Pallenopsis Wilson 1881

Genus Pallenopsis Wilson, 1881

Remarks: This genus has a long and complex taxonomic history in the southwest Atlantic, summarized by Stock (1973, 1975). Weis et al. (2014) analysed the existence of a species-complex within the traditional concept of Pallenopsis patagonica (Hoek, 1881). In fact, they referred it as “one of the most taxonomically problematic and variable pycnogonid species known to date”.

Böhm (1879) recorded Pallenopsis fluminensis (Kroyer, 1844) (as Phoxichilidium fluminensis) from the Magellan Strait and Patagonia (54.9–76.8 m depth) based on material collected by the RV Gazelle in 1876, deposited in the Museum für Naturkunde der Humboldt-Universität zu Berlin. In the zoological report of the Gazelle expedition, Studer (1889) recorded that species (as Pallene fluminensis) from three stations, adding a third and deeper (80.5 m) record from the Uruguayan shelf. Schimkewitsch (1930) considered that Böhm’s specimens represent a new species: Pallenopsis boehmi. Stock (1973) redescribed this species, re-examining the material identified by Böhm as P. fluminensis (four specimens collected by the Gazelle), but considered that one specimen belongs to P. patagonica. Stock (1973) nominated a female specimen from the Magellan Strait as the Lectotype of P. boehmi. Due to insufficient labelling, it was not possible to establish which locality the specimen of P. patagonica belongs; either it was station LVII, 38°10.1´S– 56°26. 6´W, 54.9 m depth, off Buenos Aires Province, Argentina, or it belongs to station LX, 34°43.7´S– 52°36.1´W, 80.5 m depth, Uruguayan shelf (Stock 1973; Dunlop et al. 2007). Therefore, the records of Studer (1889) for both localities remain uncertain. According to Stock (1973, 1992), P. boehmi has a geographical distribution extending from the Strait of Magellan to southeast Brazil (ca. 23°10´S). This distribution is biogeographically anomalous for a shelf species.

Pallenopsis tumidula Loman, 1923 was recorded from the RV Calypso 1961 –1962 cruise station 172 off Buenos Aires Province, Argentina by Stock (1966). Another specimen, from an unknown location due to mixing of materials, was collected at one of the following stations of the same expedition: 160, 161 (both in Uruguayan waters), 171 or 173 (off Buenos Aires Province, Argentina) (Stock 1966). Stock (1992) also reported this species for southeast and south Brazil (23°15´S– 30°20´S); therefore, the Uruguayan shelf is within its geographic range, although there are no reliable records. Station 2 of the 1901–1903 Swedish Antarctic Expedition (off Buenos Aires Province, Argentina, 37°30´S– 56°11´W, 100 m) is the type locality of P. tumidula (Loman 1923).

Hedgpeth (1943) recorded, for the first time, P. fluminensis for Argentinean waters, off Buenos Aires Province (37°42'S– 56°20'W, 80.4 m depth, station 26 of Hassler Expedition). Later, Bremec et al. (1986) briefly described and illustrated one specimen of Pallenopsis collected in the littoral zone of the Buenos Aires Province (38°45´S), identifying it as P. fluminensis. This species is otherwise known from the Brazilian coast (Lucena et al. 2017).