A new species of Labidocera (Copepoda, Calanoida, Pontellidae) collected from Okinawa, southwestern Japan, with establishment of five Indo-West Pacific species groups in the L. detruncata species complex

Abstract Labidocera churaumi sp. n. is described from Okinawa, southwestern Japan. The female of the new species differs from other congeners in genital compound somite with right postero-lateral and left antero-lateral processes. The male is distinguished from other congeners by the structure of the fifth leg. This new species is assigned to a newly proposed species group, the Labidocera madurae species group, within the Labidocera detruncata species complex. In this species complex five Indo-West Pacific species groups are recognized (cervi, detruncata, gangetica, madurae, and pavo) and defined on the basis of difference in sexual dimorphism.


Introduction
We have been carrying out intensive faunistic surveys of marine invertebrates around the Nansei Islands, in the subtropical region of southwestern Japan, since 1988 and have discovered many new crustacean taxa, especially copepods. For example the copepod order Platycopioida was first reported from the Indo-Pacific in this region in 1994 (Ohtsuka and Boxshall 1994). The systematics of shallow-and deep-water copepods from these waters, have been a major focus of research and some of discoveries have been important in elucidating aspects of the evolutionary history and zoogeography of copepods (Barr and Ohtsuka 1989, Ohtsuka et al. 1991, 1996, 2002, 2003, 2004, 2005, Barthélémy et al. 1998.
In May 2011 we found an undescribed species of the calanoid genus Labidocera Lubbock, 1853 (Family Pontellidae) from Okinawa Island and neighboring islands. It clearly belongs to the L. detruncata species complex (Fleminger 1967, Greenwood and Othman 1979, Mulyadi 2002, due to its characteristic sexual dimorphism. This species complex mainly consists of coastal species from tropical and subtropical Indo-West Pacific waters and also two Atlantic species (Fleminger 1967, Greenwood and Othman 1979, Mulyadi 2002. The present paper provides a description of the new species, and remarks on species groups within the detruncata species complex.

Materials and methods
A fish collection light (KU-5MB, MW50S-G, KOTO electric Co., Ltd.) was deployed at Naha Port (May 2011) and Tokashiki Port (May 2011) after sunset. Conical plankton nets (diameter 30 cm, mesh size 0.1 mm) were towed around the light several times. Copepod specimens were fixed with 10% neutralized formalin/seawater or 70% ethanol immediately after collection. Copepods were dissected under a binocular microscope and examined and illustrated using a compound microscope fitted with differential interference contrast lighting (Optiphoto, Nikon Co., Ltd.) and a drawing tube.
In describing the features of the new species, we have followed the terminology of Huys and Boxshall (1991). We followed Fleminger (1967) and Fleminger et al. (1982) about species complexes (=superspecies) and groups in the genus Labidocera.

