Pseudotanais nipponicus, Mclelland, 2007

Mclelland, Jerry A., 2007, Family Pseudotanaidae Sieg, 1976 *, Zootaxa 1599, pp. 87-99 : 93-98

Pseudotanais nipponicus , n.sp.

Figures 4–6

Material examined. Holotype, non-ovigerous female, 2.2 mm (KMNH IvR 500.189), station XR-5, 42°23.83’N, 145°31.06’W, Kamchatka Trench , North Pacific, 16 September 2001, 3145–3265 metres . Paratypes: 1 female, 1.4 mm and 1 juvenile, 0.8 mm (KMNH IvR 500.190), from type locality; 1 female, 1.6 mm (dissected and slide mounted; KMNH IvR 500.191), station XR-7, 42°12.87’– 42°12.10’N 145°33.93’– 145°32.05’E, 3853–3858 metres, 17 September 2001.

Diagnosis. Pseudotanais with carpal blade-like setae on pereopods 2–6 (those on pereopods 2 and 3 greater than half as long as propodus), pereopods 2 and 3 having terminal spiniform setae of propodus subequal to length of dactylus plus unguis, pereopods 5 and 6 having superior carpal setae as long or longer than propodus, pereopod 1 distal superior setae of merus and carpus of unequal lengths, and antenna articles 2 and 3 having short, stout spiniform setae.

Etymology. The specific name refers to an alternate name for the island nation of Japan, adjacent to the type locality in the northern Pacific Ocean.

Description - based on non-ovigerous female holotype and dissected paratype. Body length 1.4–2.2 mm, Body ( Figs. 4A,B) 3.7 times as long as broad.

Cephalothorax shorter than pereonites 1–3, subtrapezoidal, narrowing anteriorly, about equal in width to pereon, with pair of antero-lateral setae, 16 % of total length; eyelobes absent.

Pereon 63.9 % of total length, pereonite 1 abbreviated. Pereonites 1 and 4–6 with pair of dorso-lateral setae, 2–6 with pair of minute antero-lateral setae, and 4–5 with additional pair of medio-lateral setae.

Pleon shorter than pereonites 5 and 6 combined, 18.7 % of total length. Pleonite 5 with pair of dorso-lateral and pair of medio-lateral setae.

Pleotelson subequal to pleonites 4–5, 6.9 % of total length, apex slightly produced, with pair of distolateral setae.

Antennule ( Fig. 4D) 22 % of body length, with three articles. First article 56.1 % of total length, 5.6 times as long as broad, with one long and five short medial simple setae, one short distal simple seta, two long unequal distal simple setae and two distal broom setae. Second article twice as long as broad, with one short and two long, unequal distal simple setae. Distal article 5.2 times as long as broad, terminating with two simple setae (one long, one short) and four bifid-tipped setae.

Antenna ( Fig. 4E) with six articles, 96.2 % length of antennule. Second article 1.1 times as long as broad, slightly shorter than third article, both articles distally with short, stout spiniform seta (larger on article 2). Fourth article 10.1 times as long as broad, with two long and one short distal simple setae, and three distal broom setae. Fifth article 4.3 times as long as broad, distally with one long simple seta. Sixth article small, terminating with four simple setae.

Mouthparts. Labrum not observed. Mandibles ( Figs. 5A,B) with distal margins denticulate (left) and crenulate (right), right lacinia mobilis represented by short, pointed process, left lacinia mobilis well developed and denticulate, pars molaris acuminate, with four to five small subdistal denticles. Labium not observed. Maxillule ( Fig. 5E) endite terminating with nine spiniform setae, three of which have a subterminal setule, and two accessory setae. Maxilla not observed. Maxilliped ( Fig. 5C) bases completely fused, with small seta near each palp location and two longer medially located setae; endites fused between one third and two thirds their length, each with one short seta and two short cusps, with lateral margins smooth; palp with four articles; article 1 without setae; article 2 with one inner-edge simple seta, two inner-edge spiniform setae, and one outer-edge simple seta; article 3 with three inner-edge spiniform setae and one inner-edge simple seta; article 4 with one small outer-edge simple seta, four inner-edge spiniform setae, and one inner-edge simple seta. Epignath not observed.

Cheliped ( Fig. 4C) strongly built, chela not forcipate; sclerite well developed. Basis twice as long as broad, with distal superior seta. Merus triangular, with inferior seta. Carpus 1.9 times as long as broad, with two unequal medial inferior setae, one distal superior seta and one proximal superior seta. Propodus 3.7 times as long as broad, about 1.8 times as long as carpus, palm with five short setulate comb setae. Fixed finger with one inferior seta, three superior setae and one seta near articulation with dactylus. Dactylus 61.3 % of propodus length, width narrower than fixed finger, with proximal spiniform seta.

Pereopod 1 ( Fig. 6A) coxa with seta. Basis 7.6 times as long as broad, with eight marginal setae (seven superior, one infero-proximal). Ischium with small seta. Merus 3.8 times as long as broad, distally with long superior seta. Carpus 2.5 times as long as broad, 1.4 times as long as merus, distally with one short superior seta and one long superior seta (about twice as long as that of merus). Propodus 7.6 times as long as broad, distally with short inferior seta. Dactylus without seta, length with unguis slightly longer than propodus.

