South America-Africa missing links revealed by the taxonomy of deep-sea molluscs: Examples from prochaetodermatid aplacophorans

Synopsis of the knowledge on the Brazilian aplacophorans (Mollusca: Caudofoveata & Solenogastres)

“…Through these comparisons, they noted that species with similar body forms and with sclerites of the same shape occur off the western and eastern Atlantic coasts; these similarities could suggest that these species are sister-groups, sharing the same morphological traits as a result of common ancestry. Corrêa et al (2014Corrêa et al ( , 2018 and Passos et al (2017) can be considered as the only more complete studies made on Brazilian aplacophorans, adding detailed data about the structure of the sclerites and radula, as well as about the external morphology and the bathymetric distribution of caudofoveates from Brazil. In Figure 2, all these species recorded by Corrêa et al (2014Corrêa et al ( , 2018 and Passos et al (2017) are illustrated.…”

Better Alone Than in Bad Company: New Species of Caudofoveate Limifossorid (Mollusca, Aplacophora) Unravels Patterns of Distribution Hidden in the Deep Atlantic

“…In past times, SEM was a tool only for a general characterization in Caudofoveata (Scheltema, 1985(Scheltema, , 1997Scheltema et al, 1994), but more recently it has been used to furnish more complete descriptions (Schander et al, 2006;Ivanov et al, 2009;Saito, 2020), becoming a routine technique for the studies of the Brazilian species (Corrêa et al, 2014(Corrêa et al, , 2018Passos et al, 2018). In such way, apart from the general morphology of the animals, important characteristics of the oral shield, radula and sclerites can be observed.…”

“…The animals were initially observed under stereomicroscopes, and then some were sorted for more detailed analysis using Scanning Electron Microscopy (SEM). The methods employed were the same as the ones of Corrêa et al (2014Corrêa et al ( , 2018 and Passos et al (2018). Because individuals (and specially the smaller ones) are hard to identify through only the general morphology, some of their sclerites were extracted from the trunk by using fine needles, and then placed on slides, air-dried and covered with Entellan and a cover slip for permanent preparations; these slides are also deposited in the respective collections.…”

“…Ubiquitous among the deep-sea organisms, aplacophorans form a molluscan group of particular phylogenetic interest (e.g., Kocot et al, 2011;Smith et al, 2011;Vinther et al, 2012Vinther et al, , 2017Mikkelsen et al, 2018Mikkelsen et al, , 2019, ecological importance (Scheltema, 1987(Scheltema, , 1997Scheltema and Ivanov, 2009), and biogeographical relevance (Scheltema, 1985;Ivanov and Scheltema, 2008;Corrêa et al, 2014Corrêa et al, , 2018Bergmeier et al, 2017Bergmeier et al, , 2019Cobo and Kocot, 2020). They are generally characterized by their wormlike bodies covered by sclerites, and formed by two clades: Solenogastres, which are epifaunal and bear a ventral pedal furrow, and Caudofoveata, whose species are infaunal, without a ventral locomotory organ, and have an oral shield (that is absent in solenogasters).…”

“…In the deep Atlantic Ocean, most reports on caudofoveates are for species from both European or North American waters, and fewer are based on specimens collected in the Southern Hemisphere. For the Brazilian coast (Southwestern Atlantic), in particular, eight species are known: Chevroderma turnerae Scheltema, 1985 recorded by Scheltema (1985) and Ivanov and Scheltema (2008), and Spathoderma bulbosum Ivanov and Scheltema, 2008 by Ivanov and Scheltema (2008); Falcidens targatus Salvini-Plawen, 1992 and F. acutargatus Salvini-Plawen, 1992 studied by Corrêa et al (2014); Claviderma amplum Ivanov and Scheltema, 2008, C. crassum Ivanov and Scheltema, 2008and C. virium Corrêa, Miranda and Passos, 2018 investigated by Corrêa et al (2018); and F. australocaudatus Passos, Corrêa and Todt, 2016 described by Passos et al (2018). Passos et al (2019) have summarized all the records of aplacophorans from Brazilian waters up to that time, pointing out that most of them are from restricted oil-rich areas, there remaining large parts of its coast in which these molluscs were never reported (as its southernmost and northernmost portions), and that there are many other species to be investigated.…”