Metatanais Shiino, 1952

Blazewicz-Paszkowycz, Magdalena & Zemko, Karol, 2009, A new species of Metatanais Shiino, 1952 (Crustacea, Tanaidacea, Paratanaoidea) from Australian coral reefs, with a redefinition of the genus, ZooKeys 18 (18), pp. 129-141 : 131-132

Genus Metatanais Shiino, 1952

Metatanais Shiino, 1952: 23 .

Diagnosis: Body rigid, well calcified, cuticle surface smooth and glossy; eyes present, pigmented; all pereonites wider than long; pleon half as long as pereon. Antennule robust, 3- articled with article 1 large, embracing base of article 2; articles 2 and 3 as long as wide. Antenna robust, 6-articled; article 4 only little longer than article 2. Labrum hood-shaped, setose. Mandibles robust, lacinia mobilis of moderate size; molar with 5–6 tubercles. Maxillule with eight terminal spines and distally setose outer margin; palp with two distal setae. Maxilliped endites oval, plate-like, longer and wider than basis, with a few short setae terminally. Epignath with cluster of short setae distally. Cheliped compact, attached by sidepiece, merus and carpus without setae ventrally; fixed finger with minute seta ventrally and two minute setae on inner margin. Pereopods 1–6 ambulatory; pereopods 1–3 ischium lacking setae; pereopods 1–2 merus lacking setae; pereopods 3–6 merus with spines; pereopods 1–6 carpus with spines. Pleopods absent in females. Uropods uniramous; endopod biarticulated.

Type species: Metatanais cylindricus Shiino, 1952 ; by original designation; gender masculine.

Species included: M. cylindricus , M. bipunctatus sp. n.

Remarks

Metatanais has a well-calcified, smooth and glossy cuticle. The calcification is much strong- er than in most Pseudotanaidae ( Sieg 1976) or Nototanaidae ( Sieg 1976) , in which families the genus have been classified in the past, and can be only compared to some genera of the Agathotanaidae ( Lang 1971) and Colletteidae sensu lato ( Larsen and Wilson 2002) for example Libanius Lang, 1971 , although their cuticle is rather more matte in appearance.

Metatanais has a three-articulated antennule, with the first article robust and overlapping the small second article, a disc-shaped maxilliped endite, an epignath tipped by bunch of small setae, a lack of regular setae on the merus and carpus of all pereopods, and a uniramous uropod. Th is unique combination of characters was not used in the definition given by Shiino (1952), while the emphasis in his discussion was on ‘degenerated pleopods’ and for this reason an affinity of Metatanais with Pseudotanais Sars, 1882 was suggested.

In the first phylogenetic tree for the Tanaidomorpha ( Larsen and Wilson 2002), Metatanais was classified with the Nototanaidae sensu lato, owing to its three-articled antennule, and lack of plumose seta on pleonites (characteristic for the Paratanaidae Lang, 1949 ), its short uropod and lack of spines on second and third antenna articles (in contrast to the Leptognathiidae Sieg, 1976 ) and regularly developed pleonites (in contrast to the Pseudozeuxidae Sieg, 1982 ). Further attempts to understand the relationships within the Tanaidomorpha have demonstrated that the Nototanaidae is a polyphyletic family (Bird and Larsen in press., Błażewicz-Paszkowycz and Poore 2008) and none of the taxa formerly included show affinities to Metatanais ( Blazewicz-Paszkowycz and Poore 2008) . Alternatively, Bird and Larsen (in press) implied a weak relationship between Metatanais and the Paratanaidae . Th is uncertain position of Metatanais compels us to regard it as Nototanaidae sensu lato at present, until the whole suprageneric classification within the Paratanaoidea is resolved better.