Neotanais triqueturus Wi, Suh & Yu, 2015, n. sp.

Neotanais triqueturus n. sp.

Figs 1–3

Material examined. Holotype: female collected from the eastern central Pacific KODOS area (St.1 10°29.979’N, 131°55.590’W, 5180 m depth), dissected and mounted on six slides (MABIKCR00235165).

Diagnosis. Female. Pereonites posterolateral margins swollen. Pleonites lateral margins gradually tapered and with mid-ventral spurs. Pleotelson relatively long (length: width 1: 1.4). Antenna article 1 without ornamentation. Left mandible setal row with three setae. Cheliped carpus with ventral protrusion and nine dorsal setae and dactylus almost as long as fixed finger. Short seta on pereopods 1–3 propodi with dorsal processes. Uropod exopod almost equal to length of first endopodal segment.

Etymology. The specific name is derived from the Latin adjective triqueturus, referring to the triangular shaped lateral margin of pleonite.

Description. Female. Non-ovigerous. Body (Fig.1 A, B) length 8.4 mm, 8.3 times as long as wide. Cephalothorax slightly shorter than pereonites 1–2, sub-triangular, 1.6 times as long as wide, proximal margin with conspicuous rounded rostrum, proximolateral margin bearing one simple seta, and without kneels, distolateral margin with oblique furrow, and with one seta on each side; eye lobes absent.

Pereon (Fig. 1) each pereonite with fine setae on proximo- and distolateral margins. Pereonite 1 shortest, 0.4 times as long as cephalothorax. Pereonites 2–6 distally convex. Pereonites 1–2 bearing two proximolateral setae and two distolateral setae. Pereonites 3–6 bearing one proximolateral seta and two disto-lateral setae. Pereonites 4–5 slightly longer than wide. Pereonites 3–5 equal in length and almost equal to width. Pereonite 6 distinctly shorter than pereonites 3–5. Pereonites 1–6 proportional lengths 11.9: 16.7: 19.0: 19.0: 19.0: 14.4.

Pleon (Fig. 1 A, B) 2.6 times longer than pereonite 6, pleonites with two pairs of plumose setae on mid-lateral margin. Each pleonite bearing pleopods. Pleonites laterally tapered and with mid-ventral spurs (Fig. 1 B). Pleonite 1 longest, 1.2 times as long as pleonite 2, pleonites 2–5 subequal in length. Pleotelson (Fig. 1 A, C) 0.3 times as long as pleon, 1.4 times as wide as long, uropods attached to disto-lateral margin just anterior to mid length; starting from the uropod insertion, upper lateral margins each bearing one minute simple spinule, disto-lateral margins each bearing three minute spinules dorsally and one long spinule and one minute spinule ventrally; apex with split.

Antennule (Fig. 2 A) with seven articles, with proportional lengths 54.8: 17.4: 8.0: 11.3: 2.8: 2.6: 3.1. Article 1 elongate, 3.5 times as long as wide, with irregular row of fine spinules on proximal margin and a row of spinules along proximoventral margin, proximodorsal margin with two simple setae, mid-dorsal margin with one broom setae, distodorsal margin with five setae, and mid-distal margin with one broom seta and one simple seta. Article 2 with four simple setae and two broom setae on distal margin. Article 3 with two broom setae and one simple seta on mid-distal margin. Article 4 longer than article 3 and without seta. Articles 5 and 6 each with one thick, foursegmented aesthetasc and two and three simple setae, respectively (Fig. 2 A, B). Article 7 with four simple setae at distal margin.

Antenna (Fig. 2 C) shorter and slender than antennule, with nine articles of proportional lengths 14.7: 18.6: 8.3: 16.4: 18.6: 7.8: 6.1: 6.6: 2.9. Article 2 with long simple seta and minute seta. Article 3 with one simple seta. Article 4 with one seta. Article 5 as long as article 2, with one broom seta and four simple setae. Articles 6 without seta. Articles 7 and 8 each with two setae. Article 9 with three setae.

