The sea cucumber Echinopsolus murrayi Théel, 1886 n. comb. (Echinodermata: Holothuroidea) from the southwestern Atlantic, redescription of the holotype and description of new specimens

: Psolus murrayi Théel, 1886 was one of the multiple species described from the specimens collected by the HMS Challenger Expedition. This species was placed in Psolus , genus with dorsal scales. Among holothuroids, there are some taxa that have a dense presence of dorsal ossicles, which gives them a psolid-like appearance. From the presence of different ossicles and the absence of scales on dorsal side, we here redescribe the species now, known as Echinopsolus murrayi (Théel, 1886) n. comb. This species has dorsal warts full of ossicles, ten tentacles and rectangular sole with three rows of podia. Body wall ossicles are plates and cups, and multilayered plates exclusively on dorsal body wall. For tentacles and podia, ossicles are curved and straight perforated bars.

moved in several species (from different genera) to Echinopsolus after finding many characteristics in common. These characteristics were integrated into the diagnosis of the genus: all gonochoric; a genital papilla is present on the oral disc, females brood their offspring in five anterior interradial brood pouches; multiple spermatozoa always bundled to bunch-like spermato-zeugmata and spermatozoa with a fusiform head and a hollow cylinderlike mid-piece encircling the anterior end of the flagellum. Those species were Echinopsolus charcoti (Vaney, 1906), Echinopsolus koehleri (Vaney, 1914), Echinopsolus mollis (Ludwig & Heding, 1935), Echinopsolus splendidus (Gutt, 1990), Echinopsolus acutus (Massin, 1992). In addition, Massin (1992Massin ( , 2010, describe two species for the genus, Echinopsolus parvipes Massin, 1992 East Weddel Sea and Echinopsolus excretiospinosus (Massin, 2010). Recently Panina et al. (2020) redescribed the genus and describe two new species, Echinopsolus sanamyanorum Panina, Stepanov, Smirnov &Martynov, 2020 andE. onekotanensis Panina, Stepanov, Smirnov &Martynov, 2020. From the ten species of Echinopsolus, almost all of them are from Antarctica, except from E. sanamyanorum and E. onekotanensis, which both are from Kamchatka Peninsula area. All these references give us information to identify other Echinopsolus species and spotlight that may be several other species, could be included in this genus. New material have been collected in three cruises in the deep-sea of the southwestern Altantic, Talud I, II and III, between 2012 and 2013. One of the species collected was Psolus murrayi (Theel 1886). This study is the first redescription, since Théel´s work, with new material collected near the type locality site.

MATERIAL AND METHODS
Specimens were collected after the Talud Continental cruises (2012-2013) onboard the B/O Puerto Deseado using dredge trawlers and fishing nets, in the area of the Mar del Plata submarine canyon. All the specimens were preserved in ethanol 96%, analysed and dissected under a stereomicroscope. Digital photos of the specimens were taken using a Canon PowerShot SX110. The ossicles were digitalised using a Zeiss Axio Imager Z1 microscope with an Axiocam HRc digital camera and Axiovision software. The specimens collected, were compared with the type specimen, from the Natural History Museum of UK(NHMUK) and based on the diagnosis made by Theel (1886). New specimens of this species were deposited at the Museo Argentino de Ciencias Naturales Bernardino Rivadavia (MACN).

DISCUSSION
The samples collected enlarge greatly the amount of samples of Echinopsolus murrayi n. comb., until now with only one specimen. The specimens collected have the same diagnostic features of the type species (NHMUK 1886.10.2.87), dorsal warts, ten tentacles and rectangular sole with three rows of podia among other characters. In addition, the specimens herein were found near the type locality. The ossicles, also match with the one observed by Théel (1886), which are cups and multiperforated plates. Here we are also describing straight and curved bars from tentacles and podia. This species was also reported by Ludwig & Heding (1935) for Bovet Island (54°29'S, 3°43'W) at 567 m. According to the reference, these specimens have not podia in the middle ambulacra and five valves which are an important difference with the holotype described by Théel (1886) and the specimens studied herein. Because of this and the huge difference observed for the locality, these specimens are not E. murrayi. A proper study, focus on these specimens will determine if they are members of Echinopsolus or not.
All the specimens studied lack dorsal scales which indicate that this species does not belong to Psolidae. Théel (1886) observed a dorsal side with multiple warts and cup ossicles, like the one observed herein. The dorsal warts full of ossicles could lead Théel (1886), to misjudge this character with the dorsal scales from Psolus. Although this similarity and other characteristics among Psolus and Echinopsolus are still on-going work (see Bohn & Hess 2014, Panina et al. 2020. In comparison with other Echinopsolus, E. murrayi and E. acanthocola has also dorsal processes with a heavy skeleton and no podia. These characters are quite diagnostic, and enable to separate these two species from their cogeneric. E. acanthocola has the ventro-lateral rows, joint on the posterior region and a few tube-feet on middle radii, in contrast with E. murrayi which has three clear and separate rows. In addition, E. murrayi has bars and cups, these ossicles are not present on E. acanthocola. Also, this species has multilayered plates on body wall, tube-feet and tentacles, in contrast with E. murrayi that has multilayered plates only in dorsal body wall.
The genus Echinopsolus has been associated with Antarctic waters (Bohn & Hess 2014). The specimens found in this work came from the Mar del Plata submarine canyon area and it is the first species of this genus, off Argentina. Several reports have registered Antarctic currents, the Antarctic Intermediate Water (AAIW) and the Upper Circumpolar Deep Water (UCDW). These currents flow from south to north between 1000-2000 m in the area of the Mar del Plata submarine canyon , Voight et al. 2013. The deep range in which the specimens were found (1097-1398) could indicate how this species appear northern than the co-generic, and north of the Circumpolar Current which has been indicated to be an important barrier for several invertebrates (O´Loughlin et al. 2011). In addition, previous reports indicated the association between the Mar del Plata submarine canyon area and Antarctica (Martinez & Penchaszadeh 2017, Martinez et al. 2019. It is still a clue the association among these species and those from Kamchatka Peninsula area. Perhaps future steps could be focus on stablish if it is or not and association. One male specimen observed has a genital papillae in between the dorsal pair of tentacles. According to Panina et al. (2020), this is not a diagnostic character for Echinopsolus, although several species of the genus have it, and reinforce the change of genus made it herein. The female specimens observed, have not broods or any evidence of brood pouches or sacs/ pockets, which have been reported for several species of Echinopsolus. The low number of specimens analyzed here, is not enough to discharge the idea about brooding on this species.