Australian Isopoda: Families

S.J. Keable, G.C.B. Poore & G.D.F. Wilson

Plakarthriidae Hansen, 1905 (1887)

Chelonidiidae Pfeffer, 1887: 85.

Plakarthriinae Hansen, 1905a: 100.

Plakarthriidae. -Poore & Brandt, 2001: 374.

Description. Body. Body shape without loss or gross modification of appendages on one side of the body; in dorsal view strongly dorsoventrally compressed, coxae splayed laterally, smoothly ovate in outline, expanded peduncular articles of antenna 1 and 2 helping to define ovate outline.

Head. Head not capable of lateral rotation (laterally encompassed, abutting or fused to pereonite 1). Eyes widely separated and small, or absent. Antenna 1 inserting on head anteriorly and/or dorsally to antenna 2, minute or well developed; not as follows: reduced to 2 articles with second article expanded and scalloped. Antenna 2 well developed. Mouthparts not forming suctorial cone or proboscis. Mandible not projecting anteriorly and together forceps-like; palp absent. Maxilliped palp medial margin recurved spine-like robust setae absent; endite conspicuous.

Pereon. Pereonites 6-7 pereonite 7 distinct dorsally, free. Coxae extending ventrally and laterally to overhang the coxa-basis articulation of the pereopods. Coxa 1 and pereonite 1 distinctly separated by suture line. Pereopods 6-7 pairs readily apparent; 1-3 or 1-7 not prehensile. Pereopods 5-7 without flattened setose articles andor dactyls modified or absent.

Pleon / Pleotelson. Pleonites and pleotelson with pleonites 1-5 fused with conspicuous lateral sutures, pleotelson fused to pleonites 1-5, or pleonite 1 unfused, pleonites 2-5 fused with partial (usually lateral) sutures, pleotelson wholly or partly fused with pleonites 2-5. Pleopods 5 pairs present. Pleopod 2 of males not consisting of an enlarged peduncle with a geniculate endopod and a small muscular exopod. Uropods positioned proximally on pleotelson, or positioned distally on pleotelson; distinct from pleopods, not forming operculum over pleopodal chamber (although may be folded ventrally below pleotelson). Peduncle not forming an elongate clavate article with rami reduced or absent; not fused to endopod. Rami inserting on peduncle adjacent to each other. Endopod present, not claw-like (acute and recurved) andor posteroventral in position. Exopod not folded dorsally over pleotelson.

Remarks. Plakarthriidae Hansen (1905) is a replacement name for Chelonidiidae Pfeffer (1887) and should be cited as Plakarthriidae Hansen, 1905 (1887), see Poore & Brandt (2001) and Martin & Davis (2001).

Distribution and generic composition. Monogeneric with three species (See Kensley et al. (1996)). Plakarthrium puctatissimum occurs in the shallow sublittoral of islands in the Bellinghausen Sea, along the western side of the Antarctic peninsula and northward to South Georgia (Wilson et al., 1976); P. typicum occurs in New Zealand (Wilson et al., 1976); P. australiense occurs in southern Australia from central Victoria to southern Western Australia and Tasmania in depths of 6-49m, on Amphibolis, Ecklonia holdfasts and red algae (Poore & Brandt, 2001).

Cite this publication as: 'S.J. Keable, G.C.B. Poore & G.D.F. Wilson (2002 onwards). 'Australian Isopoda: Families. Version: 2 October 2002.'.