Neotanais kuroshio, Bamber, 2007

Bamber, Roger N., 2007, Suborders Apseudomorpha Sieg, 1980 and Neotanaidomorpha Sieg, 1980 *, Zootaxa 1599, pp. 13-40 : 35-39

Neotanais kuroshio n.sp.

Figures 13–15

Material examined. Holotype, large female (KMNH IvR 500.161), station TD8, 39º15.54’– 39º17.01’N 144º45.37’– 144º42.46’E, 5762–5733 metres, 4 m ORE beam trawl, 29 September 2001. Paratypes: 1 smaller female, paratype, 2 damaged females (KMNH IvR 500.162), same locality.

Diagnosis. Typical larger Neotanais , with only five dorsal setae on the cheliped carpus, cheliped dactylus longer than the fixed finger, and uropod exopod only half length of the proximal endopod segment; no spurs on ventral keel of pleon; pleotelson 1.8 times as wide as long, uropods attached posterior of midpoint; pleopod basis with two dorsal and one ventral plumose setae, endopod proximal article with four ventral plumose setae.

Etymology. Named after the Kuroshio Current, which flows from the south up the western side of Japan (noun in apposition).

Description of female.

Body ( Fig. 13A). Elongate, holotype 22 mm long (tip of rostrum to posterior of pleotelson), 7.8 times as long as wide.

Cephalothorax. Sub-triangular, 1.2 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, 0.4 times as long as cephalothorax, lateral margins uniformly convex. Pereonites 2 to 6 subequal. Pereonite 4 longest and 1.5 times as long as pereonite 1. Pereonites 2 and 3 slightly expanded postero-laterally at attachment of coxae (all pereonites respectively 2.2, 1.5, 1.4, 1.3, 1.4 and 1.6 times as wide as long).

Pleon. 2.2 times as long as pereonite 4, of five free subequal pleonites bearing pleopods. Pleonites dorsally convex, five times as wide as long, ventral keel without apophyses (“spurs”) ( Fig. 13B).

Pleotelson. 0.3 times as long as whole pleon, 1.8 times as wide as long, uropods attached posterior of midpoint (at 0.61 as long as pleotelson).

Antennule ( Fig. 13C). Proximal peduncle article elongate, 5.4 times as long as wide, with fine setules on proximal inner margin. Fourth article longer than third, and twice as long as flagellum.

Antenna ( Fig. 13D). Proximal peduncle article with rugosity on inner face. Fourth and fifth articles subequal, sixth article 0.7 times as long as fourth.

Mouthparts. Labrum not seen. Left mandible ( Fig. 14A) with blunt, simple pars molaris; pars incisiva with five rounded denticulations, lacinia mobilis a thin plate wider distally and exceeding tip of pars incisiva; setal row of two stout finely-setulose setae. Right mandible ( Fig. 14B) without lacinia mobilis, pars incisiva with thin, straight cutting edge, setal row with two stout finely-setulose setae and wider plate-like distal spine. Labium ( Fig. 14C) typical of the genus, palps with two distal spines on rounded papillae. Maxillule ( Fig. 14D) margins naked, outer endite with nine distal spines, inner endite with one long and four shorter setulose distal setae. Maxilla ( Fig. 14E) with simple setae on lobes of moveable endite, outer lobe of fixed endite with three bifurcate, one pinnate and three simple distal spines and inner subdistal seta, rostral row of inner lobe with eleven curved setae. Maxilliped ( Fig. 14F) basis and proximal palp article naked; second palp article with simple outer distal setae, three finely-setulose inner marginal setae and single simple sub-marginal seta; third article with six marginal and one sub-marginal simple setae, fourth article with simple subdistal and distal setae dorsally, three ventrodistal simple setae, and five stouter finely-setulose setae. Endite with finely setulose outer margin, distally with three inner pinnate spines, two adjacent simple spines and outer setulose seta. Epignath ( Fig. 14G) of two articles, marginally setulose, distally with about twenty fine setae.

