A new species of Microcancilla from the southwestern Atlantic and notes on Microcancilla brasiliensis comb. nov. (Gastropoda, Cancellariidae)

Microcancilla phoenix sp. nov., collected from the Southeast and South coast of Brazil represents the southernmost record of the genus in the Atlantic Ocean. The new species differs from the other congeners of the Atlantic mainly by the presence of microscopic pustules covering the whole shell and by dimensions of the protoconch. “Axelella brasiliensis” Verhecken, 1991, known from the Northeast to South coast of Brazil, is transferred to Microcancilla based on a similar sculpture of microscopic pustules on the protoconch and on other features of the teleoconch discussed in the present study.


INTRODUCTION
Cancellariidae Forbes & Hanley, 1851 comprises marine gastropods that inhabit several types of soft bottoms, characterized by small to medium sized, fusiform to ovate shells with gradate to scalariform shapes. They are dextrally coiled and commonly bear axial and spiral sculptures that produce a cancellate or reticulate surface (Harasewych & Petit, 1998;Petit & Harasewych, 2005). Cancellariids are found from Arctic to Antarctic seas and in a great bathymetric range, including shallow waters to the deep sea (Harasewych & Petit, 2014).
Cancellariidae is currently classified in the superfamily Volutoidea Rafinesque, 1815 together with Volutidae Rafinesque, 1815 (Bouchet et al., 2017). The family includes about 350 valid extant species (MolluscaBase, 2019) distributed into 67 genera (extant and fossils), and to date three subfamilies are recognized: Admetinae Troschel, 1865, Cancellariinae Forbes & Hanley, 1851and Plesiotritoninae Beu & Maxwell, 1987(Bouchet et al., 2017. Admetinae usually comprise species with smaller, thinner shells, which lack an umbilicus and columellar folds; Cancellariinae usually comprise species with heavy shells, strongly to weakly shouldered, with stronger reticulate or cancellate sculpture, weak varices, two to three columellar folds, and presence or absence of an umbilicus; Plesiotritoninae usually comprise species with a high spire presenting varices and non-collabral axial sculpture (Harasewych & Petit, 1998). However, some genera have a doubtful position and are not assigned to any of these subfamilies by MolluscaBase (2019).
Microcancilla Dall, 1924 is currently considered a member of Admetinae (MolluscaBase, 2018). This genus was erected without a diagnosis and only including Microcancilla microscopica (Dall, 1889). More recently, Barros & Petit (2007) described Microcancilla jonasi despite uncertainties about the generic classification. To date Microcancilla only encompasses Atlantic species, but Barros & Petit (2007) stated that there are some species from the central Pacific clearly attributable to this genus. Microcancilla microscopica is known from the Northwest Atlantic (Dall, 1889) and M. jonasi is known only from the continental slope off Pernambuco, Northeast Brazil (Barros & Petit, 2007).
In this paper, we describe a new species of Microcancilla from the Southeast and South coast of Brazil. Reassessment of material of "Axelella brasiliensis" Verhecken, 1991 also suggests the classification of this species in Microcancilla.

MATERIAL AND METHODS
Specimens examined herein were collected mainly by two projects: 1) "Programa de Avaliação do Potencial Sustentável de Recursos Vivos da Zona Econômica Exclusiva" [Program of Evaluation of the Sustainable Potential of Living Resources in the Economic Exclusive Zone] (REVIZEE Sul), which sampled the Southeast and South coast of Brazil, between December 1997 andApril 1998, aboard Research Vessel (RV) Prof. W. Besnard; 2) "Importância e caracterização da quebra da plataforma para recursos vivos e não vivos -Programa de Apoio ao Desenvolvimento Tecnológico e Científico" [Importance and characterization of the continental shelf break for living and non-living resources -Support Program for Technological and Scientific Development] (PADCT), between November 1997 and January 1998, aboard RV Prof. W. Besnard. Table 1 presents data on the collecting stations where the present material was found. Specimens examined consist only of empty shells. The number of examined specimens is indicated in brackets in the material examined section. Most of the material studied here was housed in the "Museu Nacional, Universidade Federal do Rio de Janeiro". Due to the fire of September 2018 (Zamudio et al., 2018), most of the vouchers were destroyed and in these cases the catalog numbers are followed by a dagger ( †).
Shells were studied using a Scanning Electron Microscope (SEM) JEOL JSM-6390LV at the "Centro de Microscopia Eletrônica, Departamento de Invertebrados, Museu Nacional, Universidade Federal do Rio de Janeiro". Photographs of shells were taken using an AxioCam ICc5 camera coupled to a Zeiss Discovery.V20 stereomicroscope and automated stacking.
Abbreviations for measurements: AL = aperture length; AW = aperture width; BWL = body whorl length; SL = shell length; SW = shell width. Protoconch whorl countings follows Verhecken (2007).    Etymology: phoenix (Latin) refers to a fabled bird symbolic of resurrection and immortality; the epithet is named in honor of the "Museu Nacional". Epithet as a noun in apposition.
Bathymetric range: From 50 m to 490 m.

