(Figs. 1–4)
Material examined. Holotype: female, Specimen No. MBM 240860. CL 8.2 mm, TL 30.4 mm, Yap Seamount, ROV "FAXIAN" station FX-DIVE 19 (137 º 47 'E, 8 º 51 'N), 255m, 22 December 2014, collected by Jiang Wei.
Description. Rostrum (Figs. 1, 2 a) slender, tapering, about 1.4 times as long as carapace, strongly upturned; dorsal margin armed with 6 widely spaced teeth, of them anterior 4 small and posterior 2 distinctly larger than anterior tooth; posteriormost tooth located slightly posterior to orbital margin, with 4 short setae anterior to its base; apex bifid; ventral margin with 8 teeth increasing in size and becoming more erect proximally.
Carapace (Fig. 1) laterally compressed, smooth, less than 1.5 as long as broad. Epigastric prominent, subequal in size to posterior teeth of dorsal rostral series, locate slightly posterior to midlength of carapace. Suborbital angle produced forwards, forming a long, acute tooth. Antennal spine strong, approximate to and exceeding as far as suborbital angle. Branchiostegal spine submarginal, far distant from anterolateral margin of carapace (rather hepatic in position), smaller than antennal spine. Round pterygostomial angle present.
Abdominal somites (Figs. 1, 2 j, k, l) generally smooth, third somite strongly produced posteriorly into a bluntly triangular cap overhanging fourth tergite; fifth pleuron rounded posteroventrally; sixth somite elongate, about twice as long as fifth somite. Uropods (Fig. 2 m) slightly shorter than telson. Exopod as long as endopod; outer margin nearly straight, ending in a small acute tooth, accompanied with a longer movable spine medially. Telson (Fig. 2 m, n) slender, tapering, distinctly longer than sixth pleomere; posterior margin with produced, triangular without narrow endpiece, bearing 2 pairs of movable spines (mesial pair larger); lateral margin each bearing 2 movable spines, anterior pair larger.
Eyes (Figs. 1, 2 a) moderately large; eyestalk slender; cornea subglobular, shorter than eyestalk.
Antennular peduncle (Fig. 2 a) slender, reaching midlength of antennal scale, basal segment longest; second segment shortest, about 1 / 3 length of third segment, latter less than half length of basal segment, distal two segments combined shorter than basal segment. Stylocerite broad in basal portion but abruptly narrowing near tip, overreaching middle of second segment of antennular peduncle, terminating acutely.
Antennal scale (Fig. 2 a) relatively broad, 5.7 times as long as wide at tip; anterior margin of lamella convex, far exceeding antennular peduncle; outer margin slightly concave and terminating into a strong lateral spine not reaching distal margin of lamella. Basicerite with moderately small distolateral ventral spine; carpocerite stout, cylindrical, reaching level of distal end of basal segment of antennular peduncle.
Mandible (fig. 3 c) without palp, molar process bearing four strong irregular teeth, incisor process rather broad and with three sub-acute teeth. Endite of maxilla (Fig. 3 d) with long setae; palp well developed, not tapering, nonsetose; scaphognathite rather narrow, marginally fringed with setae. First maxilliped (Fig. 3 e) with distal endite broad, mesial margin bearing numerous spiniform setae; palp well developed, tapering, non-setose; distal part of exopod five-articulated, tip bearing setae; caridean lobe of exopod broad, rounded, outer margin fringed with setae. Second maxilliped (Fig. 3 f) endopod with ischium and merus; carpus short; propod rounded, long, stout, spine-like setae on outer margin; dactyl with, stout, spine-like setae on inner margin; elongate exopod, distal part six segmented, lateral margin bearing short setae. Third maxilliped (Fig. 3 g) slender; ultimate segment tapering, tip and both lateral margin bearing short setae; penultimate segment 0.8 length of ultimate segment, smooth, nonsetose; antepenultimate segment stouter than distal two segments, less than three times as long as penultimate segment; exopod short, not tapered, reaching 1 / 3 length of antepenultimate segment.
First pereiopod (Figs. 2 b, c)slender, fingers about 2 / 3 length of palm, distally setose; palm glabrous. Carpus subcylindrical, about 2.7 times as long as palm. Merus sub-equal in length to carpus, unarmed. Ischium much stouter, about 1 / 3 length of merus.
Second pereiopods (Figs. 2 d, e, 3 a, b) subequal and similar from right to left, overreaching distal margin of antennal scale by length of chela; cutting edge of dactylus and pollex with 3 and 2 small obtuse teeth, respectively; chela more than twice as long as chela of first pereiopod. Fingers short, 1 / 3 length of palm, distally slightly hooked, setose, tips crossing when closed. Carpus subcylindrical, slightly widened distally, sub-equal in length to palm. Merus slender, cylindrical, nearly 1.5 times as long as carpus. Ischium slender, slightly shorter than merus.
Posterior three pereiopods (Figs. 2 f–i) slender, similar in structure. Dactyli tapering, distal parts strongly curved, about 1 / 8 length of propodi. Propodi generally smooth, ventral margin without spines, dorsal-distal margin bearing some setae. Carpi also smooth and unarmed, about half-length of propodi, distodorsal margin somewhat protruded into an obtuse process. Meri unarmed and slightly longer than propodi.
Pleopods without distinctive feature. Endopod of first pleopod short, narrow, with fine setae along outer margin, 1 / 3 length of exopod. Appendix interna of second pleopod (Fig. 3 h) long, tip overreaching middle of endopod.
Coloration. Body (Fig. 4) generally transparent and sparsely scattered with minute red dots; carpocerite of antennal peduncle, third maxilliped, basal segments of pereiopods and chelae of first pereiopods with tinge of pale red. Eye stalks pale yellow.
Etymology. The species is named in honor of the late Professor Ruiyu Liu (J. Y. Liu), the Institute of Oceanology, Chinese Academy of Sciences, for his great contribution to the carcinology of China.
Distribution. Presently only known from the Yap Seamount in the Western Pacific, at a depth of 255 meters.
Remakes. The new species is referred to Urocaridella because of the characteristic shape and arrangement of the rostral teeth, particularly the crest like basal dorsal rostral teeth, and the presence of branchiosteghal spine which lacking suture and situated far behind the anterior margin of the carapace.
Urocaridella liui sp. nov. is unique in this genus for many characters: This new species is from deep waters and with an almost colorless body. All other known species and undescribed species of the genus are from shallow waters less than 130 m deep and most if not all with striking coloration (see Chace & Bruce 1993; Debelius 1999; Minemizu 2000; Kawamoto & Okuno 2009; Humann & De Loach 2010; Minemizu 2013). Morphologically, U. liui sp. nov. is also very distinct in having a large overhanging triangular cap on the third abdominal somite and a much longer palm than fingers in the second pereiopod. Moreover, the fingers of the first pereiopods and the dactyli of the posterior pereiopods are also relatively shorter in U. liui sp. nov. than the other species of the genus. The ventral margins of the propodi of the posterior pereiopods are smooth in U. liui sp. nov. but bearing spines at least in U. urocaridella, U. antonbruunii and U. vestigialis (not mentiond in the original description of U. pulchella). In addition to the characters mentioned above, the ambulatory legs (third to fifth pereopods) are much more stout in the new species compared to the other congeneric species.