Pycnogonida (Arthropoda) from Uruguayan waters (Southwest Atlantic): <br />annotated checklist and biogeographic considerations

Abstract

Records of pycnogonids from Uruguayan waters (south-western Atlantic) include 26 species cited from precise locations, and at least five other species based on unconfirmed records. Nearly half of the species in that fauna belong to the genus Nymphon (12 spp.). Most species (22) come from deep-water and were recorded and described by C. A. Child. Of these, at least twelve species have an extended Antarctic and Subantarctic distribution, showing the influence of these cold waters in the area; three others have a wide deep-sea distribution pattern. Five species are known only from the lower slope and abyssal basin off La plata river: Mimipallene Atlantis and four species of Nymphon. Records from coastal and shelf areas (four species) are poorly documented and should be the focus of future research. Of these, Colossendeis geoffroyi is considered endemic in the Southwest Atlantic between 34ºS and 40ºS, but presents clear Antarctic affinities. A small-sized species living in shallow waters, Pycnogonum cessaci, is here considered as cryptogenic.

Checklist of the marine Bryozoa from Uruguay (Southwest Atlantic)

“…Thirty out of the 73 taxa (41%) are known only from deep waters off the Río de la Plata, with an additional species also known from a station in Patagonian deep waters. Even considering there are some undetermined species, this result shows a high degree of endemism, as it was already shown for several benthic groups such as Bivalvia, Ascidiacea and Pycnogonida (Scarabino et al, 2016(Scarabino et al, , 2018(Scarabino et al, , 2019. Furthermore, also molecular analysis could identify even more endemic species amongst some of the more seemingly widely distributed species.…”

“…The remaining recorded species could be classified in three groups: 1) deep-sea species widely distributed over other basins (15), 2) shelf and deep-sea species of Antarctic and Subantarctic distribution (17), and 3) shelf species, including shallow water cryptogenic or introduced taxa (10). A similar pattern exists concerning the proportion of species for Ascidiacea and Pycnogonida from Uruguayan waters (Scarabino et al, 2018(Scarabino et al, , 2019 and it represents a bias. In fact, most of the species compiled in this study were gathered during two oceanographic cruises that surveyed the continental slope and abyssal plain off Uruguay.…”

Pycnogonida (Arthropoda) from Museu de Ciências Naturais, Rio Grande do Sul, Brazil

“…Circumpolar. Antarctic, Western South America and up to Buenos Aires (Argentina), South Africa, Madagascar, New Zealand, Eastern South America (Child 1995a;Munilla and Soler-Membrives 2009;Scarabino et al 2019). This is the first record for Uruguayan waters.…”

“…Pushkin, 1975: 80-83, fig. Distribution. Antarctic (Ross Sea, Weddell Sea) to southern Argentina (up to approximately 37°15'S), southeast Pacific (Strait of Magellan up to 33°S) (Weis et al 2014;Scarabino et al 2019).…”

“…Literature records large morphological variations for this species (Hoek 1881;Hodgson 1907;Loman 1923;Gordon 1944;Child 1995b;Weis et al 2014). These variations encompass mainly the proportion of the articles of the legs, the shape of the trunk, the structure of the propodus, the size and inclination of the abdomen and the size of the cement gland (Stock 1957;Pushkin 1993;Child 1995b; Cano-Sanchez and López-González 2019; Scarabino et al 2019).…”