Platorchestia platensis C. S. SEREJO

Figs 25–26

Platorchestia platensis.– Stock, 1996: 153, Figs 2D, 3D; Jo, 1988: 166, fig. 8; Miyamoto & Morino, 2004: 81: fig. 7; Serejo, 2004: 19: fig. 10.

Material examined. Type material of Orchestia platensis Krøyer, 1854, PARALECTOTYPES: male, 6.8 mm, female, 7.6 mm, ZMC CRU7803, Rio de la Plata, Montevideo, Uruguay.

Diagnosis. Outer plate of maxilla 2 with pectinate setae. Male antenna 2 and pereopod 7 strongly sexually dimorphic. Carpus of pereopod 7 incrassate, laterally elliptic. Male gnathopod 1 cuspidactylate. Male gnathopod 2 with palm sinuous, lacking conspicuous notch; dactylus not narrowing distally. Coxa 6 posterior lobe with anterodistal corner subquadrate, with process, 1–3 marginal setae, posterior margin perpendicular to ventral margin. Pleopod 1 lacking marginal setae. Pleopod 2 with 4 median marginal robust setae; pleopod 3 with 4 median marginal robust setae. Coxal gills convoluted or simple. Pereopods 3–5 gills smaller than gills 2 and 6. Oostegites 2–4 moderately setose (around 20 setae). Oostegite 5 with 9 setae, posterior margin with fewer setae than anterior margin.

Remarks. Considering the similarity of P. platensis with P. paraplatensis n.sp. herein described, other characters, based on the lectotype, such as shape of coxa 6, oostegite 5 setae, and number of setae on pleopods of the former species were observed and used to differentiate these taxa as discussed above. Recent studies on Platorchestia, including P. platensis, were based on material from Europe (Jo, 1988; Miyamoto & Morino, 2004), despite the fact that the type locality of this species is Montevideo, Uruguay. Small differences were noted when comparing the type material with some European redescriptions of P. platensis, such as the dactylus of gnathopod 2, which is narrowing distally in material from Kent, England (Miyamoto & Morino, 2004) (versus not narrowing), the palm of gnathopod 2, which is notched (versus sinuous), and the dactylus of gnathopod 1 in Denmark specimens (Jo, 1988), which fits the palm (versus shorter). As new characters of the P. platensis complex come to light it is important for future studies on the group to show clearly the diagnostic features noted herein for an accurate assessment. For the time being, we consider the European species as P. platensis, although a careful examination from the southern population of Montevideo with the European specimens may prove that we are dealing with different taxa. Genetic studies would be helpful in this case.