Cerithiidae, Litiopidae, Modulidae and Planaxidae (Gastropoda, Cerithioidea) collected by the Marion Dufresne MD55 expedition in southeastern Brazil

. Several deep-water mollusks collected during the Marion Dufresne MD55 expedition off SE Brazil have been studied in recent papers. The present work focuses on eight species belonging to the cerithioidean families Cerithiidae, Litiopidae, Modulidae and Planaxidae. Three species have their geographic distributions greatly expanded: Bayericerithium bayeri Petuch, 2001 from Pernambuco to Rio Grande do Norte and Ceará states (north) and to Bahia and Espírito Santo states (south), Brazilian coast; Ittibittium oryza (Mörch, 1876), from the Caribbean to the SW Atlantic; and Angiola lineata (Costa, 1778), from Trindade Island, Brazil to the Abrolhos Slope, nearly 870 km westward. Four species reported herein had their bathymetric ranges greatly expanded: Alaba incerta (d’Orbigny, 1841) from 0-40 m to 300 m; B. bayeri from 0-2 m to 120 m (live specimens); Litiopa melanostoma Rang, 1829 from 0-805 m to 1,550 m; Fossarus orbignyi Fischer, 1864 from 0-40 to 830 m (shells only).


INTRODUCTION
The MD55 cruise of R/V Marion Dufresne took place in May and June 1987 as a joint project of the Muséum national d'histoire naturelle (MNHN; Paris, France) and Universidade Santa Úrsula (USU; Rio de Janeiro, Brazil) (Tavares, 1999). The expedition recovered numerous deep-water mollusks from the southeastern Brazilian coast. Most of this material remained unstudied for years, but recent efforts have been steadily changing this scenario, e.g., comprehensive reports on Triphorinae (Fernandes et al., 2013), Naticidae (Simone, 2014), Fissurellidae (Simone & Cunha, 2014), Seguenziidae , and Calliostomatidae (Cavallari et al., 2019). The present work focuses on a small assembly of species belonging to the cerithioidean families Cerithiidae, Litiopidae, Modulidae and Planaxidae.
Litiopids are considerably less diverse if compared to cerithiids and planaxids, with a total number of species estimated at 16-18 (Strong et al., 2011). Nevertheless, they are a widely distributed group of small-sized sea snails (less than 25 mm in length) that occur among algal and seagrass fronds in shallow, warm-temperate and tropical seas (Houbrick, 1987a Wells, 1998;Strong et al., 2011). Two species have been recorded in the Western Atlantic to date, Alaba incerta (d'Orbigny, 1841) and Litiopa melanostoma Rang, 1829 (Rios, 2009;Rosenberg, 2009).
The Planaxidae are a family of largely marine, tropical to subtropical snails, usually inhabiting rocky shores. Remarkably, they brood eggs in a special head-foot concavity (Simone, 2001). With a total number of valid species estimated at 30-40 (Strong et al., 2011), planaxids are represented in Brazil by two species: Angiola lineata (Costa, 1778) and Fossarus orbignyi Fischer, 1864 (Rios, 2009).
Herein we provide updated taxonomic information on eight species belonging to the above-mentioned families. We report new records from the MD55 expedition, some of which are complementary to previous works (e.g., Leal, 1991) and represent relevant geographic and bathymetric range extensions.

MATERIAL AND METHODS
The MD55 specimens studied herein consist of shells from the collections of the Muséum national d'histoire naturelle (MNHN) and Museu de Zoologia da Universidade de São Paulo (MZSP), Brazil. Additional material from the Academy of Natural Sciences of Drexel University (ANSP), Philadelphia, USA, was also analyzed. The malacologists onboard of the R/V Marion DuFresne, namely Philippe Bouchet, José H. Leal and Bernard Métivier, recovered the above-mentioned MD55 specimens among the extensive material collected by the expedition. Sampling methods employed included Blake and Beam trawls, a Charcot dredge, and a Box corer at 67 stations along the continental platform of Rio de Janeiro and the Vitória-Trindade Seamount Chain (for detailed information, see Tavares, 1999). Examined material lists are given in each species entry. Photographs and measurements were obtained using a Zeiss AxioCam MRc 5 and Zeiss AxioVision SE64 Rel 4.8 imaging software. Unless otherwise stated, only MD55 specimens were measured. The following abbreviations are used throughout the text for shell measurements: H, shell height; W, shell width; h, aperture height; w, aperture width.

