Description of Parvocalanus leei sp. n. (Copepoda, Calanoida, Paracalanidae) in Western Korea, with comments on the taxonomic position of Paracalanus arabiensis Kesarkar & Anil, 2010

Abstract A new species of paracalanid calanoid copepod Parvocalanus leei sp. n., is described from specimens collected in shallow waters of Western Korea. The new species is closely similar to Parvocalanus arabiensis (Kesarkar & Anil, 2010), Parvocalanus crassirostris (F. Dahl, 1894), Parvocalanus latus Andronov, 1972, and Parvocalanus scotti (Früchtl, 1923) in having two short terminal spines on the distal segment of the fifth leg and a similar rostrum in the female, but can be readily distinguished from its congeners by the body size, relative length of antennules, segmentation of endopod of leg 1, and pattern of ornamentation of spinules on legs 1 to 4 in the female. The taxonomic position of Parvocalanus arabiensis and the validity of the genus Parvocalanus Andronov, 1970 are also discussed.


Introduction
Most of the species of the family Paracalanidae Giesbrecht, 1892 are distributed across both northern and southern hemispheres, with about 80 species in eight genera having been described thus far (Boxshall and Halsey 2004;Vives and Shmeleva 2007;Bradford-Grieve 2008). Six out of the eight paracalanid genera accounting 12 species have been recorded thus far in Korean waters (Acrocalanus Giesbrecht, 1888, Bestiolina Andronov, 1991, Calocalanus Giesbrecht, 1888, Mecynocera I. C. Thompson, 1888, Paracalanus Boeck, 1865, and Parvocalanus Andronov, 1970 (Yoo 1995;Soh et al. 2013). The genus Parvocalanus Andronov, 1970 contains six valid species (Boxshall and Halsey 2004). It is one of the major constituents of the calanoid assemblage of shallow waters worldwide (Robertson et al. 1988;Beltrão et al. 2011;Chen et al. 2011). They are generally smallsized, varying from 0.5 to 1.5 mm in body length, and play an important role as primary consumers in marine ecosystems (Araujo 2006;Lenz 2012). In Korean waters, two species of Parvocalanus have been reported thus far: Parvocalanus crassirostris (F. Dahl, 1894) (as Paracalanus crassirostris) (Yoo, 1995) and Parvocalanus elegans Andronov, 1972(Soh et al. 2013. They share many of the characteristics of Paracalanus Boeck, 1865, but differ in the following features: a short, blunt rostrum; short terminal spines on the distal segment of female P5; and absence of dorsal hump in the male (Andronov 1970). These prominent features were used by Andronov (1970) to transfer Paracalanus crassirostris, P. dubia, P. scotti, and P. serratipes to the genus Parvocalanus. However, most of Parvocalanus species are difficult to identify because of their similar aspect and poor original descriptions.
During an investigation of planktonic copepods collected in shallow waters of Western Korea, we identified a new species of Parvocalanus which had been previously overlooked. In this study, we describe it and provide keys to all genera of Paracalanidae and species within Parvocalanus. Additionally, we evaluate the taxonomic position of Paracalanus arabiensis Kesarkar & Anil, 2010.