Mouthparts (Figs. 1 E–J, 2A–F). Labrum (Fig. 1 D) distal margin almost rectangular, disto-lateral margins ornamented with setules. Left mandible (Fig. 1 E) incisor blunt and proximal region tapered, with dentiform processes along ventral margin; lacinia mobilis broad, with four irregular teeth along distal margin and spiniform seta on proximal margin, setal row with two setulose setae; molar process broad, with rim of pointed teeth. Right mandible (Fig. 1 F) incisor broad and distal margin with rough protrusions; setal row with three spiniform setae: ventro-most seta naked and with small round protrusions on distal margin, middle and dorso-most setae bipinnate; molar process similar to that of left mandible. Labium (Fig. 1 G) distal lobe elongate, with fusion line, palp rounded, with two simple setae on distal margin and with rows of setules, mid lobe densely covered with fine setules. Maxillule (Fig. 1 H) dorsal endite with eleven spiniform setae on distal margin: ten spiniform setae each with three or four processes along mid region (arrowed in Fig 1 H), one seta short and naked, surface ornamented with patches of setules; ventral endite with one long unipinnate seta and three short bipinnate spiniform setae on distal margin, with patches of setules on surface. Maxilla (Fig. 1 I) ventral lobe of fixed endite with several setae, dorsal lobe of fixed endite with two trifurcated spiniform setae (Fig. 1 J) and seven bipinnate setae; ventral lobe of movable endite with six bipinnate setae, dorsal lobe of movable endite with three bipinnate setae. Maxilliped (Fig. 2 D) endite without ornamentation ventral and dorsal margins, distoventral margin with five short spinulose setae, ventral margin distal with two bipinnate spiniform setae, mid-distal margin with one bipinnate seta. Body and palp not examined. Epignath not figured.

Cheliped (Fig. 2 E) basis broad, slightly longer than wide. Ischium a narrow incomplete band, extending from distal margin of basis. Merus triangular, with one ventral simple seta. Carpus 1.3 times as long as basis, twice as long as wide, mid-ventral margin with protrusion (arrowed in Fig. 2 E), with two ventral setae unequal in length and nine dorsal setae unequal in length. Propodus 1.5 times as long as wide, 1.6 times as long as basis, 1.2 times as long as carpus, with one seta near insertion of dactylus. Chela 1.9 times as long as palm, fixed finger cutting edge with five rounded teeth and steeply descending from ventral-most one to disto-most one, inner first one largest, distal claw blunt, ventral margin with four simple setae each at proximal, mid, and distal margin, dorsal margin with two simple setae of equal length. Dactylus almost equal length to fixed finger, with simple seta on mid-lateral margin, distal claw larger than that of fixed finger.

Pereopod 1 (Fig. 3 A) coxa with one seta on dorsal margin. Basis with four minute simple setae. Ischium with two slender simple setae of unequal length. Merus with four simple setae on distal margin. Carpus shorter than merus, with four slender simple setae on dorsal margin and four bipinnate setae and one short spiniform seta on ventral margin. Propodus longer than carpus and as long as merus, with six bipinnate spiniform setae on ventral margin, short curved seta with seven ventral processes and dorsal small processes (Fig. 3 B), dactylus on distal margin. Dactylus with slender seta on proximal margin. Unguis half the length of dactylus. Dactylus and unguis combined slightly shorter than propodus.

Pereopod 2 (Fig. 3 C) similar to pereopod 1, but basis shorter than of pereopod 1, with four broom setae and one minute simple seta. Merus with two slender simple setae. Carpus slightly longer than merus, with five ventral setae, short seta, and five dorsal setae. Propodus as long as carpus, bearing six bipinnate setae and one simple seta on ventral margin, ten dorsal slender setae, and short curved seta with seven denticles and dorsal processes. Dactylus and unguis combined length 0.7 times as long as propodus. Unguis 0.3 times as long as dactylus.

Pereopod 3 (Fig. 3 D) similar to pereopod 2, but basis with one broom seta and one minute simple seta. Merus almost equal to carpus in length, with five dorsal setae. Propodus longer than carpus, with ten dorsal setae and seven ventral bipinnate setae. Dactylus and unguis combined 0.8 times as long as propodus. Unguis 1.4 times as long as dactylus. Dactylus and unguis combined 0.8 times as long as propodus.