Systematics
Female. Body (Fig. 1A, B) length of females ranging between: 2225 and 2790 µm (average 2475 µm, n=29), measured from frontal margin of cephalosome to end of caudal rami excluding caudal setae. Ratio of prosome to urosome lengths 4:1, prosome length to width ratio 2.85:1. Cephalic profile rounded in dorsal view, without lateral cephalic hooks. Paired dorsal eyes with cuticular lenses; protuberant ventral eye extending anteroventrally between rostral processes (Fig. 1C). Rostrum bifid, directed posteroventrally. Posterior margins of prosome almost symmetrical in dorsal view, tapering to simple abbreviated, pointed process at each lateral corner. Urosome 2-segmented of highly characteristic shape. Genital compound somite strongly asymmetrical; anterior left surface with posteriorly-directed rod-like process and posterior right smoothly rounded. Spermatophore (Fig. 1D) attached dorsally to genital compound somite.
Left antennule, antenna, mouthparts and swimming legs as in female. Leg 5 (Fig. 4D) asymmetrical. Left leg 5 short; intercoxal sclerite and left coxa fused. Basis cylindrical with seta near base. Exopod 2-segmented: first segment cylindrical; second segment triangular short with protruding hairy medial surface and 3 distal and 1 lateral spines, one of them long. Right leg 5 basis with seta. Exopod 2-segmented, forming chela; thumb of chela large, triangular, arising near base of first exopodal segment. First exopodal segment with 2 small setae. Second exopodal segment elongate and curved, with 3 slender marginal setae.
Remarks. The present new species is similar to Labidocera madurae Scott, 1909 andL. tasmanica Taw, 1974 in having the following features: (1) the posterolateral margins of the prosome are symmetrical, each triangular with a sharply pointed tip; (2) the female urosome is moderately or markedly asymmetrical; (3) the caudal rami are symmetrical and not highly modified; (4) the endopods of female leg 5 are nearly symmetrical, short, conical, and not bifid at the tip; (5) the thumb of the right leg 5 of the male is triangular with a broad base, and is slightly recurved; (6) the distal part of terminal segment of the left leg 5 of the male bears 3 spines, the outermost of which is the longest. These 3 species constitute a species group within the Labidocera detruncata species complex (see Discussion). Labidocera churaumi sp. n. can be dis-tinguished from L. madurae and L. tasmanica by: (1) the presence of right posterolateral and left antero-lateral processes on the female genital compound somite; (2) the exopod of the female leg 5 is very short, only as long as the basis, and has a bi-  Etymology. The new specific name "churaumi" is from an Okinawan dialect, meaning the beautiful seas around the type locality Okinawa. Fleminger (1967) classified species of the genus Labidocera into four superspecies (=species complex), the L. wilsoni Fleminger & Tan, 1966, L. detruncata (Dana, 1849, L. darwini Lubbock, 1853, and L. kroyeri (Brady, 1883) species complexes, but left some species unassigned. Within the L. detruncata species complex he recognized nine species. Subsequently Greenwood and Othman (1979) added further three species to this species complex, and compared nine Indo-West Pacific members of the species complex, but did not consider three species: L. orsinii Giesbrecht, 1889, L. gangetica Sewell, 1934 andL. nerii (Krøyer, 1849) that Fleminger (1967) originally assigned to this species complex. Subsequently Greenwood and Othman (1979) and Othman (1986) added new species: L. farrani Greenwood &Othman, 1979 andL. jaafari Othman, 1986 to the species complex. Mulyadi (2002) was the first to define the Indo-West Pacific species group within the L. detruncata species complex which he referred to as L. detruncata species group, in which were accommodated the following ten species: L. detruncata, L. pavo Giesbrecht, 1889, L. bataviae Scott, 1909, L. madurae Scott, 1909, L. cervi Krämer, 1895, L. caudata Nicholls, 1944, L. sinilobata Shen & Lee, 1963, L. tasmanica Taw, 1974, L. farrani Greenwood & Othman, 1979, and L. jaafari. One remaining issue is that two Atlantic species (L. orsinii and L. nerii) and the Indian species (L. gangetica) were not assigned to this species complex by Mulyadi (2002). Here we reinstate Fleminger's (1967) inclusion of the two Atlantic species (L. orsinii and L. nerii) and the Indian species (L. gangetica).

