A new species of the genus Cristimenes Ďuriš & Horká, 2017 (Decapoda, Caridea, Palaemonidae)

Abstract A new species of crinoid-associated shrimp, Cristimenesbruceisp. nov., is described based on specimens from Korea, although the species also occurs in Hong Kong and is likely more widespread. The new species is morphologically very similar to C.commensalis, but can be distinguished by the reduced supraorbital tooth on the carapace. Cristimenesbruceisp. nov. is clearly recovered as a monophyletic species through COI barcode and molecular phylogenetic analyses based on four genetic markers (COI, 16S, H3, 18S).

Cristimenes commensalis differs from the other two species by its host affiliation and can also be easily distinguished by the morphology of the ambulatory dactyli (Bruce 1965(Bruce , 1967Ďuriš and Horká 2017). The species has been recorded from various host crinoid species across the Indo-West Pacific, after it was described from Murray Island, Torres Strait, Australia in 1915 (Barnard 1958;Bruce 1982b;Marin and Savinkin 2007). Bruce (1979) already remarked upon variation in the supraorbital tooth and the lateral carina of specimens from Hong Kong in comparison to Indonesian specimens (Bruce 1982a(Bruce , 1983. Specimens matching this morphology were obtained from Korea, and based on a morphological comparison as well as a molecular analysis are herein reported as a new species.