Pereopod 4 (Fig. 3 E) basis with five broom setae, carpus bearing five ventral setae, five dorsal setae, and one minute mid-distal seta. Propodus bearing five ventral setae, five distal setae, and one dorsal seta. Dactylus surrounded with blunt spines around of unguis and one slender seta near insertion of unguis, and lateral margin ornamented with two rows of setules. Dactylus and unguis combined 1.5 times as long as propodus. Unguis with setules along mid-lateral margins (arrowed in Fig. 3 F). Unguis 0.7 times as long as dactylus.

Pereopod 5 (Fig. 3 G) basis bearing seven broom setae. Carpus with four ventral setae and five dorsal setae. Propodus with six setae on ventral margin. Dactylus and unguis combined equal to that of pereopod 4.

Pereopod 6 (Fig. 3 H) similar to pereopod 6, but basis with three broom setae. Carpus with four ventral setae and four dorsal setae. Propodus with three ventral setae, five distal setae, and eight blunt bipinnate setae on distal margin (Fig. 3 I). Dactylus and unguis 1.4 times long as propodus and shorter than that of pereopod 5. Unguis 0.6 times as long as dactylus.

Pleopod 1 to 5 (Fig. 3 J) basis 1.5 times longer than maximum width, with two dorsal plumose setae and two ventral plumose setae. Exopod two-articled, first article with three dorsal plumose setae; second article 2.7 times as long as first, with five dorsal plumose setae and five posterior plumose setae. Endopod much stouter than exopod, with six dorsal plumose setae, seven distal plumose setae, and three ventral plumose setae.

Uropod (Fig. 2 F) biramous, basis 0.6 times as long as pleotelson, 1.3 times longer than region from insertion portion of uropod to apex of pleotelson. Exopod with two articles, second article longer than first article, 1.3 times as long as first endopodal article, first article with small seta on distal corner, second article with two terminal setae. Endopod ten-articled, first article without ornamentation, second article with three broom setae, third article with small seta, fourth article two broom setae and one simple seta, fifth article with small seta, sixth article with two broom setae and one simple seta, seventh with one simple seta, eight article with two broom setae, one small and one long simple setae, ninth article with two simple setae, and tenth article with one broom seta and one simple seta.

Remarks. Neotanais triqueturus n. sp. females correspond closely to the ‘ pfaffi group’ (N. armiger Wolff, 1956; N. giganteus Hansen, 1913; N. pfaffi, Wolff, 1956; and N. pfaffioides Lang, 1968) described by Gardiner (1975), which is characterized by the pereonites having a swollen distolateral margin, pleonites with mid-ventral spurs, and pleonites with tapered lateral margins. But N. triqueturus can be differentiated from the ‘ pfaffi group’ by its larger ratio of length to width of the cephalothorax (1.6: 1), the cheliped showing the combination of the ventral process on the carpus and the large protrusion on the mid-dorsal region of the fixed finger (Table 1). The medially or distolaterally swollen margins of pereonites can also be characteristics of N. barfoedi Wolff, 1956, N. oyashio Bamber, 2007, N. tuberculatus Kudinova-Pasternak, 1970, and N. zenkevitchi Kudinova-Pasternak, 1973. They share some of the same characteristics, but can be differentiated by a comprehensive comparison between morphological characteristics, as shown in Table 1. N. triqueturus and N. zenkevitchi share some characteristics, including the tapered shape of the lateral margin of the pleonites, the cheliped having the ventral process on the carpus, a large protrusion on the mid-dorsal region of the fixed finger, and the cheliped dactylus bearing of equal length to the fixed finger; however, the two species can be differentiated by the ventral and dorsal setal number of the pleopod basis (2, 2 vs. 4, 2, respectively). In particular, the length of uropod is shorter than the pleon in N. oyashio and N. tuberculatus, while it is longer in N. triqueturus and N. zenkevitchi.