Platypyga, Wilson & Keable, 2002

Wilson, George D. F. & Keable, Stephen J., 2002, New Genera of Phreatoicidea (Crustacea: Isopoda) from Western Australia, Records of the Australian Museum 54 (1), pp. 41-70: 60

publication ID 10.3853/j.0067-1975.54.2002.1359

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Platypyga   n.gen.

“New Genus 4” Wilson & Johnson, 1999: 265, fig. 1.

“New Genus X4” Wilson & Keable, 2001, table 1.

Type species. Platypyga subpetrae   n.sp.

Etymology. Platypyga   is derived from the Greek words meaning “flat rump”, which refers to the flattened posterior margin of the pleotelson.

Diagnosis. Body dorsal surfaces pitted especially on head, lacking elongate setae. Head lacking cervical groove. Pleotelson posterior margin with broad reflexed medial region, compressed toward anterior and dorsal margins, medially cleft, forming curved ridge between widelyseparated dorsal projections, each with large robust setae; postanal ridge narrow, with fine setae. Pereopods V–VII with dorsal ridge plates narrower than basis shaft. Pleopod I protopod with coupling hooks. Uropod protopod ventral ridge with rows of laterally projecting long simple setae; dorsomedial plate absent; distoventral robust setae lacking denticles. Uropod rami distally rounded, with apical elongate robust setae.

Remarks. We homologise the unusual pleotelson posterior margin of Platypyga   n.gen. with the cleft medial lobe found in Synamphisopus   and Phreatomerus   . Although we are uncertain, assuming that the two widely spread lobes are homologous to the medial lobe of the other taxa appears to be the simplest explanation. Thus, the small setose bumps on lateral margin just above the uropodal insertions may be homologous with the lateral lobes of other taxa. The posterior margin in Platypyga   , however, lacks any definite demarcation between the larger, more dorsal lobes and this group of setae. Other taxa have groups of setae above the uropods, complicating this interpretation. Because of this uncertainty, we have not scored Platypyga   as having lateral lobes. If, however, the dorsolateral pleotelson lobes of Platypyga   are homologous with lateral lobes, phylogenetic analysis (research in progress) might place this taxon among the Phreatoicidae   , despite its lacking phreatoicid mandibular (pedunculate spine row, absent right lacinia mobilis) and appendix masculina (generally rod-like) synapomorphies. This placement occurs because, unlike many amphisopodids, Platypyga   also lacks a large dorsomedial plate on the uropodal protopod. The generalised appendix masculina of Platypyga   (concave in proximal cross section, acutely rounded distally with a fringe of setae) is similar to other amphisopodids such as Eremisopus   and Peludo   , and may represent a plesiomorphic condition for the suborder. Consequently, Platypyga   appears to have has a unique mixture of plesiomorphic and apomorphic features.