(restricted synonymy and bibliography)
Leptognathiidae Sieg, 1973: unpublished, but see Sieg, 1976. Sieg, 1976: 185, 194. Leptognathiidae subfamily Leptognathiinae: Sieg, 1986 b: 110.
Anarthruridae Lang, 1971 subfamily Leptognathiinae: Sieg, 1986 a, 21, 44. Gutu & Sieg, 1999: 384. Leptognathiidae Sieg, 1973 [revised]: Larsen & Wilson, 2002: 2, 13. Larsen & Shimomura, 2007: 14.
Genera included (Japanese and Kurile-Kamchatka genera in bold): Biarticulata Larsen & Shimomura, 2007; Forcipatia Larsen & Shimomura, 2007; Leptognathia G.O. Sars, 1882.
Diagnosis (after Larsen & Shimomura 2007). Female. Medium body calcification. No plates in carapace. Eyes and eye-lobes absent. Pereon with six free pereonites; pereonite 1 not reduced. Pleon with five free pleonites, as wide as pereon; articulated setae on pleonites absent. Antennule four-articled. Antenna five or sixarticled, article 3 without spiniform setae dorsally. Molar process of mandible pointed. Labium with one pair of lobes, medial spiniform setae absent. Maxilliped bases fused, endites not fused, narrower than basis, without setose or serrated anterio-lateral corners, flat setae or denticles. Cheliped slender and attached via sclerite, fixed finger and dactylus elongated or simple. Pereopod coxae present or absent on pereopods 1–3 but always absent on pereopods 4–6; dactylus and unguis of pereopods 4–6 not fused. Pleopods well developed or absent. Uropodal endopod two-articled, exopod one or two-articled. Marsupium of four pairs of oostegites.
Preparatory male. Generally as above but antennule thicker and pleon and pleopods more well-developed.
Natatory (terminal) male. Body significantly shorter than female. Pereonites less, pleonites more developed than in female. Antennule seven-articled, densely packed with aesthetascs. Mouthparts reduced. Cheliped not enlarged. Pleopods well developed.
Remarks. As has happened with the Family Anarthruridae (Bird 2004), the Leptognathiidae has undergone considerable changes since its establishment by Sieg (1973). Major revisions occurred through Sieg’s (1986 a, b) appraisal of pereopod setation and more recently as an outcome of a controversial phylogenetic analysis by Larsen & Wilson (op.cit.); included genera fell from nine (Exspina Lang, 1968; Leptognathia; Leptognathiopsis Holdich & Bird, 1986; Mirandotanais Kussakin & Tzareva, 1974; Pseudoleptognathia Sieg, 1986 b; Pseudoparatanais Sieg, 1973; Robustognathia Kudinova-Pasternak, 1989; Subulella Holdich & Bird, 1986 and Tanaopsis G.O. Sars, 1896) in Gutu & Sieg’s classification to just one (Leptognathia) in the Larsen & Wilson version. Very recently, Leptognathia itself has been partially revised, reduced in species complement, and split into three genera, Biarticulata, Forcipatia and Leptognathia sensu stricto, largely based on uropod morphology (Larsen & Shimomura 2007). Further restriction of the genus Leptognathia is highly probable, clustering around the type-species, L. breviremis (Lilljeborg, 1864).