Tanaella Norman and Stebbing 1886

Genus Tanaella Norman and Stebbing, 1886

Diagnosis, female (modifed from Norman and Stebbing, 1886; Hansen, 1913; Sieg, 1986). Antennule with four articles. Antenna with five articles and article 3 with or without fusion line. Mandible molars well developed, of intermediate width between those of Typhlotanais and Leptognathia; and always with ring of small apical spines. Pereopods 1–3 propodus longer than dactylus and unguis. Pereopods 4–6 propodus shorter than dactylus and unguis. Pleopods present or absent. Uropods stout and uniramous (although minute exopod process can be observed in some species), shaped as a pincer and consisting of one or two articles.

Diagnosis, male. In general as the female. Antennule stouter than in female, usually with four articles but sometimes with five (T. tuberculata). Fully functional mouthparts, almost identical to those of the females, present. Pleopods always present in males.

Distribution. Tanaella has so far been recorded from the North Atlantic, the Indian Ocean, off the tip of South America, in Antarctic waters, off California, and now the Gulf of Mexico. This cosmopolitan distribution is consistent with most other deep-sea tanaidacean genera. Bathymetric range 44–4800 m. It may not be completely correct to assign this genus as ‘deep sea’. The majority of the species are found in the deep sea, but several exceptions are found. Of these exceptions most are found in the Antarctic and one could argue for a case of isothermic submergence. However, one species, Tanaella propinquus, is described from a shallow warm-water habitat (California).

Remarks. Sieg (1986) claims that the number of terminal spiniform setae on the maxillule was a reliable genus character. However, Larsen and Wilson (1998) and Larsen (2001) showed that this character was ontogenetically dependent in Bathytanais and Paratanais. Also, Larsen (1999) found this character unreliable in Agathotanais, and the number of terminal spiniform setae on the maxillule was finally considered invalid as a diagnostic character by Larsen (2002).