 6D: va), continuing as post-valve central longitudinal fold, low and wide (Fig. 6D: p6), surrounded by oblique, post-valvar compact folds (Figs. 6D-E: p7). At final third of rectum ( Fig. 6E), fold p6 extinguishing, p7 folds becoming anastomosed into four bulging rectal folds (Fig. 6E: rf ), progressing in part beyond aperture of anus ( Fig. 6E: an) into inner edge of pneumostome. Distribution and habitat: Megalobulimus dryades sp. nov. was initially recorded in the Vale do Ribeira region, in São Paulo state. It is found mainly in the middle and lower Rio Ribeira do Iguape Basin in southern São Paulo and northeastern Paraná states (Fig. 9). Apparently, this species has a high environmental tolerance, and its range may have been expanded by humans who used its shells in handicrafts. Agudo-Padrón (2010, 2011) recorded its presence in Santa Catarina state, identified as M. gummatus (non Hidalgo).
Ecology: Sobreira & Molina (2002) studied the reproduction of M. dryades sp. nov. (referred to as M. gummatus in their study) based on three specimens from Vale do Ribeira. Egg-laying occurred in two periods, a longer one between April and May and a shorter one between September and November. Specimens laid 2 to 5 eggs per clutch, with average hatching of 52.4% after a development period of 60 days (n = 21). The mean egg size was 28.6 × 21.3 mm (n = 26).

Etymology: The comprehensive classification of the Brazilian phytogeographic regions proposed by Carl
Friedrich Philipp von Martius (1840-1869) divided the country into phytogeographic provinces named after nymphs from Greek mythology. The name Dryades was used to designate the region roughly corresponding to the current Brazilian Atlantic Forest. This biome has been reduced to about 15% of its original territorial coverage. The Vale do Ribeira region is the largest continuous reserve of this threatened biome, thus our inspiration for the specific epithet, which is used herein as a noun in apposition.  Ribeira region in the late 19 th -early 20 th centuries, and were deposited in the Museu Paulista (currently MZSP). When Morretes (1949Morretes ( , 1953 published his catalog of mollusks from Brazil, he considered those samples as representatives of southern populations of M. gummatus inhabiting the states of São Paulo and Paraná. This concept was maintained in subsequent compilations (Salgado & Coelho, 2003;Simone, 2006). Meanwhile, the concomitant erroneous use of another name, Megalobulimus chionostoma (Mörch, 1852), to refer to true M. gummatus specimens caused further taxonomic confusion. Apart from the white peristome and a glossy periostracum, the shells of M. dryades sp. nov. and M. gummatus present some coincidental features such as large size, a dorsoventrally compressed outline, similar protoconch macrosculpture, and pigmented shell matrix with a white subsutural band (Figs. 2D, 10). However, M. dryades sp. nov. differs in having a darker protoconch with a clearly marked lighter subsutural band, with a sculpture lacking any distinct spiral elements, consisting of more pronounced axial riblets that branch apically near the suture, and microscopic granules. It also has a lower spire, a body whorl with a strongly corrugated surface with malleations, a less reflected but thicker peristome with a more rounded outer lip, and a thicker, oblique, and slightly convex columella.

Measurements
The soft parts of M. dryades sp. nov. are lighter-colored externally compared to M. gummatus. Internally, differences in the digestive system reside in the more robust mandible with narrow, well-marked columns, and the configuration of the radular teeth. The genital systems are also distinct, as M. dryades sp. nov. has a long and uniform penis and an epiphallus bearing two flagella. The presence of a talon and a free oviduct appendix further distinguishes it from M. gummatus, which in turn seems more closely related to species of the so-called "M. ovatus species complex" sensu Leme (1989Leme ( , 1993 due to the lack of these two last characters. Finally, both species present isolated distributions and distinct habitats (see M. gummatus, below).
Head-foot: Tegument yellowish to light gray.