Cheliped ( Fig. 13G). Carpus twice as long as wide, with five simple setae along dorsal margin, and two mid-ventral setae. Chela fingers shorter than palm; cutting edge of fixed finger with five rounded “teeth”, distal claw blunt. Dactylus longer than fixed finger, with no apophyses on cutting edge, distal claw slender.

Pereopod 1 (15A). Basis naked. Merus 1.24 times as long as carpus. Propodus with nine slender bidenticulate ventral spines, eight dorsal setae in distal half. Dactylus with slender unguis half length of propodus.

Pereopod 2 ( Fig. 13E). Basis almost naked, with one proximo-dorsal plumose sensory seta. Carpus longer than merus. Propodus with eight slender ventral setae, single slender ventrodistal denticulate spine, six dorsal marginal setae in the distal half, eight dorsodistal setae and adjacent short, hooked spine with lateral denticles. Dactylus plus unguis 0.8 times as long as propodus.

Pereopod 3 ( Fig. 15B). Similar to pereopod 2 but with only one subdistal dorsal propodal seta.

Pereopods 4 to 6 ( Fig. 15 C to E). Similar to pereopod 3 but with fewer propodal setae, unguis proportionately longer and arising from crown of distal denticles on dactylus; no distal hooked spine on propodus.

Pleopods ( Fig. 13F). All alike. Basis compact, 1.45 times as long as wide, with two dorsal and one small ventral plumose setae. Endopod shorter than exopod with proximal articulation bearing four ventral plumose setae.

Uropod ( Fig. 13H). Biramous. Basis naked. Exopod 0.5 times as long as proximal endopod segments. Endopod 0.9 times as long as pleon, with nine segments.

Male unknown.

Remarks. With only five dorsal setae on the cheliped carpus (four in the undamaged paratype), a cheliped dactylus longer than the fixed finger, and a uropod exopod only half the length of the proximal endopod segment, Neotanais kuroshio n.sp. is closest to N. peculiaris Lang, 1968 , N. giganteus Hansen, 1913 and possibly N. hessleri Gardiner, 1975 , although this last is known only from a manca, so is difficult to interpret. Both of the first two species have a more elongate cephalothorax and ventral pleon spurs; N. peculiaris has a proportionately longer 6th pereonite and pleotelson, with a more anterior uropod insertion on the pleotelson, only two pleopod endopod article 1 setae, and a characteristic flange on the proximal article of the antenna; N. giganteus has six setae on article 1 of the pleopod endopod and an antennular flagellum only one-quarter as long as the distal peduncle article. N. hessleri (from 5340 metres in the south Pacific) has a proportionately longer pleotelson (1.3 times as wide as long) and a uropod exopod only 0.3 times as long as the proximal endopod segment.

Of the three species previously recorded from waters in the vicinity of Japan, the characteristic distinction of N. insignis is as described above, N tuberculatus has ventral pleon spurs, and N. wolfii has a uropod exopod exceeding the length of the proximal endopod segment, inter alia. The key of Larsen (1999) would identify the present species as N. vemae Gardiner, 1975 , but that species also has a uropod exopod exceeding the length of the proximal endopod segment and far fewer setae on the proximal pleopod articles. N. kuroshio is distinct from the sympatric N. oyoshio (see above) in having no ventral apophyses on the pleonites, fewer dorsal setae on the cheliped carpus, the cheliped dactylus longer than the fixed finger, and the fourth antennule article twice as long as the flagellum, inter alia.

The variation between the large holotype female and the smaller paratype female (body length 6.5 mm) is informative. The characters of the trunk, pleotelson, uropod and pleopods are consistent, as are most of those of the cheliped, although the larger specimen has five dorsal carpal setae (four in the paratype). In the smaller paratype, the fourth antennal article is conspicuously shorter than the fifth, the proximal antennule peduncle article is less slender (4.6 times as long as wide), the fourth peduncle article is the same length as the third, and only 1.3 times as long as the flagellum, these antennular characters having been used by Gardiner (1975) as valuable for specific distinction within the genus.