Addisonia enodis (Vetigastropoda: Lepetelloidea) associated with an elasmobranch egg capsule from the South Atlantic Ocean and the discovery of the species from deep waters off northeastern Brazil

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Introduction
Lepetelloidea is one of the least investigated groups of marine gastropods, whose species richness is sporadically approached by alpha-taxonomic studies, especially from the South Atlantic Ocean (Simone 1996, Leal & Simone 2000, Simone & Cunha 2003, Lima 2014, Lima et al. 2016).
Addisonia enodis Simone, 1996 was described based on three specimens, one of which had soft parts that were dissected and supported the anatomical definition of the species.The main characters that differentiate A. enodis from congener species were the lack of radial sculpture, the position of the gill and shell muscle, as well as the shape of the rachidian teeth (Simone 1996: 784).Roldán & Luque (2010: 209) did not recognize conchological, radular and geographical differences in A. enodis Simone, 1996 for its separation as a different species, considering it a synonym of A. excentrica.
The present paper recognizes Addisonia enodis as a valid species and extends its distribution to northeastern Brazil based on specimens found in deep waters off the state of Sergipe.Furthermore, this genus is reported here for the first time associated with an elasmobranch egg capsule from the South Atlantic Ocean.

Material and methods
The present paper is based on the study of specimens collected by the R/V 'Natureza' using a trawling dredge between 365 to 500 meters depth on the continental slope of the states off Sergipe (northeastern Brazil) as part of benthic studies of the "Programa de Avaliação do Potencial Sustentável de Recursos Vivos na Zona Econômica Exclusiva (REVIZEE/2000-2001)", and specimens collected using a trawling dredge and trawl between 50 to 60 meters depth on the continental shelf of the states off Rio de Janeiro and São Paulo (southeastern Brazil) in 2001 to 2002.Other specimens collected in 1987 by the R/V 'Prof.W. Besnard' from the continental shelf off southeastern Brazil were reexamined (Simone 1996).
Elasmobranch egg capsules were obtained using a trawl net during the pink shrimp fishery on the continental shelf of the state off São Paulo.Capsules were placed in a container with ice and then taken to the Laboratory of Malacology (MZSP -Museu de Zoologia, Universidade de São Paulo, São Paulo, Brazil) for opening and removal of embryos.A living specimen of Addisonia enodis was found inside a capsule and then fixed in 70% ethanol.

Ecology
This species may be found on sand to mud bottoms between 50 to 365 m depth from Brazilian waters, associated with egg capsules of Atlantoraja castelnaui.

Geographic distribution
Northeastern (Sergipe state -present study) to Southeastern Brazil (Rio de Janeiro and São Paulo states -Simone 1996).

Discussion
We believe that conchological, anatomical and radular variations among specimens of A. excentrica and A. enodis need to be further investigated, especially based on a large sample of Addisonia from Brazilian waters, to ascertain if both species are actually conspecific.In this case, it is important to keep its status as a valid species rather than synonymize them, until further data, including molecular analyses, clarify this issue.
The present paper reports the association of Addisonia with an elasmobranch egg capsule of the family Arhynchobatidae Nelson, 2006 for the first time.Addisonia enodis was found living inside the egg capsule of Atlantoraja castelnaui from Brazilian shallow waters (between 50 to 60 m depth).This skate occurs from the Southeastern Brazil to Argentina waters, usually living between 10 to 100 m depth, and lay pairs of eggs on sandy or muddy bottoms (Bornatowski & Abilhoa 2012).Further information is not yet available for A. enodis, despite the fact that some of the abovementioned sharks and rays occur along the Brazilian coast.
The samples studied here from the continental slope off northeastern Brazil reinforce the possibility of live specimens of Addisonia being less abundant in deeper waters.It is likely that the specimens usually live in shallower waters (up to 100 m) due to greater abundance of elasmobranch egg capsules (especially of skates of the family Arhynchobatidae Nelson, 2006) which are biologically associated.Particularly, Scyliorhinidae, Rajidae, and now Arhynchobatidae, are potential families to find specimens of Addisonia and possibly other gastropods [e.g., Choristella Bush, 1897 (McLean 1992)] associated with their eggs in Brazilian waters based on common records in other eco-regions (McLean 1985, Ragozzi 1985, Villa 1985, Mclean 1992, Dantart & Luque 1994, Roldán & Luque 1999, 2010) and the greater richness of known elasmobranchs (especially Rajidae) on the Atlantic Coast of South America.