Digestive system: Buccal mass less robust; jaw equally rigid, elasmognate and pigmented (Fig. 11A) with ~17 irregular, round and wide axial columns, and fine transverse growth lines.
Radula (Fig. 11B): With ~95 rows of compressed teeth (47-1-47); lateral teeth rectangular, 1.5 times as long as wide, with single, short, obtuse medially displaced cusp; basal plate limited to corniform lateral extension. Central tooth 20% smaller, elliptical shape, with apical extensions of basal plate fit anterior tooth. Distribution and habitat: Hidalgo (1870) reported the location of the type specimen as "Province of Rio de Janeiro, occurring among plants where the vegetation is more abundant, being uncommon". The locations of the shells studied by Bequaert (1948) included Cabo Frio (Rio de Janeiro state, RJ), the Corcovado, in the city of Rio de Janeiro, the Mantiqueira Mountain Range near Rio de Janeiro, and 'Gregugi' [sic] River (possibly a misrepresentation of Gongogi River) in Bahia state. Its presence was recorded in archaeological sites in the Camboinhas shellmound, in Niteroi, Rio de Janeiro state, probably transported by humans (Mello & Coelho, 1989). Judging by the distribution data of M. gummatus specimens from the MZSP collection, its range seems to be currently restricted to the area between Cabo Frio and Arraial do Cabo on the northern coast of Rio de Janeiro state (Fig. 9), in the so-called Região dos Lagos. This region is a semiarid, 1,500 km² ecological enclave in the humid Atlantic Forest known locally as Caatinga Fluminense. The area is under influence of the oceanic resurgence of the Falkland cold water stream and seasonal winds that dispel clouds and reduce temperature and annual precipitation to about 800 mm. The regional vegetation is considered as a relic of a dry and cold Pleistocene and includes xerophilic Restinga and seasonal forests (Coe & Carvalho, 2013).

DISCUSSION
The new species described here was previously understood as a southern population of M. gummatus, a species that appears to be restricted to Rio de Janeiro state. Shells of M. dryades sp. nov. were often used in handicrafts, and its capture and transportation for this purpose may be the cause of the apparent range expansion or introduction to relatively distant locations (Fig. 9). The new species is, however, readily distinguishable from the northern species by its peculiar conchological and anatomical characters.
Although the completely white peristome distinguishes M. dryades sp. nov. from most Brazilian congeneric species, a more extensive comparison is required to distinguish it from M. chionostoma (Mörch, 1852), M. terrestris (Spix, 1827, M. oosomus (Pilsbry, 1895) andM. valenciennesii (Pfeiffer, 1842), all of which also have a white peristome and occur in eastern Brazil (Simone, 2006). In that regard, M. dryades sp. nov. can be told apart from M. chionostoma (Fig. 13A-F) by the narrower body whorl and shorter but wider aperture, different ground color, and glossy periostracum. Moreover, the shell of M. chionostoma falls within a typical M. ovatus pattern (Bequaert, 1948) consisting of a large, elongated shell (Fig. 13A, D), body whorl surface with chisel-like marks (much more delicate than M. dryades sp. nov.), and nepionic shell bearing distal, wide, and incomplete ribs (Fig. 13F). Morretes (1953) reported two records of M. chionostoma in Macaé, RJ (Morretes, 1953: figs. 46-48), and Bequaert  Fonetenele, J.H. et al.: New Megalobulimus from the Atlantic Forest Pap. Avulsos Zool., 2021;v.61: e20216144 12/17 (1948) considered these records reliable. Some of the MZSP specimens examined herein come from Ubatuba, on the northern coast of São Paulo. The taxon M. chionostoma has occasionally been misused to designate M. gummatus, due to the superficiality of Mörch's (1852) original description. According to data from specimens deposited in the MZSP, the range of both species overlap along the coast of Rio de Janeiro.
