Leuconidae Sars 1878

West Atlantic Leuconidae gap

Until the present study, there were no proper taxonomic records of family Leuconidae for the Brazilian coast. They appear only in ecological studies, where the specimens were identified only at genus level (Leucon and Eudorella) or only into family (Leuconidae A and Leuconidae B) (Băcescu & Petrescu 1991; Dos Santos & Pires-Vanin 1999; Cristales & Pires-Vanin 2014).

Leuconids occur in all oceans (Watling & Gerken 2023) and are also commonly found in the deep-sea zone (> 200 m) (Heard et al. 2007). Records from the NW Atlantic are from Guiana-Suriname Basin to Greenland coast (Bishop 1981a; 1981b; 1982a; Hansen 1920; Heard et al. 2007; Petrescu & Heard 2010) and in SW Atlantic are restricted to the Argentinian and Uruguayan coast (Petrescu 1991; 1994). With the present study new records of the family go further north in the Brazilian coast until 18°S (Espírito Santo state) and south until 27°S (Paraná state), filling the gap in this area. According to the bathymetric distribution, only Gyneleucon tripedium gen. et sp. nov. (39–53 m) is restricted to shallow water. Eudorella helenae sp. nov. (25–392 m) occurs from shallow water to the upper slope, while Leucon (Alytoleucon) rhuanae sp. nov. (1021–2501 m), Leucon (Crymoleucon) pseudograndidentatus sp. nov. (381–1731 m) and Leucon (Macrauloleucon) watlingi sp. nov. (381–3001 m) occur solely on the slope, being the latter with a wider bathymetric range (Fig. 16). The lack of Leuconidae species records for the Brazilian coast might be explained by taxonomic impediment (Marques & Lamas 2006) or by the depths where leuconids generally live. The group successfully colonized the deep-sea, a difficult to reach and less sampled environment when compared to the continental shelf (Mühlenhardt-Siegel 2005; 2011; Heard et al. 2007).

Cumacean deep-sea records along the Brazilian coast came from two pioneer expeditions in the sixties led by the Woods Hole Institution aboard the N/O Atlantis II along a long transect between Senegal and Recife (200–5000 m) (Jones 1969; 1973; 1974; 1984; Reyss 1975; 1978). Later on, Watling & Gerken (1999) described two new species, Gaussicuma dufresne Watling & Gerken, 1999 (Bodotriidae) and Campylaspides abyssotrucidatus Watling & Gerken, 1999 (Nannastacidae), both collected from the project Marion Dufresne TAAF-MD55 that dredged along the Vitória-Trindade chain (15–5155 m), off Espírito Santo coast.

The Leuconidae records, as well as Cumacea in general, are more condensed to North Africa and Europe in the Eastern Atlantic (Bishop 1981a; 1981b; Jones 1956; Petrescu 1994; Watling 2009), where we noticed more expeditions and specialists working in the group. However, until 2005, only seven species of Leuconidae have been registered in the Southeast Atlantic, all of which were documented by Bishop (1981a, 1981b). Later on, Mühlenhardt-Siegel (2005; 2011a) conducted large taxonomic studies on Leuconidae in the Southeastern Atlantic, specifically in the Guinea Basin, Angola Basin, and Cape Basin, based in the DIVA I expedition, at abyssal depths ranging from 5047 to 5452 meters. A total of 17 new species were described in these works, with the majority belonging to the genus Leucon, followed by Eudorella, Bytholeucon, and the newly discovered genus Afroleucon.

In the present study we describe five new species and a new genus of Leuconidae for the SW Atlantic, but further studies from the area showed that much more new material needs to be described and will appear in near future publications (Brito pers. com.).