Pereopod 2 ( Fig. 6B) coxa with seta. Basis 6.7 times as long as broad, with medial superior broom seta and eight marginal setae (six inferior, two superior). Ischium with short inferior seta. Merus 2.1 times as long as broad, distally with one short inferior simple seta and one short inferior spiniform seta. Carpus 3.2 times as long as broad, about 1.2 times as long as merus, distally with one short superior simple seta, one inferior blade-like seta of about 65 % length of propodus and one short spiniform seta with broad basal collar. Propodus 6.4 times as long as broad, with inferior and superior marginal spinules and one long distal inferior spiniform seta. Dactylus without setae, length with unguis slightly longer than half as long as propodus.

Pereopod 3 ( Fig. 6C) basis with five marginal setae (three inferior, one supero-proximal) and without broom seta. Ischium with short inferior spiniform seta. Carpus with inferior blade-like seta of about 80 % length of propodus and one short spiniform seta with broad basal collar (blade longer than that of pereopod 2). Propodus 5.6 times as long as broad. Dactylus bifid-tipped. Otherwise similar to pereopod 2.

Pereopod 4 ( Fig. 6D) coxa with seta. Basis 4.3 times as long as broad, with one medial broom seta and five marginal inferior setae. Ischium with one short setulose spiniform seta and one short simple seta. Merus 2.5 times as long as broad, distally with one short inferior spiniform seta and one short inferior simple seta. Carpus 3.5 times as long as broad, 1.9 times as long as merus, distally with one short superior simple seta, two unequal posterior spiniform setae, one inferior blade-like spiniform seta of about 35 % length of propodus and superior marginal spinules. Propodus five times as long as broad, slightly shorter than carpus, distally with one long supero-terminal spiniform seta with heavily setose distal half, one stout inferior spiniform seta, one short inferior simple seta, one superior broom seta and superior and inferior marginal spinules. Dactylus fused with unguis to form claw, margins slightly setulose, length with unguis less than half as long as propodus.

Pereopod 5 ( Fig. 6E) basis with three marginal inferior setae. Ischium with two unequal simple setae. Carpus distally with superior seta extending beyond propodus, stout serrate spiniform seta, and inferior blade-like seta of about 40 % of propodus length. Otherwise similar to pereopod 4.

Pereopod 6 ( Fig. 6F) basis with proximal simple seta and superior broom seta. Ischium with two unequal simple setae. Merus lacking distal simple seta. Carpus distally with superior seta subequal to length of propo- dus, inferior blade-like seta of about 45 % of propodus length, and stout serrate spiniform seta. Propodus with additional terminal spiniform seta and lacking broom setae. Otherwise similar to pereopod 4.

Pleopods ( Fig. 4F) rami elongate, with terminal setae only. Endopod about four fifth as long as exopod, with five terminal setae (innermost very short). Exopod with nine terminal setae.

Uropods ( Fig. 4G) exopod with two articles, slightly shorter than endopod, proximal article about half as long as ramus, with one distal simple seta, distal article with two unequal simple setae. Endopod with two articles, proximal article about half as long as ramus, with one long distal simple seta and two broom setae, distal article with four long and one short simple setae and two broom setae.

Remarks. Because of its acuminate pars molaris bearing subterminal denticles, this new species appears to belong to a subset of the “affinis group”, as defined by Bird & Holdich (1989), that also includes Pseudotanais longisetosus Sieg, 1977 ; P. longispinus Bird & Holdich, 1989 ; and P. nordenskioldi Sieg, 1977 . The new species appears nearly identical to P. longispinus except for minor differences in the setation of the pars molaris, the presence of dorsal and lateral setae on the thoracic and abdominal segments, and unequal merus and carpal superior setae on pereopod 1 (equal lengths in P. longispinus ). Furthermore, P. nipponicus has a cephalothorax which is considerably shorter in proportion to the length of pereonites 1–3 (cephalothorax is subequal to pereonites 1–3 in P. longispinus ) and has a peculiar spiniform seta with a short, round basal collar on the carpus of pereopods 2–3. Both species feature a pars molaris with subterminal teeth except that the new species apparently has less setation with only four to five small subterminal teeth whereas P. longispinus has “one long and about eight short terminal denticles” the longest of which is four times the length of the others and has secondary spinules. Additionally, the distal half of the long terminal setae on the propodus of pereopods 4–6 are heavily setulose in P. nipponicus and a few of the spiniform setae of the maxillule endite are equipped with a subterminal setule; both features were not mentioned by Bird & Holdich (1989) for P. longispinus . The setation of the pereopods is nearly identical in both species, differing from P. nordenskioldi by having a long superior seta on the carpus of pereopods 4–5. The two species appear to have identical maxillipeds which differ from that of P. longisetosus by having two small cusps on the endites.