Remarkably, M. dryades sp. nov. resembles M. terrestris (Fig. 14A-B), which has a protoconch with spaced complete ribs, a thick but only slightly expanded white peristome, a dorsoventral compression, and a subsutural band (Bequaert, 1948). However, it differs from M. terres-tris by having a much longer shell, and its columella is larger and not arched. In M. terrestris, the shell is medium-sized (L = 77-110 mm) and has a peculiar sculpture on the last whorl (Pilsbry, 1895), which consists of fine microscopic streaks (Rang, 1831) resulting in a hazy periostracum surface. Moreover, M. terrestris occurs in the semi-arid Caatinga biome in northeastern Brazil, a very different environment with annual precipitation of about 800 mm, between the states of Bahia, Sergipe, Alagoas, Pernambuco, Paraiba, and Rio Grande do Norte.
Megalobulimus dryades sp. nov. may also resemble M. oosomus (Fig. 14C-F) mainly because of the considerably thickened, expanded peristome, and similar pro- toconch morphology. Nevertheless, M. dryades sp. nov. differs by the larger size, proportionally larger spire, and by the peculiar body whorl surface with fewer delicate marks and lacking minute sparse and irregular granulations (Pilsbry, 1895). M. oosomus was described based on a single shell from Brazil. Bequaert (1948) tentatively used the name for more inflated variations of M. terrestris with a very convex body whorl and short, broad spire, blunter apex, and less dorsoventrally compressed shells. Among the specimens diagnosed as M. oosomus by Bequaert, some from the municipalities of Morretes and Antonina in Paraná state (thus being sympatric with M. dryades sp. nov.) have a pinkish peristome. We assume that the M. oosomus specimens with a pinkish peristome referred to by Bequaert on the coast of Paraná are variations of M. paranaguensis Pilsbry & Ihering, 1900. Morretes (1949, 1953, Salgado & Coelho (2003), and Simone (2006) still reported the occurrence quoted by Pilsbry (1895) but did not add new locations for M. oosomus. Ramírez et al. (2012) recorded its presence in the Brazilian Amazon.
Shells of M. dryades sp. nov. are similar to M. valenciennesii (Fig. 14G-H) due to their large size (the latter frequently attains L~125 mm), spire with pigmented matrix, the presence of a lighter subsutural band, and white peristome. They differ from M. valenciennesii in not having the body whorl densely covered by microscopic, vertical striolae of the periostracum. Its shell also lacks the typical zigzag discolored areas (Fig. 14H) and the flaked peri-  ostracum seen in M. valenciennesii (Bequaert, 1948 The division of the previous concept of Megalobulimus gummatus into two species, with the "true" M. gummatus occurring in the northern Rio de Janeiro area and M. dryades sp. nov. southward in the São Paulo-Paraná region, has clear implications for conservation efforts. Land snails are widely regarded as some of the most threatened animals on the planet. They are under constant pressure due to anthropic activity and present very high extinction rates (Lydeard et al., 2004;Régnier et al., 2009). Brazilian land snails are not an exception (Salvador, 2019), and the scenario for Megalobulimus species may be even harsher. Despite their large size, they are relatively fragile creatures compared to a local competitor, the very aggressive African invader Lissachatina fulica (Férussac, 1821), which has been reported from the Vale do Ribeira region since 2006 (Eston et al., 2006). While we recognize a species that was once widely distributed as two entities with more limited ranges, we also understand that, in this case, more restricted geographical distributions might mean greater vulnerability. Thus, urgent protective measures must be enforced. The Megalobulimus snails have been considered as umbrella and flagship species for the conservation of the Atlantic Forest biome (Santos, 2011). Though this initiative would certainly increase public awareness of these animals and their environment, we believe that more efforts are still necessary to avoid permanent biodiversity loss. Our results reinforce the urgency to better understand the taxonomy and basic biology of Brazilian Megalobulimus and land snails in general, which is a fundamental step towards effective conservation policies.