Neotanais oyashio, Bamber, 2007

Bamber, Roger N., 2007, Suborders Apseudomorpha Sieg, 1980 and Neotanaidomorpha Sieg, 1980 *, Zootaxa 1599, pp. 13-40 : 30-34

Neotanais oyashio n.sp.

Figures 10–12

Material examined. Holotype, female (KMNH IvR 500.158), station TD8, 39º15.54’– 39º17.01’N 144º45.37’– 144º42.46’E, 5762–5733 metres, 4 m ORE beam trawl, 29 September 2001. Allotype. 1 male (KMNH IvR 500.159), same locality . Paratypes: 1 female without cephalothorax (KMNH IvR 500.160), same locality .

Diagnosis. Typical smaller Neotanais , with cheliped dactylus shorter than fixed finger, cephalon about 1.5 times as long as wide, elongate 4th to 6th pereonites, ventral spurs on pleon keel and around 11 dorsal setae on cheliped carpus; pleotelson one-quarter length of whole pleon, 1.7 times as wide as long, uropods attached just anterior of midpoint. Pleopod basis with three dorsal and three ventral plumose setae, endopod proximal article with four ventral plumose setae.

Etymology. Named after the Oyashio Current which flows down to the north of Japan (noun in apposition).

Description of female.

Body ( Fig. 10B). Elongate, holotype 9.3 mm long (tip of rostrum to posterior of pleotelson), 8.2 times as long as wide, narrower posteriorly.

Cephalothorax. Sub-triangular, 1.46 times as long as wide, anterior margin with conspicuous rounded rostrum, with single mid-lateral and anterolateral setae on each side. Eyes and eyelobes absent.

Pereonites. Pereonite 1 shortest, one-third as long as cephalothorax, lateral margins uniformly convex. Pereonites 2, 3, 4 and 5 progressively slightly longer. Pereonite 5 longest and twice as long as pereonite 1, each expanded postero-laterally at attachment of coxae. Pereonite 6 as long as pereonite 2, expanded posterolaterally at attachment of coxae (all pereonites respectively 2.3, 1.3, 1.2, 1.1, 0.9 and 1.2 times as wide as long).

Pleon. Twice as long as pereonite 5, of five free subequal pleonites bearing pleopods. Pleonites dorsally convex, 3.5 times as wide as long, ventral keel with conspicuous posteriorly-directed spiniform apophyses (“spurs”).

Pleotelson. About 0.25 times as long as whole pleon, 1.7 times as wide as long, uropods attached just anterior of midpoint.

Antennule ( Fig. 10C). Proximal peduncle article elongate, 4.35 times as long as wide, dense field of fine setules on proximal inner margin. Fourth article just longer than third, and 1.25 times as long as flagellum.

Antenna ( Fig. 10D). Proximal peduncle article with inner field of fine setules. Fourth article just longer than fifth, sixth article half length of fourth.

Mouthparts not examined.

Cheliped ( Fig. 11A). Carpus twice as long as wide, with 11 simple setae along dorsal margin, and two midventral setae. Chela ( Fig. 11B) fingers longer than palm; cutting edge of fixed finger with central rounded apophysis and four flattened “teeth” proximal to this, distal claw rounded. Dactylus shorter than fixed finger, with no apophyses on cutting edge, distal claw more slender.

Pereopod 1 ( Fig. 11D). Basis with only two short dorsal setae and one mid-ventral plumose sensory seta. Carpus shorter than merus. Propodus with four slender ventral spines, single slender ventrodistal denticulate spine, four dorsodistal setae and adjacent short, hooked spine with rounded lateral denticles. Dactylus plus unguis 0.7 times as long as propodus.

Pereopods 2 and 3 ( Fig. 12 A, B). Generally similar to pereopod 1, but with basis proportionately shorter and carpus longer than merus.

Pereopods 4 and 5 ( Fig. 12 C, D). Similar to pereopods 2 and 3, but unguis proportionately longer and arising from crown of distal denticles on dactylus; no distal hooked spine on propodus.

Pereopod 6 ( Fig. 12E). As pereopods 4 and 5, but propodus dorso-distally with five short bidenticulate spines.

Pleopods ( Fig. 11E). All alike. Basis elongate, 1.6 times as long as wide, with three dorsal and three ventral plumose setae. Endopod shorter than exopod with proximal articulation bearing four ventral plumose setae.

Uropod ( Fig. 10B; 10E). Biramous. Basis naked; exopod 0.95 times as long as proximal endopod segments; endopod elongate, broken, with at least nine segments.

Distinctions of male. Larger than female, allotype ( Fig. 10A) length 11.5 mm.

Cheliped ( Fig. 11C) showing typical dimorphism, carpus slender but not S-shaped proximally, dorsal margin with ten setae including mid-dorsal tuft of three setae. Chela elongate, palm longer than fingers; fixed finger with irregular denticulation on cutting edge. Dactylus longer than fixed finger, cutting edge with large proximal and subdistal tooth-like apophyses.

Uropod exopod proportions as female, endopod of 12 segments, as long as pleon.

Remarks. The only described species of Neotanais with the cheliped dactylus shorter than the fixed finger, a cephalon about 1.5 times as long as wide, elongate 4th to 6th pereonites, ventral “spurs” on the pleon keel and around ten dorsal setae (nine) on the cheliped carpus is N. barfodei Wolff, 1956 , to which the present species keys out in the identification key of Larsen (1999). However, that species has a proportionately shorter pleotelson with uropod insertion posterior to the mid point (at 0.62 times as long as pleotelson), only two ven- tral pleopod basis setae, and only three setae on the proximal article of the pleopod endopod; N. barfodei is a much larger species at maturity (body length 16 mm). The male of N. barfodei has the proximal end of the cheliped carpus S-shaped.

Of the three species previously recorded from waters in the vicinity of Japan (see above), N. insignis is immediately distinguished from N. oyashio n.sp. by its having the uropod insertion at the posterior of the pleotelson; N. tuberculatus (at 22 mm body length a much larger species) has the uropod insertion posterior to the midpoint of the pleotelson, fewer proximal pleopod setae, pereonite 4 longer than wide, and the uropod exopod longer than the proximal endopod segment; N. wolffi also has the uropod insertion posterior to the midpoint of the pleotelson, the uropod exopod longer than the proximal endopod segment, the fourth antennule peduncle article shorter than the flagellum, and a rugose (as well as setulose) proximal antennal article.