Remarks:
The previously selected type series of M. phoenix sp. nov., including the holotype, was destroyed by the fire of "Museu Nacional". An additional shell was obtained later; in spite of it being a younger and partially broken shell, we choose a preserved specimen as the name-bearing type of M. phoenix (Fig. 1A). Microcancilla microscopica (Dall, 1889), known from Florida, USA, and western Caribbean, has a smaller protoconch (Lectotype USNM 82977, designated by Barros & Petit (2007: 99), 0.75 whorls, 560 µm wide vs. Holotype of M. phoenix, 1.25 whorls, 700 µm wide), wider parietal region, and a shorter siphonal canal (Barros & Petit, 2007: figs. 9-11).
Microcancilla jonasi Barros & Petit, 2007, known from Northeast Brazil, differs by the very faint spiral sculpture with stronger axial ribs and by the flatter and narrower subsutural region resembling a crown as a result of the axial sculpture (Barros & Petit, 2007: figs. 1-8).

Bathymetric range: From 206 m to 637 m.
Remarks: Petit (2012) included this species in Pseudobabylonella Brunetti, Bella, Forli & Vecchi, 2009, possibly by the statement of Brunetti et al. (2009: 66): "The new genus [Pseubabylonella], which is characterized mainly by the sculpture of the protoconch, comprise species previously included in Axelella and Babylonella" [translated from Italian]. Brunetti et al. (2009) described a protoconch with numerous well-developed spiral and axial cords of sinuous outline.
The holotype of Microcancilla brasiliensis comb. nov. has an eroded protoconch (Verhecken, 1991: fig. 6) which precludes the analysis of microsculpture. Verhecken (2002) reported new records of M. brasiliensis (as "Axelella brasiliensis") and figured a more preserved protoconch, but the illustrations do not allow for an assessment of the microsculpture and no sculpture was described.
The additional material M. brasiliensis studied here shows microscopic pustules arranged fairly in spiral lines and at irregular intervals (Figs. 3E, G) on the protoconch, which differ from the sculpture pattern of Pseudobabylonella. The protoconch-teleoconch transition in M. brasiliensis is not clearly marked like in Pseudobabylonella, in which the reticulated teleoconch sculpture starts as faint axial ribs (Fig. 3E). Thus, the protoconch morphology of M. brasiliensis is more similar to M. phoenix, and we decide to include this species in Microcancilla rather than in Pseudobabylonella despite uncertainties.
Microcancilla phoenix (Figs. 1A-H, 2A-F) has microscopic pustules covering the whole shell, not restricted to the protoconch like M. brasiliensis. Additionally, M. phoenix has a more rounded aperture and subsutural region (Figs. 1A, B), while M. brasiliensis has a more triangular aperture and a flatter shoulder (Fig. 3A).