Discussion
Therefore Mulyadi's (2002) definition of the Indo-West Pacific L. detruncata species group needs some emendations as follows: (1) the posterolateral prosomal corners of both sexes protrude posteriorly into a pointed tip; (2) the female urosome is slightly or distinctly asymmetrical, about 1/6 to 1/4 as long as prosome, and 2-or 3-segmented; (3) the rostrum of both sexes is widely divided; (4) the caudal rami of the female are slightly or remarkably asymmetrical, broadened, with or without one or more thickened setae; (5) the exopods of female fifth legs are asymmetrical, with each bearing 3 lateral and 2 terminal processes; (6) the endopods of female fifth legs are either simply conical (rarely bifid) distally or are totally reduced; (7) the thumb of the right leg 5 of the male is conical or spatulate; (8) the finger of the right leg 5 of the male is slender; (9) the terminal segment of the left leg 5 of the male bears 1 outer and 3 slender terminal (rarely thick in L. caudata) elements. Since the two Atlantic and L. gangetica comply with this emended diagnosis, Fleminger's (1967) original L. detruncata species complex (Mulyadi's (2002) Indo-West Pacific L. detruncata species group plus L. orsinii, L. nerii and L. gangetica) is well defined by this amended diagnosis.
Although Mulyadi (2002) defined the Indo-West Pacific L. detruncata species group (the ten species listed above), it can be further subdivided into the following five newly proposed species groups on the basis of variation in the differing expressions of sexual dimorphism. Labidocera sinilobata, L. jaafari and L. gangetica share synapomorphies in variation in the differing expressions of sexual dimorphism, viz., (1) the absence of endopods from leg 5 of the female, (2) the thumb and finger of the right leg 5 of the male slender, (3) there is a rounded process present basal to the thumb of the right male leg 5, and (4) there is a protrusion on the inner surface of the terminal segment of the left male leg 5. These three species have a restricted distribution in the subtropical and tropical, coastal waters of the Indo-West Pacific (Sewell 1912, Shen and Lee 1963, Silas and Pillai 1973, Othman 1986, Mulyadi 2002, Razouls et al. 2014, and are referred to here as L. gangetica species group (Fig. 5).
Two species, L. cervi and L. caudata from Oceania are unusual in both having a triangular process distally on the terminal segment of the male left leg 5. The first exopodal segment of male leg 5 bears an outer subterminal process in both species, although it is not certain whether these are homologous. In the female the exopod of leg 5 bears 3 distinct lateral and 2 terminal prominences, while the endopod is simply spiniform. The posterolateral prosomal corners of L. cervi are remarkably large compared to those of L. caudata. These two species are considered here as the L. cervi species group. McKinnon and Kimmerer (1984) pointed out the similarity in the fifth legs of both sexes of L. caudata and L. madurae, but we regard the unique structure of the terminal exopodal segment of the male left leg 5 as a robust synapomorphy to define the species group.
Labidocera detruncata is most closely related to L. farrani in sharing the following synapomorphies: (1) the complex, dorsal swelling on the genital compound somite of the female; (2) the anal somite of the female protruded mid-posteriorly; (3) the caudal rami of the female are widely separated, and the right ramus is larger than the left; (4) the basis of the female leg 5 is swollen; (5) the male right leg 5 has a spatulate thumb; (6) the terminal segment of the male left leg 5 has 4 elements, the second outermost of which is the longest. These two species belong to L. detruncata species group sensu stricto. Labidocera detruncata is widely distributed in oceanic waters of the Indo-Pacific and West Atlantic regions, while L. farrani has a distribution in coastal waters of Indo-West Pacific (Silas and Pillai 1973, Greenwood and Othman 1979, Mulyadi 2002, Jeong et al. 2009, Razouls et al. 2014 (Fig. 5).
Labidocera pavo and L. bataviae share the following features in the female: (1) the female caudal rami are broadly separated and posterolaterally expanded; (2) the exopod of the female leg 5 is slender, with 3 lateral and 2 terminal distinct prominences; (3) the endopod of the female leg 5 is short, at most 1/3 to 1/4 as long as the exopod; (4) the thumb of the first exopodal segment of the male right leg 5 is bifid; (5) the terminal exopodal segment of the male left leg 5 is slender, and carries 3 fine elements. These two species belong to the L. pavo species group and they are broadly distributed in coastal waters of the temperate to tropical Indo-Pacific regions (Silas andPillai 1973, Razouls et al. 2014) (Fig. 5).
As already mentioned in "Remarks", L. madurae, L. tasmanica and L. churaumi sp. n. together belong to the L. madurae species group. This species group has a restricted distribution in tropical to temperate waters of the Indo-Pacific (Scott 1909, Silas and Pillai 1973, Taw 1974, Razouls et al. 2014 (Fig. 5). Labidocera detruncata is widely distributed in the Indo-West Pacific, while L. pavo has a narrow coastal distribution in the region. In addition L. sinilobata is restricted to the West Pacific, whereas L. gangetica occurs in the Indian Ocean. Such restricted distributions within this species complex suggest us the possibility of parallel speciation due to the isolation mechanism by the existence of Sundaland during the glacial periods (cf. Fleminger 1986).