Family GNATHIIDAE Leach, 1814

Gnathia campotonotus

© Copyright from Cohen & Poore 1994.

Museums

Regional Maps

• Gnathides Leach, W.E. 1814. Crustaceology. pp. 383-437 in Brewster, D. Sir (ed.). The Edinburgh Encyclopaedia. Edinburgh : John Murray Baldwin & Cradocle Vol. 7 (2). [432] [original spelling].

Introduction

Gnathiids are most unusual isopods, polymorphic in the extreme. Males are immediately recognisable by their large mandibles directed forwards from the cephalosome. The first pereopods are usually modified as ‘pylopods’, operculate and protecting the other mouthparts (Cohen & Poore, 1994). The pereon bears only five pairs of walking legs, pereopod 7 being absent in adults. Males settle after their final instar in crevices in the sediment, mud, submerged wood, sponges, coral rubble or cavities in the reef, do not feed, and may gather a harem of females in their ‘home’ (Tanaka, 2007). Females have more reduced jaws and a thorax swollen with ovary or eggs, sometimes more than a hundred.

Adult gnathiids are marine benthic isopods but the praniza larva is ectoparasitic on fishes. The family is cosmopolitan in coastal to deep-sea environments with numerous species (Monod 1926; Camp 1988). Monod (1926) who studied the biology of this most unusual group of isopods recognised six genera but until recently most were treated in the genus Gnathia.

Holdich & Harrison's (1980) review of the Australian fauna was superceded by that of Cohen & Poore (1994) who described 27 new species from Australia. They also presented a phylogenetic analysis which differentiated ten genera. Although the family has long been regarded as belonging to a separate suborder of the Isopoda, Wägele (1989), Brusca & Wilson (1991) and Dreyer & Wägele (2001) concluded that the family is derived from cirolanid- or cymothoid-like ancestors. More recently, Svavarsson & Gísladóttir (2002) published a list of species, one of them new.

Diagnosis

Males with enlarged head, anteriorly-directed mandibles, pereonite 1 short, fused into cephalosome; pereonite 7 shorter than pereonites 2–6; females with pereon swollen with ovary or embryos. Eyes contiguous or almost contiguous anterodorsally and extending from anterior margin to posterior margin of head (Tenerognathia only), or widely separated, lateral, sometimes small or absent. Mandibles enlarged, projecting anteriorly and together forceps-like. Maxillula usually absent. Pereopod 1 modified as pylopod ventrally overlying mouthparts, pereopod 7 absent as adults. Ectoparasitic, usually on fishes.

General References

Brusca, R.C. & Wilson, G.D.F. 1991. A phylogenetic analysis of the Isopoda with some classificatory recommendations. Memoirs of the Queensland Museum 31: 143-204

Camp, D.K. 1988. Bythognathia yucatensis new genus, new species, from the abyssal depths in the Caribbean Sea, with a list of gnathiid species described since 1926. Journal of Crustacean Biology 8: 668-678

Cohen, B.F. & Poore, G.C.B. 1994. A phylogeny and biogeography of the Gnathiidae (Crustacea: Isopoda) with descriptions of new genera and species, most from south-eastern Australia. Memoirs of Museum Victoria 54: 271-397

Dreyer, H. & Wägele, J.-W. 2001. Parasites of crustaceans (Isopoda: Bopyridae) evolved from fish parasites: molecular and morphological evidence. Zoology (Jena) 103: 157-178

Holdich, D.M. & Harrison, K. 1980. The crustacean isopod genus Gnathia Leach from Queensland waters with descriptions of nine new species. Australian Journal of Marine and Freshwater Research 31: 215-240

Monod, T. 1926. Les Gnathiidae. Essai monographique (Morphologie, Biologie, Systématique). Mémoires de la Société des Sciences nat. Physique du Maroc 13: 1-668

Svavarsson, J. & Gísladóttir, E. 2002. Elaphognathia korachaensis sp. nov., a new gnathiid species (Crustacea, Isopoda) from Thailand. Phuket Marine Biological Center Special Publication 23: 157-164

Tanaka, K. 2007. Life history of gnathiid isopods–current knowledge and future directions. Plankton & Benthos Research 2: 1-11

Wägele, J.W. 1989. Evolution und phylogenetisches System der Isopoda. Stand der Forschung und neue Erkenntnisse. Zoologica (Stuttgart) 140: 1-262

History of changes