DISCUSSION
The species treated in this study are tentatively placed in Microcancilla by the similarity of the general shell shape, size, and absence of distinct columellar folds like in M. microscopica. Despite this, M. phoenix sp. nov., and M. brasiliensis comb. nov. have a microsculpture of pustules on the protoconch and/or teleoconch (Figs. 1E-H, 2C, 3E, G), a feature not described in M. microscopica and in M. jonasi under SEM examination by Barros & Petit (2007). Souza, L.S. et al.: A new species of Microcancilla from Brazil Pap. Avulsos Zool., 2021;v.61: e20216129 5/8 Another possible generic placement for the species treated herein is Zeadmete Finlay, 1926, discussed by Petit & Harasewych (2000), Bouchet & Petit (2008) and Verhecken (2011). Zeadmete also has weak, almost obsolete folds in the inner lip (Bouchet & Petit, 2008: 2), but there is no mention about microscopic pustules covering the protoconch and/or teleoconch. Zeadmete atlantica Petit, Campbell & Campbell, 2010 is the only species of the genus reported for the Atlantic Ocean.
Cancellicula Tabanelli, 2008 was erected to comprise fossil species of the Pliocene (Tabanelli, 2008) and shares some conchological features with Microcancilla, such as the general shape of the shell and the absence of columellar folds (Brunetti et al., 2009). The fossil species assigned to this genus, Cancellicula dregeri (Hoernes & Auinger, 1890) (type species) and Cancellicula profunda (Tabanelli, 1985), differ from Microcancilla by having a multispiral protoconch, sculptured by a weak spiral cord and thin orthocline axial ribs, and by the flatter shoulder of the teleoconch whorls (Brunetti et al., 2009). More recently, Verhecken (2011) included Admete aethiopica Thiele, 1925, an extant species from the Indian and Pacific Oceans, in Cancellicula. The protoconch of Cancellicula aethiopica (Thiele, 1925) is more similar to the protoconch of Microcancilla, which is paucispiral and presents a microsculpture of small pustules arranged spirally (Verhecken, 2011: pl. 15, fig. 3A-B). Despite proposing the classification of the latter species in Cancellicula, Verhecken (2011: 40) stated that "the relation between Microcancilla and Cancellicula may need further study".
The genus Microsveltia Iredale, 1925 also includes species with size and shape similar to Microcancilla, but the type species (Microsveltia recessa Iredale, 1925) and most species included in the genus have two columellar folds and lack any microsculpture, except for Microsveltia tupasi Verhecken, 2011(Verhecken, 2011. The shell of M. tupasi is completely covered by a microsculpture of arrowheads and T-characters pointing adaperturally, arranged in spiral and axial rows (Verhecken, 2011: pl. 11, fig. 3, pl. 15, figs. 2A-B). Moreover, due to the species having no columellar fold and Verhecken (2011) was unsure about the generic and even familial placement of M. tupasi.
The generic classification of small cancellariids (less than 10 mm), especially for deep-sea species (Maxwell, 1992;Barros & Petit, 2007) is still obscure. Provisional generic classifications often occur in these groups and a more comprehensive study about these and other similar genera of Cancellariidae is still necessary to substantiate an accurate classification of these species.
The present study expands the geographic distribution of Microcancilla southwards to the Southwest Atlantic (~32°S) (Fig. 4). Microcancilla brasiliensis and M. phoenix show a wider latitudinal range (Fig. 4) in comparison to their congeners. The distribution of this genus remains restricted to the Atlantic Ocean (Fig. 4).

ACKNOWLEDGMENTS
We are grateful to "Ministério do Meio Ambiente" and "Conselho Nacional de Desenvolvimento Científico e Tecnológico" (CNPq) for the financial support of the projects REVIZEE Sul and PADCT; to C. Messias (MNRJ) for SEM micrographs. We are deeply grateful to A. Verhecken (RBINS) for discussions on an early version of this manuscript and for sharing literature. Also, we wish to thanks the anonymous referees and the editors C. Lamas and L. Simone for the revision of the manuscript. The senior author also thanks CNPq and "Conselho de Aperfeiçoamento de Ensino Superior" (CAPES) for a doctoral scholarship (CNPq/MCTI/FAP/PROTAX #001/2015).

AUTHORS' CONTRIBUTIONS
L.S.S. and C.M. sorted the samples. A.D.P. provided the resources. All authors actively participated in the conceptualization, investigation, description of specimens, results and discussion. L.S.S. produced the original draft and all authors reviewed and approved the final version of the paper.