Tommasi (1971) erected Psolus marcusi upon a single specimen 11 mm long caught at 95 m off the coast of Mar del Plata, 38°05'S, 55°48'W (Argentina). No reference was made in the original description as to where the holotype of P. marcusi was deposited. After Tommasi’s retirement, his collections were donated to the MZUSP or were dispersed (mostly the ophiuroids) among multiple Brazilian institutions (see remarks under P. vitoriae).
Martinez (2016) was unable to locate the holotype of P. marcusi at MZUSP or MACN (Argentina). Our attempts to locate it at MZUSP and in other Brazilian repositories (IB/UFRJ, MNRJ, UNESP, ZUEC) were also unsuccessful and we agree with Martinez (2016) that the holotype of P. marcusi should be considered to be lost.
Based on Tommasi's (1971) morphological account and illustrations alone, Martinez (2016) placed P. marcusi under the synonymy of P. patagonicus Ekman, 1925, a species originally described upon a single specimen 20 mm long, caught at 110 m in the Patagonian Bank (46°S), and since reported from several additional localities along the Argentinean coast and from near the Strait of Magellan, 48°S (Hernández, 1981; Martinez, 2016).
We believe that the proposed synonymy of P. marcusi with P. patagonicus deserves further investigation.
According to Martinez (2016: 239) "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...". However, an absence of oral teeth was never reported by Tommasi (1971) for P. marcusi, nor used to support P. marcusi as a new species.
In fact, Tommasi (1971) never compared P. marcusi with P. patagonicus. It appears that Tommasi's (1971) omission to report on the oral teeth was interpreted by Martinez (2016) as evidence of absence of oral teeth in P. marcusi.
Martinez (2016) also stated that "Since the oral and anal teeth of Psolus patagonicus may be 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." However, Pawson (1964: 463) was actually referring to the "smaller plates" "near the base of the oral valves" in P. patagonicus and not to the oral and anal teeth.
Furthermore, according to Tommasi's description and illustrations of the holotype, the sole in P. marcusi is provided with smooth plates, not knobbed ones (Tommasi, 1971: Fig. 10C–D), whereas Martinez's (2016: fig. 2A) illustrations of P. patagonicus clearly show several knobbed sole plates. It is not clear whether Martinez's illustrations of the sole ossicles are from the holotype of P. patagonicus or from non-type material from Argentinean waters.
Martinez (2016) considered the original description of P. marcusi adequate, even though it is extremely brief and the supporting illustrations very poor. Tommasi (1971) described the existence of cups in the body wall ("... Com corpúsculos calcáreos do tipo "taças"...), but his figures clearly show curved plates instead of cups thus contradicting his own description (Tommasi 1971: 4, figs. 10a–b).
Clarifying the status of Psolus marcusi Tommasi, 1971 will require access to morphological details not available from the extremely brief and imprecise original description. The morphological details of the calcareous ring, a character complex useful for distinguishing among Psolus species (this paper), has not been studied in P. marcusi. Evaluation of the validity of P. marcusi thus awaits the availability of material that matches Tommasi’s limited description.