Materials and methods
Fieldwork for this study was carried out and organised in Korea (2012Korea ( -2018, the Philippines (2014, 2018), and Vietnam (2016-2018 by Seoul National University (SNU), Korea Institute of Ocean Science and Technology (KIOST), the University of the Philippines Visayas (UPV), and the Institute of Tropical Biology (ITB). Host crinoids were collected during scuba diving and associated shrimps separated. All shrimps and tissue of host crinoids were preserved in 80% ethanol. The type series is deposited in the Marine Arthropod Depository Bank of Korea, Seoul National University, Seoul, Korea (MADBK); National Institute of Biological Resources, Incheon, Korea (NIBR) and the Oxford University Museum of Natural History, Oxford, United Kingdom (OUMNH.ZC). Postorbital carapace length (pocl, in mm) is used as the standard size measurement.
Antennule (Fig. 3B) well developed; basal segment with two acute distolateral teeth, with submarginal medioventral tooth; stylocerite reaching to middle of proximal segment; intermediate and distal segment subequal in length; upper flagellum biramous, proximal four segments fused, shorter free ramus with five segments, 0.3 of longer free ramus. Antenna (Fig. 3C) well developed; basicerite with sharp distoventral tooth; ischiocerite and merocerite unarmed; carpocerite reaching to 0.4 of scaphocerite; scaphocerite 2.4 times as long as maximal wide, distolateral tooth large, not reaching distal end of lamellae.
First pereiopod (Fig. 5A, B) overreaching distal end of scaphocerite; ischium 0.56 length of merus, unarmed; merus and carpus subequal in length; carpus 1.36 times length of chela with row of serrulate setae along distomesial margin; chela 1.9 times longer than deep; palm with transverse row of serrulate setae ventrolaterally; fingers subspatulate, 0.89 times length of palm, cutting edge straight, entire, with groups of setae.
Pleopods as usual for genus. First pleopod of male ( Fig. 7A) with endopod 2.8 times longer than wide. Second pleopod of male (Fig. 7B) with appendix masculina with stout, long setae; appendix interna slightly longer than appendix masculina. Second pleopod of female (Fig. 7C) as usual for genus. Uropod (Fig. 2E) overreaching distal end of telson; exopod with distolateral tooth and movable acute spine.
Etymology. The new species is named in honour of Dr AJ (Sandy) Bruce, in recognition of his considerable contribution to the systematics of Palaemonidae.
Colour. Body colour (Fig. 8A, B) orange or reddish-brown adapted to the colour of the host crinoids; creamy white line extending from the tip of the rostrum to the posterior dorsal margin of the carapace; similar, but thinner and lighter line extending from posterior ventral angle of the sixth abdominal segment to the lateral side of the first antennular peduncle.
Ecology. The specimens were collected from the crinoids Anneissia japonica, A. solaster and Catoptometra rubroflava at a depth of 15 -27 m. Bruce (1982a) reported that the Hong Kong specimens were collected from Tropiometra afra (Hartlaub, 1890).
Distribution. Presently only known from the type locality, Jeju Special Self-Governing Province, Korea as well as Hong Kong (Bruce 1982a).
Remarks. The new species is morphologically very similar to the other crinoid-associated species in the genus, C. commensalis (Fig. 8C). Within the genus, both species share the following characteristics: subspatulate fingers of the first pereiopods; proximally dentate and distally serrate cutting edges of the fingers of the second pereiopods (Fig. 10C,  D); and the presence of accessory spinules on the anterior margin of the dactyli of the ambulatory pereiopods. The new species can, however, be easily distinguished from C. commensalis by the reduced, blunt supraorbital tooth ( Fig. 9A-C) and reduced rostral carinae (vs. well-developed supraorbital tooth (Fig. 9D) and rostral carinae in C. commensalis).
Cristimenes brucei sp. nov. can easily be distinguished from the echinoid-associated species C. cristimanus (Fig. 8D) and C. zanzibaricus by the reduced supraorbital tooth and rostral carinae (vs. extremely developed supraorbital tooth and rostral carinae), the presence of accessory spinules on the anterior margin of the ambulatory dactylus (vs. absent), and a different host affiliation, with the latter two species being associated with echinoids.
The crinoid-associated genera Araiopontonia Fujino & Miyake, 1970, Laomenes Clark, 1919, and Unguicaris Marin & Chan, 2006 are phylogenetically closely related to Cristimenes. The new species shares a morphological trait with Araiopontonia odontorhyncha Fujino & Miyake, 1970 in having accessory spinules on the anterior margin of the ambulatory dactylus, but the new species can easily be distinguished from A. odontorhyncha by the reduced supraorbital teeth and rostral carinae, the presence of a hepatic tooth on the carapace, and the low and rounded epistome (vs. developed supraorbital tooth and rostral carinae, absence of hepatic tooth, and well developed rounded epistomial horns in A. odontorhyncha). All species in the genus Laomenes can  (Borradaile, 1915) from Vietnam (SNU VI VI305) D Cristimenes cristimanus (Bruce, 1965) from Vietnam (SNU VI VI297).
be distinguished from the new species by having more strongly developed supraorbital teeth and rostral carinae, well developed sharp epistomial horns and simple biunguiculat ambulatory dactylus. The new species is morphologically similar to U. novaecaledoniae (Bruce, 1968) among species of the genus Unguicaris. The new species shares with U. novaecaledoniae similar first chelipeds, proximally dentate but distally serrate cutting edges of the fingers of the second pereiopods, and the presence of well-developed accessory spinules on the anterior margin of the ambulatory dactyli. The new species can, however, be distinguished from U. novaecaledonia by the presence of reduced supraorbital teeth (vs. absent).
Phylogenetic analyses were conducted on 21 specimens of seven species of four genera ( Table 1). The combined 2068 bp fragments had 253 parsimony-informative sites for COI, 145 for 16S, 42 for H3, and 102 for 18S. The ML and BI analyses showed the same topology, except for Laomenes and Unguicaris (Fig. 11). The resulting phylogeny clearly indicates the monophyly of Cristimenes with high support values, both in ML and BI analyses. Cristimenes brucei sp. nov. is clearly recovered as a monophyletic species but as a sister group to the echinoid associated C. cristimanus, whilst the crinoid associated C. commensalis is a sister group to the clade containing C. brucei sp. nov., C. cristimanus, and C. zanzibaricus.