The sea cucumber Psolus patagonicus (Echinodermata: Holothuroidea) from the southwestern Atlantic: Redescription of the holotype and a new synonym

Psolus patagonicus Ekman, 1925 is redescribed from material including the holotype, deposited in the Zoologisches Museum Hamburg (ZMH), and specimens of the Museo Argentino de Ciencias Naturales “Bernardino Rivadavia” (MACN-In). Psolus marcusi Tommasi, 1971 is stated as a junior synonym. Since also the specimens used by Ludwig in 1897 to report the brooding behavior of Psolus antarcticus (ZMH: E4168) are identifiable as P. patagonicus, the latter is the only South American psolid holothuroid known to be a brooder.

. Psolus patagonicus Ekman, 1925. Holotype: ZMH E4173, dorsal view. Scale bar: 1 cm. Tommasi, 1971: 4. Psolus antarcticus: Ludwig, 1897(non Philippi, 1857. Description: Psolid shape, up to 23.26 mm long, color in life light orange to white; in alcohol, white. Mouth and anus dorsal, covered by five valves and five interradial teeth between the valves. Valves and interradial teeth in anus about half size of mouth pieces (Fig. 1). Tentacles 10, white with brown dots, eight dendritic and the last two (most ventral) reduced, bifid-ended (ratio 1:3). Tube feet up to 0.35 mm in diameter, only on ventral side; trivium with central ambulacra naked, and both lateral ambulacra with one zig-zag and two rows of podia. Calcareous ring simple, with five radial and five interradial pieces fused at the base. Radial piece with an anterior notch and anteriorly wider than the interradial piece, which has not notch. One Polian vesicle in the left ventral side, one stone canal and a twokidney shaped madreporite, attached to the base of the middorsal interradial piece. Gonad on the dorsal side, below the calcareous ring, composed by multiple tubes, well developed during reproductive season. Respiratory trees well extended up to the anterior part of the body, right trunk longer than the left one.

Remarks:
In some specimens with retracted tentacles, the oral and anal valves may cover the oral and anal interradial teeths, which could not be seen. According to Pawson (1964) teeths could be absent in small specimens.

DISCUSSION
The original description of Psolus marcusi Tommasi, 1971, based on a single specimen 11 mm long, noted the absence of oral teeth as the only difference to P. patagonicus (Fig. 1, 4) with no comparison to the sympatric psolid, Psolus patagonicus. The specimen described by Tommasi was deposited at the Museu de Zoologia da Universidade de São Paulo (Tommasi,personal Fig. 3. Psolus patagonicus Ekman, 1925. Ossicles: A. Plates from the ventral side, B. Curved plates from podia, C. Curved plates from tentacles. Scale bar: 100 μm. Tommasi, 1971. Drawings from Fig. 9 and 10 of Tommasi (1971). A. lateral, B. dorsal, C. ventral view, D-E. plates, F-G. curved plates with multiple perforations. communication), but no such material could be traced in that collection, so I conclude that the holotype of Psolus marcusi is lost.

Fig. 4. Psolus marcusi
Since the oral and anal teeth of Psolus patagonicus may be easily overlooked when they are covered by the oral and anal valves, and Pawson (1964) pointed out that oral teeth could be absent in small specimens (up to 11 mm, i.e. the size of the holotype of P. marcusi), there is no evidence of any meaningful difference between these two sympatric taxa. So I conclude that P. marcusi Tommasi, 1971 is a junior synonym of P. patagonicus Ekman, 1925.
Ludwig (1897) reported a brooding behavior for Psolus antarcticus (Philippi, 1857). This report did not include any collection number. However, the specimens E4168 from the ZMH collection, which are coincident in locality, collector and date with the material mentioned by Ludwig as P. antarcticus, were labeled as P. patagonicus by Power in 1965, and this identification is confirmed herein. Therefore, Ludwig's (1897) report on brooding actually referred to P. patagonicus before its original recognition as a different species by Ekman (1925). Since there are no other reports on P. antarcticus brooding behavior after Ludwig's observations, and the identification of his specimens was rectified, the only brooder psolid up to now properly described for South America is P. patagonicus.