Figs 1–5
Material examined. Holotype, adult male (total length, 13.8 mm, without antennae), MBM 240861, Okinawa Trough (27 ° 40.300´N; 126 ° 54.174´E), RY0231, depth 2115 m, bottom sandy mud, coll. Zhongli Sha, by Agassiz trawl, 23 April 2014.
Description. Body (Fig. 1 A–B) length 13.8 mm. Eyes rounded, large and protruding, 0.36 of lateral length of cephalothorax. Body long, slender, pereonite 1 fused with head; dorsal transverse ridge between cephalothorax and pereonite 1. Preocular spines absent; supraocular spines long, slender and directed anteriorly, unarmed, not covering the eyes in dorsal view, about 3.0 times as long as diameter of eye. Further dorsal spines are lacking. All pereonites unarmed, with rough cuticle. Pereonites 1–3 of about same length and width; pereonite 4 longest, slightly narrower than pereonites 1–3, of about the same width as pereonites 6–7; pereonite 5 slightly longer than pereonites 4 and 6–7. Tergites of pereonites 5–7 with concave posterior border into which the following segment fits when the animal bends dorsally.
All pleonites fused with pleotelson, unarmed. Pleotelson length about 0.25 times body length, width about 0.5 of total pleotelson length, partly with small scattered tubercles. Posterolateral pleotelsonic spines strong and straight, unarmed, at 0.62 of pleotelson length, about 0.6 times as long as caudal part of pleotelson. Pleotelson apex prominent, triangular and caudally rounded.
Antennula (Fig. 3 A): length 0.18 times body length, with 2 flagellar articles; peduncular article 1 broadest, 1.4 times longer than wide and shorter than second one, unarmed; article 2 longest, 1.2 times as long as article 1, unarmed; article 3 slightly shorter than article 2, unarmed; flagellar article 1 a very short ring with 1 lateral slender bristle; article 2 2.6 times as long as peduncular article 3, with 8 groups of 2 aesthetascs accompanied by several simple setae, apically 2 terminal simple setae and another 2 aesthetascs.
Antenna (Fig. 3 B): peduncle length 0.9 times body length; article 2 short, 0.3 length of article 3, with 2 parallel rows of short setae; articles 3 and 4 with 2 parallel rows of setae, arranged in groups of 1 long and 1 shorter setae; article 5 long and slender, with a row of short setae, arranged in groups of 1 long and 1 shorter setae; flagellum broken, article 1 with 2 parallel rows of short setae.
Mouthparts typical of the family (Fig. 2 A–C).
Maxilliped (Fig. 2 D) with a long oval-shaped epipod, strong endite and five-segmented palp. Epipodite covered with fine setae laterally and medially. Endite as long as epipodite, surpassing the middle of the second palp article, distal margin covered with fine setae and 7 robust setulate setae, distolaterally with 3 short plumose setae.
Palp article 1 shortest, length 0.7 times length of second article, with few short simple setae on ventral margin and ventrolateral surface; palpal article 2 with short simple setae on ventral margin and ventrolateral surface; article 3 longest, 1.9 times longer than article 2, with dense simple and pectinate setae on ventral margin and ventrolateral surface and 2 long pectinate setae dorsodistally; article 4 about 1.5 times as long as article 2, with dense simple and pectinate setae on ventral margin and ventrolateral surface and 4 long pectinate setae dorsodistally; article 5 1.4 times longer than article 1, with long simple and pectinate setae apically.
Pereopod 1 (Fig. 3 C) more robust than pereopods 2–7; basis longer than propodus, 2.1 times longer than wide, distoventrally with several long and slender simple setae, dorsal surface equipped with row of setules; ischium 0.9 times basis length, 1.7 times longer than wide, ventrally with dense long simple setae on distal half; merus 0.5 times ischium length, 1.8 times wider than long, with dense long simple setae ventrally and 2 anterodistal setae, carpus trapezoidal, 1.6 times wider than long, about as long as merus, with dense long simple setae ventrally; propodus subchelate and slender, 2.2 times carpus length, twice as long as wide; ventrally and partly laterally with dense long slender simple setae, dorsolateral surface with dense pectinate setae; dactylus shorter than propodus, 3.3 times longer than wide, with a unguis and a secondary unguis, and between bearing a seta, with several long and slender simple setae.