Materials and methods
Copepods were collected in shallow waters at Mokpo, Western Korea ( Fig. 1), on 23 August 2013 with a 0.2 mm mesh-size plankton net. For morphological examination, samples were fixed in 5% natural formalin-seawater solution, and later cleared in 70% lactic acid for 1 to 2 hours before dissection in a drop of lactophenol using a wooden slide procedure (Humes and Gooding 1964). Dissected body parts and appendages were examined under a compound microscope up to × 1,000. Drawings were made with the aid of a drawing tube equipped on the microscope. Body size of individuals was measured from the head to tip of the caudal rami excluding caudal setae using a stage micrometer. Morphological terminology followed Huys and Boxshall (1991). Abbreviations used in text and figures are as follows: s, seta; ae, aesthetasc; P1-P5, legs 1 to 5, respectively. Specimens are deposited in the National Institute of Biological Resources (NIBR), Incheon, Korea. Type material. Adult female holotype, 0.93 mm (NIBRIV0000302101) and adult male allotype, 0.62 mm (NIBRIV0000302102) preserved undissected in 70% ethanol, collected from the Yellow Sea, Korea (34°46'10"N, 126°20'24"E). Paratypes: 20 females (NIBRIV302103) and 10 males (NIBRIV302104) preserved in 70% ethanol, 21 August 2013. Dissected paratypes (5 females, 3 males) are kept in collection of the senior author. Description below is based on paratypes.
Type locality. Shallow waters of Mokpo (34°46'10"N, 126°20'24"E), Western Korea. Etymology. The species is named after Mrs. Jungah Lee, wife of senior author (S.Y. Moon), as a small token of appreciation for her encouragement and support to senior author.
Swimming legs seta and spine formula and ornamentation ( Fig. 6A-D) generally as in female, but with some differences, as follows: P1 (Fig. 6A) lacks posterior spinules on coxa, the basis and endopod are unadorned, and the third exopodal segment lacks of row of spinules on posterior surface; P2 (Fig. 6B) has the second and distal endopodal segments with denticles on outer edge; distal endopodal segment without row of spinules on mediolateral margin; P3 (Fig. 6C) has the second and distal endopodal segments with denticles on outer edge; second exopodal segment without row of spinules on the posterodistal margin; and P4 ( Fig. 6D) has the second and distal endopodal segments with denticles on outer edge; and first exopodal segment without row of spinules on the anterodistal margin. P5 (Fig. 6E) strongly asymmetrical and uniramous: right P5 5-segmented and longer than second urosomal segment; basis and first exopodal segment unarmed; second exopodal segment with pointed process on distomedial angle; distal segment with two pointed processes, inner tiny. Left leg 3-segmented; distal segment with tiny outer apical spine, inner apical spine long, 9 times as long as outer spine.
Variation Remarks. The adult female of Parvocalanus leei sp. n. is very similar to P. arabiensis (Kesarkar & Anil, 2010), P. crassirostris, P. latus Andronov, 1972, andP. scotti (Früchtl, 1923). All them share the short and blunt rostrum and the elongate distal segment of P5, with the inner terminal spine less than three times the length of the outer terminal spine. Nevertheless, the new species differs from P. arabiensis as follows: (1) the body length is higher than 0.7 mm in the new species, but less than 0.7 mm in P. arabiensis; (2) the antennule extends up to the medial margin of third urosomite in the new species, but only to the posterior margin of genital double-somite in P. arabiensis; (3) the endopod of P1 is unsegmented in the new species, but 2-segmented in P. arabiensis; (4) the inner spine of P5 is less than 1.7 times longer than outer terminal spine of P5 in the new species, but more than 1.7 times longer than in P. arabiensis; and (5) there is no ornamentation of denticles on the distal edge of the third exopodal segment of P4 in the new species, vs. denticles present in P. arabiensis.
The female of Parvocalanus leei closely resembles P. crassirostris, but is larger (more than 0.7 mm in length compared to less than 0.7 mm); the fourth and fifth pedigerous somites are separated (vs. partially fused in P. crassirostris); the antennules extend to the medial margin of anal somite (vs. approximately to second urosomite in P. crassirostris);   the length/width ratio of the distal segment of P5 is lower than 2.5 (vs. more than 3 in P. crassirostris); and there is a row of spinules on the distal end of the second segment of P5 (vs. row absent in P. crassirostris).
The new species shares with Parvocalanus latus the similar body shape and the P5 ornamentation in the female, but differs in the following features: (1) the body is more than 0.7 mm in length (vs. less than 0.7 mm in P. latus); (2) the antennule is comparatively shorter, reaching only the medial margin of anal somite (vs. reaching the end of caudal rami in P. latus); and (3) the genital double-somite is swollen anterolaterally in the new species (vs. somite not swollen in P. latus).
The female of Parvocalanus leei can be readily differentiated from Parvocalanus scotti based on the following features: (1) the body is more than 0.7 mm (vs. less than 0.7 mm in P. scotti); (2) the antennule extends only to the medial margin of anal somite (vs. to the distal margin of caudal rami in P. scotti); (3) the length/width ratio of caudal rami is higher than 2 in the new species (vs. less than 2 in P. scotti), and (4) the length/width ratio of second segment of P5 is less than 3 (vs. more than 3 times in P. scotti). Kesarkar and Anil (2010) distinguished between Paracalanus Boeck, 1864 and Parvocalanus based on the following characteristics of the female, because all species had been previously described based only on the female: (1) basis of P1 with inner edge seta (vs. without inner edge seta in Parvocalanus); (2) P1 endopod 2-segmented (vs. endopod unsegmented or 2-segmented in Parvocalanus); and (3) second endopodal segment of P1 with 5 setae (vs. 6 setae in Parvocalanus). But these characteristics overlap in the two genera. Indeed, the genus Parvocalanus shows many similarities with Paracalanus, but differs in the following features: (1) rostrum short, broad and bifurcated in both sexes; (2) distal segment of P5 terminal spines short in the female; and (3) absence of a medial keel-like dorsal hump on the cephalosome of male. However, five species of Parvocalanus have been described and/or illustrated as having an inner seta on the basis of P1, namely: P. arabiensis, P. dubia, P. leei sp. n., P. scotti, and P. serratipes. A molecular phylogeny recently published discriminated the genera Parvocalanus and Paracalanus with well-supported nodes, with Parvocalanus placed as sister to the rest of paracalanid genera (Cornils and Blanco-Bercial 2013). But the morphological phylogeny assessed in parallel by the same authors failed to separate the two genera (Cornils and Blanco-Bercial 2013), although it should be remarked that the morphological dataset used was extremely poor due to the poorness of the original species descriptions.

