Family PLAKARTHRIIDAE Hansen, 1905

Plakarthrium australiense

© Copyright from Poore & Brandt 2001.

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• Plakarthriinae Hansen, H.J. 1905. On the propagation, structure and classification of the family Sphaeromidae. Quarterly Journal of Microscopical Science 49: 69-135 [115] [original spelling; subfamily of Sphaeromatidae].

  Type genus:

   Plakarthrium Chilton, 1883.
• Chelonidiidae Pfeffer, G. 1887. Die Krebse von Süd-georgien nach der Ausbeute der deutschen Station 1882–83. I. Teil. Jahrbuch der Hamburgischen Wissenschaftlichen Anstalten 4: 41-150 [85].

  Type genus:

   Chelonidium Pferrer, 1887.

Taxonomic Decision for Synonymy

• Poore, G.C.B. & Brandt, A. 2001. Plakarthrium australiense, a third species of Plakarthriidae (Crustacea: Isopoda). Memoirs of Museum Victoria 58: 373-382 [374] (Pfeffer’s (1887) generic name Chelonidium is a junior synonym of Plakarthrium Chilton, 1883. Plakarthriidae (erected by Hansen (1905) as Plakarthriinae, a subfamily of Sphaeromatidae Latreille, 1825) is the family name used by most authors and, under ICZN (1999) Article 40, replaces Pfeffer’s (1887) family name, Chelonidiidae.)

Introduction

Plakarthriids are epizoans on large shallow-water algae. They are flattened, almost limpet-like inhabitants of shallow macroalgal communities. They are unique in that the margin of the body is defined entirely by flattened limbs, antennulae, antennae, pereopodal coxae and uropods. The head is free from pereonite 1 and, unlike most isopods, the first coxal plate is free from the pereonal tergite. The family is known from only three species of Plakarthrium, one on the Antarctic Peninsula, South Georgia Is. and Chile, a second in New Zealand, and the third in southern Australia. The similarities of this small family to other Flabellifera were discussed by Wilson et al. (1976) who could not decide on its affinities. Poore & Brandt (2001) thought an affinity with cassidiniine sphaeromatids likely. Surprisingly, Wetzer et al (2013) found Plakarthrium (Plakarthiidae) is nested within the Sphaeromatidae.
in most analyses.

Diagnosis

Body oval, flat, margin defined by plates of antennulae, antennae, coxae and uropods; head free from pereonite 1; pereonites 1–7 visible dorsally, separated by sutures. Coxal dorsal plates 1–7 delimited from tergite by suture; plate 7 expanded posteriorly, similar to coxal plate 6, visible dorsally. Pleotelson rectangular, flattened, pleonites 1, 2 fully or laterally demarcated, enclosed by coxae 7 laterally, uropods attached posteriorly. Antennular and antennal peduncles laminar, defining margin of body. Mandibular incisor with 2 blunt teeth; molar process absent. Maxillula with single endite, with 7 terminal stout setae. Maxilla with single endite, with 8 terminal stout setae. Maxillipedal palp of 5 free articles. Pereopod 1 ambulatory, palm with few setae. Pereopod 2 not sexually dimorphic. Pleopods 1–3 peduncles subquadrate, with terminal rami. Uropods attached on posterior margin of pleotelson; biramous, contiguous, terminal.

General References

Poore, G.C.B. & Brandt, A. 2001. Plakarthrium australiense, a third species of Plakarthriidae (Crustacea: Isopoda). Memoirs of Museum Victoria 58: 373-382

Wetzer, R., Pérez Losada, M. & Bruce, N.L. 2013. Phylogenetic relationships of the family Sphaeromatidae Latreille, 1825 (Crustacea: Peracarida: Isopoda) within Sphaeromatidea based on 18S-rDNA molecular data. Zootaxa 3599: 161-177

Wilson, G.D., Thistle, D. & Hessler, R.R. 1976. The Plakarthriidae (Isopoda: Flabellifera): déjà vu. Journal of the Linnean Society of London, Zoology 58: 331-334

History of changes