Pereopods 2–4 similar, with long setae on posteromedial margins, without spines on anterolateral margins; long filter setae present on ischium, merus, carpus and propodus but lacking on dactylus (unknown in pereopod 3). Pereopod 2 (Fig. 3 D) basis 1.8 times longer than wide, dorsally unarmed, distoventrally with several long and slender simple setae; ischium length 0.7 times basis length, 1.4 times longer than wide, dorsally unarmed, ventrally with 2 parallel rows of setae, every row with 6 groups of setae and arranged in groups of 1 long filtering seta and 1 shorter simple seta; merus 1.5 times ischium length, 1.8 times longer than wide, with 1 small simple seta distodorsally, ventrally with 2 parallel rows of setae, every row with 6 groups of setae and arranged in groups of 1 long filtering seta and 1 shorter simple seta; carpus 2.2 times merus length, 6.8 times longer than wide, with several small simple setae dorsally, ventrally with 2 parallel rows of setae, every row with 16 groups of setae and arranged in groups of 1 long filtering seta and 1 shorter simple seta; propodus almost as long as carpus, 9.8 times longer than wide, with 2 moderate setae and 3 small simple setae dorsally, ventrally with 2 parallel rows of setae, every row with 14 groups of setae and arranged in groups of 1 long filtering seta and 1 shorter simple seta; dactylus 0.5 times propodus length, 11.1 times longer than wide, with 4 small simple setae dorsally, 2 small simple setae ventrally; unguis 0.5 times dactylus length, with a short ventral claw and a medial seta.
Pereopod 3 (Fig. 4 A) basis 2.8 times longer than wide, dorsally unarmed, distoventrally with several long and slender simple setae; ischium 0.6 times basis length, 1.6 times longer than wide, dorsally unarmed, ventrally with 2 parallel rows of setae, every row with 7 groups setae and arranged in groups of 1 long filtering and 1 shorter simple seta; merus 1.5 times ischium length, 2.1 times longer than wide, dorsally unarmed, ventrally with 2 parallel rows of setae, every row with 7 groups setae and arranged in groups of 1 long filtering and 1 shorter simple seta; carpus 2.3 times merus length, 6.5 times longer than wide, with several small simple setae dorsally, ventrally with 2 parallel rows of setae, every row with 15 groups of setae and arranged in groups of 1 long filtering and 1 shorter simple seta; propodus broken off.
Pereopod 4 (Fig. 4 B) basis 3.6 times longer than wide, dorsal margin with a big triangular tooth and scattered with several small tubercles, distoventrally with several long and slender simple setae; ischium 0.6 times basis length, 2.6 times longer than wide, dorsally unarmed, ventrally with 2 parallel rows of setae, every row with 7 groups of setae and arranged in groups of 1 long filtering and 1 shorter simple seta; merus almost as long as ischium, 2.3 times longer than wide; with 1 small simple seta distodorsally, ventrally with 2 parallel rows of setae, every row with 7 groups of setae and arranged in groups of 1 long filtering and 1 shorter simple seta; carpus 2.0 times merus length, 5.0 times longer than wide, with several small simple setae dorsally, ventrally with 2 parallel rows of setae, every row with 12 groups of setae and arranged in groups of 1 long filtering and 1 shorter simple seta; propodus about 0.9 times carpus length, 7.8 times longer than wide, with 2 moderate setae and 3 small simple setae dorsally, ventrally with 2 parallel rows of setae, every row with 11 groups of setae and arranged in groups of 1 long filtering and 1 shorter simple seta; dactylus 0.6 times propodus length, 10.0 times longer than wide, with 4 small simple setae dorsally and ventrally; unguis 1 / 3 times dactylus length, with a short ventral claw and a medial seta.
Pereopod 5 (Fig. 4 C) broken off, only basis remains, 3.4 times longer than wide, with 3 feather-like setae dorsally, dorsal and ventral surface covered with extremely dense mat of fine setae.