Discussion
Parvocalanus leei is distinguished from the rest of members of its genus based on the following characteristics of the female: fourth and fifth pedigerous somites completely separated, large size (more than 0.7 mm), and presence of spinules on the distal end of distal segment of P5. These differences are shown in Table 1. In the present study, we have re-examined the following combination of female features in order to separate species: (1) body shape and size; (2) relative length of antennule; (3) fusion of fourth and fifth pedigerous somites; (4) presence/absence of spinules on second   endopodal and exopodal segments of P2 and P4; (5) presence/absence of spinules on distal end of distal segment of P5; (6) length/width ratio of second segment of P5; and (7) length ratio between inner and outer terminal spines of P5. Parvocalanus crassirostris was originally described by F. Dahl (1894) as Paracalanus crassirostris from the mouth of the river Tocantins, Brazil, but the description was rather incomplete and based on the female only (see F. Dahl 1894: taf. I, figs 27 and 28). The populations of this species from estuarine and shallow waters of Korea closely resemble the Brazilian population, both having two short apical spines on the distal segment of P5, but the female of P. leei is larger than P. crassirostris, its fourth and fifth pedigerous somites are completely separated and the length/width ratio of distal segment of its P5 is lower (see Table 1). The populations of P. crassirostris from Japanese waters are very similar to P. leei, but differ in having an inner seta on the coxa of P1 in both sexes, a distal segment of female P5 devoid of a distal row of spinules, the male left P5 is 3-segmented (N=5) with the long apical spine (39 µm) 6.5 times as long as the short outer spine (6 µm), and the body is larger in both sexes (see Hiromi 1981). Parvocalanus crassirostris has a worldwide distribution throughout temperate and tropical regions (Razouls et al. 2005(Razouls et al. -2014 despite its morphological homogeneity. Kesarkar and Anil (2010) described the populations of this species from the Mondovi and Zuari estuaries, Goa, West coast of India, as a new species Parvocalanus arabiensis (Kesarkar and Anil 2010). However, these authors might have overlooked some previous morphological studies of P. crassirostris (Tanaka 1960;Shen and Lee 1963;Hiromi 1981;Bradford-Grieve 1994). Additionally, most of the Parvocalanus species were not described following modern standards and most of them need to be redescribed. Thus, the taxonomy, morphological variability and distribution of P. crassirostris is not well understood. These facts suggest that a more detailed research on its geographical variation in terms of morphological and molecular features is necessary for a better understanding of its evolutionary history.

Taxonomic review on Paracalanus arabiensis Kesarkar & Anil, 2010
Paracalanus arabiensis was originally described by Kesarkar and Anil (2010) based on 11 adult females collected from Mondovi and Zuari estuaries, Goa, west coast of India. The assignment of this taxon to Paracalanus was based on the examination of the literature, where figures of some of the presumed diagnostic features of the genus, such as presence of inner edge seta on basis of female P1, P1 endopod 2-segmented, and second endopodal segment of P1 with 5 setae were shown. However, it shares the generic characteristics of Parvocalanus (see Andronov 1970;Hiromi 1987;Boxshall and Halsey 2004). Two major differences between P. arabiensis and the members of Parvocalanus are the presence of inner seta on the basis of P1, and of a 2-segmented endopod in P1 with 5 setae on the distal segment in the former species. Since the presence or absence of inner seta on the P1 basis has been historically used to define some species of Parvocalanus, we believe this feature is not relevant enough as to put this Arabian taxon in a genus different to Parvocalanus. We consider more appropriate to slightly modify the generic diagnosis of Parvocalanus to include "basis of P1 with or without inner seta" and "endopod of P1 unsegmented or 2-segmented" to accommodate P. arabiensis within this genus. Parvocalanus arabiensis (Kesarkar & Anil, 2010), comb. n. resembles P. crassirostris in the small body size, the short and bifurcate rostrum, ending in two acute points, and in the presence of two short terminal spines on the female P5. But they can be readily distinguished based on rostrum appearance; the relative length of terminal spines of female P5; and the presence/absence of a medial keel-like dorsal hump on the cephalosome of male.