Remarks:
Although all the MD55 specimens are juvenile empty shells (Figs. 11-12), they compare exceedingly well with the earliest whorls of well-preserved adult specimens from relatively close locations. Adult B. bayeri have thick, stubby shells, but the initial spire whorls have a straight conical outline in some specimens (Petuch, 2001: fig. 1A-C). Ground color is cream-white, with widely spaced orange bands arranged in a zebra-like pattern, as reported by Petuch (2001) in the original description.
In the present specimens, these colors are sometimes mixed with a diffuse violet-pinkish shade, especially in the initial 2-3 teleoconch whorls. The MD55 specimens also have poorly developed sculpture except for very faint subsutural knobs and numerous densely packed spiral threads, which compares well with the original description. The distribution of B. bayeri was originally restricted to Pernambuco, but it is herein greatly expanded ca. 510 km northward to Rio Grande do Norte and Ceará states, and ca. 1,350 km southward to the states of Bahia and Espírito Santo. Petuch (2013) considered B. bayeri endemic to the Cearaian Biogeographic Subprovince (sensu Petuch, 2013), but the records reported herein are evidence of a wider range. In this sense, the species also occurs in the author's neighbor Bahian Province (from Alagoas to Rio de Janeiro states). The species' bathymetric range is also expanded as live specimens were collected at depths of up to 120 m (the only deeper record consists of empty shells, which were probably carried). Bayericerithium has been recently listed as a synonym of Cerithium in online taxonomic databases (e.g., Rosenberg, 2009Rosenberg, , 2014, which also list Cerithium bayeri (Petuch, 2001) as the valid combination. However, there is a Cerithium bayeri Beets, 1941, a fossil species from the Miocene of Indonesia (Beets, 1981). This would make C. bayeri (Petuch, 2001)

Remarks:
Though none of the specimens studied herein were collected alive (Fig. 19), the present records of well-preserved specimens represent a bathymetric expansion from the previously reported range of 0-805 m (Rosenberg, 2009), going as deep as 1,540-1,550 m. Nevertheless, this is a pelagic species that lives attached to floating debris (Higo et al., 1999). The present material was probably carried by debris floating at the surface level to the localities reported herein, and the shells sunk after death. Cavallari, D.C. et al.: MD55 Cerithioideans Pap. Avulsos Zool., 2020;v.60: e20206035 4/10 (29) apical views. Cavallari, D.C. et al.: MD55 Cerithioideans Pap. Avulsos Zool., 2020;v.60: e20206035 7/10 herein are known to live attached to floating debris and algae (e.g., Alaba incerta, Litiopa melanostoma; Higo et al., 1999) and were most likely carried to the collection localities along with their respective floating substrates, sinking after death. The deepest records for these species reported in the literature, including the ones presented herein, consist of empty shells. On the other hand, some of the remaining species found in the present samples can live in deeper waters, especially Bayericerithium bayeri (1-120 m) and Modulus modulus (1-105 m) . Unfortunately, the specimens had no soft parts, which prevents further analysis. One of the species studied herein, Ittibittium oryza, is reported from the southwestern Atlantic for the first time. This is not unprecedent, since several papers based totally or partially on MD55 material reported the presence of genera and species of gastropods previously unrecorded in the Southwestern Atlantic (e.g., Fernandes et al., 2013;Simone & Cunha, 2014;Salvador et al., 2014;Cavallari et al., 2019;Fernandes & Pimenta, 2020). Significant range expansions of over 1,000 km have also been frequently reported in these studies (e.g., Cavallari et al., 2014;Salvador et al., 2014;Simone & Cunha, 2014;Cavallari et al., 2019). In many cases, the new records leave large occurrence gaps (e.g., some species recorded in the Caribbean and off southeastern Brazil, as in I. oryza). Actually, this may not reflect a real absence of occurrence, but rather an absence of samplings and studies (Fernandes & Pimenta, 2020), which reinforces the importance of the present and other similar efforts.
Bringing information about the Brazilian deep-water fauna into light has become an urgent task in face of the potential biodiversity loss due to oil extraction activities that are currently being or will be carried out in the country (Meira et al., 2016;Francini-Filho et al., 2018). Some of the extraction areas are or may be within the region sampled in MD55 expedition (Romero et al., 2011), which makes the matter even more critical. The MD55 material is a partial portrait of the deep-sea fauna of southeastern Brazil from over 30 years ago. The changes that this fauna could have undergone since then, and what could be the impacts caused by the oil extraction activities are important questions, which should be addressed in future studies.