Pereopods 6–7 (Figs. 4 D–E) shorter and stronger than pereopods 2–4; two distal claws, stouter and much shorter than unguis of pereopods 2, 4. Pereopod 6 (Fig. 4 D) basis longest article, 3.7 times longer than wide, with 3 feather-like setae dorsally, dorsal and ventral surface covered with extremely dense mat of fine setae; ischium 0.6 times basis length, 2.3 times longer than wide, with few simple setae ventrally, dorsal and ventral surface covered with extremely dense mat of fine setae; merus 0.6 times ischium length, 1.4 times longer than wide, dorsal and ventral surface covered with extremely dense mat of fine setae, ventral surface with 2 row of short spines, each row arranged in 4 spines; carpus 0.9 times length merus, 0.8 times longer than wide, dorsal and ventral surface covered with few setules, ventral surface with 2 row of short spines, each row arranged in 4 spines; propodus 2.6 times longer than carpus, 3.3 times longer than wide, dorsal surface covered with few fine setae, ventral surface with 1 row of 7 short spines; dactylus 0.9 times propodus length, 5.0 times longer than wide, with few simple setae and several setules dorsally and ventrally; one simple seta and unguis, secondary unguis distally.
Pereopod 7 (Fig. 4 E) basis longest article, 2.8 times longer than wide, with 3 feather-like setae dorsally, dorsal and ventral surface covered with extremely dense mat of fine setae; ischium 0.6 times basis length, 1.6 times longer than wide, with few simple setae ventrally, dorsal and ventral surface covered with extremely dense mat of setules; merus 0.8 times ischium length, 0.6 times longer than wide, dorsal and ventral surface covered with extremely dense mat of fine setae, ventral surface with 2 row of short spines, each row arranged in 4 spines; carpus 0.9 times longer than merus, 1.6 times longer than wide, dorsal and ventral surface covered with extremely dense mat of fine setae, ventral surface with 2 row of short spines, each row arranged in 4 spines; propodus 2.7 times longer than carpus, 3.6 times longer than wide, dorsal surface covered with few setules, ventral surface with 1 row of 6 short spines; dactylus 0.8 times propodus length, 4.7 times longer than wide, with few simple setae and several setules dorsally and ventrally, one simple seta and unguis, secondary unguis distally.
Penial plate elongate (Fig. 5 B), tapering proximally and distally, unarmed.
Pleopod 1 (Fig. 5 C) peduncle with 11 small triangular spine-like robust setae in a row laterally, ventromedially with seven coupling setae with hooked tips; exopod 1.1 times longer than endopod, 3.4 times as long as wide, laterally and apically with long plumose setae, posterior surface with transverse groove, ending with a protrusion on distal half of lateral margin; endopod with long plumose setae laterally and apically.
Pleopod 2 (Fig. 5 D) exopod about as long as endopod, with long plumose setae laterally and apically; endopod of about same width as exopod, with long plumose setae laterally and apically; stiletto-like appendix masculina 1.1 times as long as endopod, with acute apex.
Pleopod 3 (Fig. 5 E) exopod 1.2 times longer than endopod, setae absent; endopod of about same width as exopod, with a long and slender setae distolaterally.
Pleopod 4 (Fig. 5 F) exopod 1.1 times longer than endopod, setae absent; endopod of about same width as exopod, with few simple setae laterally and 4 long and slender setae distolaterally.
Pleopod 5 (Fig. 5 G) exopod 1.1 times longer than endopod, setae absent; endopod of about same width as exopod, with few simple setae laterally and 4 long and slender plumose setae distolaterally.
Uropod (Fig. 5 A) biramous, peduncle with 14 long plumose setae on distolateral margin and a small triangular spine distally, surface laterally unarmed; exopod broader than linear endopod, about 1.3 times as long as endopod, unarmed distally; endopod with 3 simple setae distally.
Etymology. The species name is derived from the oceanographic vessel “ Kexue” of Institute of Oceanology, Chinese Academy of Sciences, which contributed substantially to biological studies of Okinawa Trough.
Distribution and habitat. Only known from type locality (Okinawa Trough, East China Sea, 2115 m).
Remarks. The present new species is assigned to Litarcturus because of the following characters: with the tendency to reduce cuticular spines on the whole body surface; cephalothorax with one pair of supraocular spines, in some cases reduced or very small; caudal pleotelsonic spines comparatively short.
Litarcturus kexueiae sp. nov. belongs to the third group with L. granulosus (Nordenstam, 1933) and L. stebbingi (Beddard, 1886), with supraocular and caudal pleotelsonic spines. However, L. kexueiae sp. nov. differs markedly from L. granulosus as its supraocular spines are longer than the cephalothorax apex (versus supraocular spines not longer than the cephalothorax apex), and from L. stebbingi as its caudal pleotelsonic spines are longer than the pleotelson apex (versus caudal pleotelsonic spines not longer than the pleotelson apex).