Tanais Latreille, 1831 (partim.): G.O. Sars, 1877: 347, 370; G.O. Sars, 1882: 50; G.O. Sars, 1896: 33; Sieg, 1980: 11 –12.
Cryptocope G.O. Sars, 1882 (partim.): G.O. Sars, 1882: 50 –51; G.O. Sars, 1885: 74 –78; Forsstrand, 1886: 47; Norman, 1899: 340; Zirwas, 1911: 105; Hansen, 1913: 106, 109– 110, pl X; Nierstrasz, 1913: 33; Lang, 1949: 6, 8; Stephensen, 1932: 349; Lang, 1971 b: 403.
Leptognathia G.O. Sars, 1882 (partim.): Kudinova-Pasternak, 1965: 75, 88– 91; Belyaev, 1966: 88; Kudinova-Pasternak, 1968: 73; Lang, 1968: 160 –161; Lang, 1971 a: 361 –362; Gardiner, 1975: 225; Lang, 1972: 229 –235; Kudinova- Pasternak, 1981: 115; Sieg, 1983: 317.
Strongylura G.O. Sars, 1882 (partim.): Norman & Stebbing, 1886: 110, 133.
Paranarthrurella Lang, 197 a 1: Lang, 1971 a: 361, 363, 367; Sieg, 1973: 34 –281; Sieg, 1976: 178; Sieg, 1978: 121.
Robustognathia: Kudinova-Pasternak, 1989: 68, 33– 34.
Biarticulata Larsen & Shimomura, 2007 (partim): Larsen & Shimomura, 2007: 19; Bird, 2007: 75.
Gender: Feminine.
Type species: Leptognathia caudata Kudinova-Pasternak, 1965; by original designation ( Lang, 1971 a). Species included: Paranarthrurella caudata; P. ( = Leptognathia) dissimilis Lang, 1972; P. ( = Tanais) voeringi G.O. Sa r s, 1877.
Amended diagnosis: Female: antennule with five articles, distal article vestigial. Antenna with six articles. Labrum long and narrow. Mandibular molar rounded distally, with 5–7 short, flat distal setae, incisor large and gently rounded, lacinia mobilis large and widely separated from incisor. Maxillule with eleven spiniform setae distally and numerous simple setae on outer margin; labium strongly setose with poorly-developed outer lobe; maxilliped with narrow endites, bases with small seta distally; endites with pair of simple and pair of short flat setae distally. Epignath distally narrow. Chelipeds usually robust; attached to cephalothorax by sclerite; chela with well calcified ‘crushing margins’. All pereopods of walking type; pereopod- 1 setation strongly reduced; pereopods 2–6 with short and robust setae. Pleopods absent or reduced in female. Uropods biramous, both rami 2 -articled.
Male: swimming type; antennule with seven articles; articles 4–6 with numerous aesthetascs; mouthparts reduced; cheliped and pereopods similar to female; pleopod rami elongated with setulated setae distally; uropod endopod with three, exopod with two articles.
Remarks: The genus Paranarthrurella has a set of very distinctive characters, especially in the morphology of the mouthparts, which exclude it from any of the families recognized by Larsen and Wilson ( 2002). The systematic position of Paranarthrurella remains unresolved, and it is proposed that the genus becomes family incertae sedis until there is a better understanding of the systematics of the paratanaoid tanaidomorph genera.
Paranarthrurella is most closely related to Armatognathia Kudinova-Pasternak, 1987, sharing with it the specific mouthpart morphology which includes an elongated labrum (e.g. Fig. 2 C), a setose outer margin of the maxillule ( Fig. 2 F), and the bizarre shape of the mandibles ( Fig. 2 D). The mandible incisor is massive and gently rounded; the lacinia mobilis (on the left mandible only) forms a gentle depression that, together with the incisor, forms a spoon-like structure; the mandibular molar in both genera is large, but gently rounded distally, with short simple or blunt spiniform setae. The maxillipeds have quite narrow endites which are of similar width proximally and distally. A peculiar character in the genus is the projection on the inner margin of the cheliped dactylus, that matches a depression on the inner margin of the fixed finger (e.g. Fig. 3 A). It is difficult to judge the function of the structure without direction observation or at least information about stomach contents. It can be assumed however, that it is used for crushing the food particles (e.g. forminiferan tests).
Females studied by us have an antennule of five articles, although the last article is vestigial. This character has often been overlooked in the past, and is so far confirmed for such genera as Collettea Lang, 1973, Robustochelia Kudinova-Pasternak, 1983 and Tanaopsis G.O. Sars, 1896.
The family classification of Paranarthrurella remains uncertain, although it cannot be classified to either the Anarthruridae or the Agathotanaidae. The regular structure of uropods and cheliped attachment to the cephalothorax by a sclerite suggest its relationship to some leptognathids or colletteids. More probable however is that this genus, together with Armatognathia, constitute a new family that may yet be confirmed through phylogenetic analysis.