﻿A new ghost shrimp of the genus Pugnatrypaea (Decapoda, Axiidea, Callianassidae) from the South China Sea

﻿Abstract A new species of the genus Pugnatrypaea Poore, Dworschak, Robles, Mantelatto & Felder, 2019, Pugnatrypaearuiyuisp. nov., collected from the northern South China Sea, is described and illustrated. It is distinguishable from P.pugnatrix (de Man, 1905), P.iranica (Sepahvand, Momtazi & Tudge, 2015), and P.emanata Felder & Robles, 2020 in having the lower margin of the male major cheliped merus lacking a proximal hook. It is distinguishable from P.intermedia (de Man, 1905) and P.lobetobensis (de Man, 1905) in having the upper margins of both cheliped meri unarmed. A key to all species of Pugnatrypaea is provided.


Introduction
While working on a taxonomic study of the axiidean fauna (Crustacea, Decapoda) of the China seas, an undescribed species assignable to the genus Pugnatrypaea Poore, Dworschak, Robles, Mantelatto & Felder, 2019 was found in the northern South China Sea. Poore et al. (2019) established the genus Pugnatrypaea on the basis of molecular phylogenetic analyses  including P. emanata  (therein = "Pugnatrypaea GMX") and P. pugnatrix (de Man, 1905), which together formed a clade; another five species were included in the genus. All seven species share the diagnostic characters including the shape of the third maxilliped merus, third pereopod propodus, uropodal exopod, and telson. Most strikingly, the telson tapers over its distal one-third and ends in a pair of posterior lobes separated by a notch with a medial spine.

Materials and methods
All specimens examined have been deposited in the Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China (IOCAS). The drawings were made with the aid of drawing tube mounted on a Zeiss Stemi Sv11 compound microscope. Carapace length (cl.) was measured from the tip of the rostrum to the posterior margin of the carapace. Diagnosis. Carapace with narrow triangular spiniform rostrum, reaching at least proximal 2/3 of eyestalk in dorsal view; dorsal oval well defined. Eyestalk elongate, subrectangular, distomedial corner produced into rounded prominence, cornea well defined. Antennular peduncle much shorter than antennal peduncle. Third maxilliped lacking exopod, row of spines forming distinct crista dentata on internal surface of ischium. Male major cheliped merus lacking proximal hook on lower margin, instead with nine minute spines on middle part. Pleomeres smooth dorsally, dorsal tergite fused with the lateral pleuron, pleomere 2 distinctly longer than other pleomeres. Pleopod 1 uniramous, pleopod 2 biramous in both males and females. Third through fifth pleopodal endopods each with slender, finger-like appendix interna extending clearly beyond margin. Telson elongate, subrectangular, posterior margin distinctly bilobate, lobes posteriorly separated by deep incision accommodating distinct median spine. Uropodal endopod broad, ~1.1× longer than broad, with spiniform setae near anterior and distal margins and a movable spine near posterolateral angle; exopod ~1.2× as long as wide, anterodistal corner rightangled, posterodistal margin with row of 6-8 long, blade-like setae proximal to long setae on distal margin.
Pereopods 1 unequal and strongly dissimilar, major cheliped located on either right or left side, shape, and ornamentation sexually dimorphic. Male major cheliped massive (Fig. 3A). Ischium 2.8× as long as high; upper margin sinuous, unarmed; lower margin slightly convex, armed with row of nine inconspicuous subequal spines. Merus as long as ischium, 1.8× as long as high; upper margin slightly convex, unarmed; lower margin sinuous, with row of nine minute spines on middle part, the middle one largest. Carpus elongated, 0.7× as long as high, 0.7× as long as merus; upper margin almost straight; proximo-lower margin gently convex, unarmed. Chela ~2.0× as long as high; palm subquadrate, ~1.3× as long as high, 1.9× as long as carpus; fixed finger 0.6× as long as palm, cutting edge with some inconspicuous denticles basally; dactylus slightly curved distally, slightly longer than fixed finger, cutting edge sinuous, armed with row of inconspicuous denticles and a large round denticle in the middle.
Male minor cheliped (Fig. 3B) shorter and much more slender than larger cheliped. Ischium ~4.0× as long as high, upper margin nearly straight, unarmed, lower margin with row of nine inconspicuous subequal spines. Merus 0.9× as long as ischium, ~2.4× as long as high, upper and lower margins slightly convex, lower margin with a small upper-middle spine; outer surface medially swollen. Carpus 3.5× as long as high, 1.4× as long as merus, abruptly narrowed at base; upper margin almost straight; proximo-lower margin convex. Chela with narrow gap between slender dactylus and fixed finger; palm nearly 1.5× as long as high, 0.5× as long as carpus; fixed finger tapering distally to acute tip, cutting edge unarmed; dactylus slightly longer as palm, slender, unarmed on concave cutting edge.
Female major cheliped ( Fig. 3C) with ischium 3.5× as long as high, upper margin slightly sinuous; lower margin almost straight, with row of five inconspicuous subequal spines. Merus ~0.9× as long as ischium, upper margin slightly convex, unarmed; lower margin slightly convex, with three small spines at mid length. Carpus broad, subquadrate, 1.2× as long as high, 0.9× as long as merus; upper margin almost straight, lower margin keeled. Chela similar to that of male but relatively smaller; palm subquadrate, ~1.5× as long as high; fixed finger 0.7× as long as palm, cutting edge with a wide triangular denticle on middle; dactylus slightly longer than fixed finger, cutting edge sinuate and with two round denticles on proximal half. Minor cheliped in female similar to that of male and ~0.8× as long as major cheliped.
Pereopod 2 (Fig. 3D) chelate. Ischium 1.8× as long as high; merus ~3.3× as long as high, upper margin smooth, lower margin protruding and with row of dense long setae; carpus subtriangular, shorter than merus; chela slightly shorter than carpus, with dense setae on lower and upper margins; palm with upper margin slightly convex; dactylus 2.3× as long as upper margin of palm; carpus and chela fringed with short to long setae along margins.
Remarks. Pugnatrypaea ruiyui sp. nov. is the eighth species assigned to the genus Pugnatrypaea on account of the spiniform rostrum; telson anterolateral lobe obsolete, undefined, tapering over distal 1/3 ending in pair of posterior lobes separated by notch, with medial spine.
The morphological separation of Pugnatrypaea ruiyui sp. nov. from its congeners draws upon the work of Bate (1888), de Man (1928a, 1928b), Sakai (19992010;2011), Sepahvand et al. (2015, . The new species is closely related to P. intermedia and P. lobetobensis in lacking a proximal hook on the lower margin of the male major cheliped merus, whereas P. pugnatrix, P. iranica, and P. emanata bear a proximal hook, but it can be distinguished from latter two in having the upper margins of the meri of both chelipeds meri (versus with proximal spines). Unfortunately, both P. bicauda and P. orientalis are known from only single, apparently incomplete specimens that lack both chelipeds. The new species can be distinguished from P. bicauda by the biramous male pleopod 2 (versus uniramous) and differs markedly from P. orientalis in having the rostrum shorter than the eyestalks (versus rostrum slightly extending beyond the tip of the eyestalks).