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

Abstract

Aplacophorans are common inhabitants of the deep-sea, where many places remain unexplored regarding their biodiversity. Filling a gap in knowledge about these animals from the South Atlantic, Scutopus variabilis sp. nov. (Caudofoveata, Limifossoridae) is described; further, species distribution modelling (SDM) was performed to elucidate the distribution patterns of Atlantic species of Scutopus. The type materials of S. megaradulatusSalvini-Plawen (1972) and S. chilensisSalvini-Plawen (1972), were examined and a search was performed for specimens of Scutopus held in museum collections. Scutopus variabilis sp. nov. has a slender and highly variable body form and a very distinct suture line is present midventrally. Two dominant types of trunk sclerites were observed by Scanning Electron Microscopy (SEM): one elongated with lateral margins slightly concave in medial portion, and another longer, with narrower base; its radula bears up to eight rows of heavily sclerotized teeth bearing 12–16 small denticles. The species occurs in a wide bathymetric range (40–1300 m), being more abundant at the edge between the continental shelf and upper slope. Outside the areas from where these samples were obtained, suitable areas for S. variabilis sp. nov. were found in the Southern Caribbean Sea (from where S. megaradulatus is recorded) and in the Brazilian Northern coast; the Gulf of Mexico and the Brazilian Northeastern coasts were found as unsuitable. Species of Scutopus appear to exhibit different patterns of geographical distribution: the European S. ventrolineatusSalvini-Plawen (1968) and S. robustusSalvini-Plawen (1970) are known as widely distributed, while non-European representants, the American S. megaradulatus, S. chilensis and S. variabilis sp. nov., and the Japanese S. schanderiSaito and Salvini-Plawen (2014) and S. hamatamiiSaito and Salvini-Plawen (2014) have more restricted distributions. However, clear and definite patterns of distribution of some of these species are probably blurred by sampling bias, for the European area is better studied. In the Atlantic, the SDM showed that species of Scutopus occur in a way that overlapping is minimized. Great sampling efforts combined with detailed descriptions based on SEM have revealed an interesting, abundant and up to now undescribed Brazilian deep-sea malacofauna.

Cambrian ‘sap-sucking’ molluscan radulae among small carbonaceous fossils (SCFs)

“…1 a of [ 50 ]), as well as the radulae of certain limifossorid aplacophorans (e.g. Scutopus variabilis [ 51 ]) and Solenogastres (fig. 11 b , d of [ 52 ], fig.…”

“…Nevertheless, the teeth in these compound forms differ from the blade-shaped morphologies found in the SCFs (and in the radulae of sacoglossans), and instead comprise various spade-shaped or hook-shaped teeth adapted to scraping, often bearing prominent denticles (fig. 4 of [ 51 ]). Taphonomic flattening aside, the SCF tooth blades also appear to comprise a single type, and are oriented perpendicular to the base ( figure 2 ) as seen in the tooth arcs of uniseriate radulae ( figure 3 ).…”

Caudofoveata ("Mollusca, Aplacophora") do Atlântico Ocidental

“…No caso do Oceano Atlântico Ocidental, especificamente, a costa leste dos Estados Unidos foi amplamente estudada, com 16 espécies descritas (e. g. HEATH, 1918;SCHELTEMA, 1972SCHELTEMA, , 1973SCHELTEMA, , 1981SCHANDER et al, 2006). Outras áreas, como o Golfo do México -9 spp descritas (IVANOV & SCHELTEMA, 2007, 2008; a Bacia da Guiana -8 spp espécies (IVANOV & SCHELTEMA, 2008) e a costa sudeste brasileira -7 spp (CORRÊA et al, 2014(CORRÊA et al, , 2018PASSOS et al, 2018PASSOS et al, , 2021, são consideradas como "razoavelmente" estudadas, com registros mais completos de algumas espécies e famílias. Já as regiões da Bacia Argentina, com 6 espécies FORCELLI, 2000;, Mar do Caribe (SALVINI-PLAWEN, 1972 e nordeste brasileiro, ambos com 2 espécies descritas podem ser consideradas como "pouco" conhecidas contendo apenas registros pontuais de espécies.…”

“…e Psilodens sp. (TREECE, 1979;PASSOS et al, 2021). No Brasil, a costa sudeste concentra um número muito maior de espécies ( 7espécies (CORRÊA et al, 2014(CORRÊA et al, , 2018PASSOS et al, 2018PASSOS et al, , 2021 quando comparado litoral do sul e nordeste, cada um com uma única espécie registrada até o momento PASSOS et al, 2021).…”

“…(TREECE, 1979;PASSOS et al, 2021). No Brasil, a costa sudeste concentra um número muito maior de espécies ( 7espécies (CORRÊA et al, 2014(CORRÊA et al, , 2018PASSOS et al, 2018PASSOS et al, , 2021 quando comparado litoral do sul e nordeste, cada um com uma única espécie registrada até o momento PASSOS et al, 2021). E mesmo na costa sudeste brasileira, é possível que 11 espécies de caudofoveados ainda estejam esperando uma descrição mais formal na Bacia de Campos (CORRÊA et al, 2014), além de registros incompletos de Limifossor sp.…”