Paragathotanais nanus Bird & Holdich, 1988

Bird, Graham J, 2010, Tanaidacea (Crustacea, Peracarida) of the North-east Atlantic: the Agathotanaidae of the AFEN, BIOFAR and BIOICE projects, with a description of a new species of Paragathotanais Lang, Zootaxa 2730, pp. 1-22 : 5

Paragathotanais nanus Bird & Holdich, 1988

Figs 2 A–D

Bird & Holdich (1988): 1612–1613, figs 2c, 10–11. Guerrero-Kommritz (2003): 3.

Larsen (2006): 108, 118.

Identification reference. Bird & Holdich (1988).

Distribution records from the AFEN, BIOFAR & BIOICE surveys. Recorded from four AFEN samples, from the Ymir Ridge, Wyville-Thomson Ridge, and North Rockall Trough, at depths 797–1886 m; four BIOFAR stations, from the Iceland-Faroe Rise and Iceland Basin, at depths 430–1038 m; 47 BIOICE stations, from the Denmark Strait, Iceland Basin, Irminger Basin, and Reykjanes Ridge, at depths 230–2082 m. The highest count was 145 specimens from BIOICE sample 2268, Irminger Basin, at 450 m.

Distribution elsewhere. From North Feni Ridge to the South Biscay Slope, 1160–2227 m ( Bird & Holdich 1988).

Remarks. With regard to pereonite shape ( Fig. 2 A), this new material of Paragathotanais nanus shows this character to be more variable than described and illustrated in Bird & Holdich (1988) and some individuals have distinct ‘shoulders’ or weak processes above the pereopod insertion ( Fig. 2 B). These are more similar to the more angular males in this respect and discrimination of P. n a n u s from the sympatric P. robustus is slightly more difficult. The body shape of the more angular individuals is actually very similar to that of P. s p i n o s u s from the Gulf of Mexico ( Larsen 2005) but no other difference in morphology between the angular and normal forms of P. n a n u s could be found (e.g. Figs 2 C–D). It is quite possible that these are a moult stage on the developmental path towards becoming a secondary male, with very early preparatory males having a very narrow pleon with barely-visible rudimentary pleopod ‘buds’.

This species has proved to be common and occasionally abundant in the Iceland-Irminger basins, where mean benthic temperatures are between 2–8o C (mode 4o C). The upper bathymetric limit of distribution records has been considerably raised, from 1160 m (see above) to 230 m.

Figures

FIGURE 2. Comparative habitus of Paragathotanais nanus and P. robustus of similar sizes: A, P. nanus, non-ovigerous female; B, P. nanus, angular form, possibly “ incipient male ”; C, P. robustus. pereopod- 1 propodus, dactylus and unguis: D, P. nanus; E, P. nanus angular form. Scale bar: 0.5 mm for A – C, 0.25 mm for D – E.