Two new species of the genus Emertonia Wilson, 1932 from Korean waters (Copepoda, Harpacticoida, Paramesochridae)

Abstract Two new species of the genus Emertonia were found from the west coast of Korea. The first new species, E. koreana sp. n., is closely related to E. acutifurcata. However, the new species is clearly distinguished by the presence of two modified pinnate setae on the P5 baseoendopodal lobe. All body somites of the new species except for the last two urosomites have strongly developed hyaline frills forming quadrilateral lappets. The second new species, E. simplex sp. n., superficially resembles E. mielkei in the structure of antennary exopod (with five setae), and the shape of P5. However, this new species differs from its congener mainly by having a caudal ramus 3.5 times as long as width, and P1 enp-2 with two claw-like setae. In addition, a key to the worldwide species of Emertonia is provided.


Introduction
The family Paramesochridae consists of 13 genera and more than 150 species distributed worldwide. Within the family, the genus Emertonia Wilson, 1932 is seen to be the most species-rich genus. Despite the rich diversity, there are still many unidentified species to be regarded as new species within the genus (Plum and George 2009;Back and Lee 2014). According to Plum and George (2009), most of the species of Emertonia are discovered in the interstitial and coastal zone with an exception to four species found from the deep sea, E. andeep (Veit-Köhler, 2004), E. diva (Veit-Köhler, 2005), E. minor (Vasconcelos, Veit-Köhler, Drewes & Parreira dos Santos, 2009), and E. schminkei . Kunz (1962) divided the family Paramesochridae into nine genera based on the segmentation, and setae formula of swimming legs. Although Kunz (1962) proposed the name Kliopsyllus with the generic diagnosis based on four species (Leptopsyllus coelebs Monard, 1928; Paramesochra holsatica Klie, 1929;L. constrictus Nicholls, 1935, andP. major Nicholls, 1939) and two sub-species (P. holsatica varians Kunz, 1951, andP. constricata orotavae Noodt, 1958), he failed to fix the type species for the genus. Huys (2009) claimed that Emertonia Wilson, 1932 is the replacement name for Kliopsyllus. To date, 48 species including six sub-species have been reported in Emertonia, and most species are found from sandy sediments.
In Korea, taxonomic studies on coastal benthic copepods are underway. Song et al. (2012) summarized the marine and brackish-water harpacticoids found in Korea. They reported a list including 88 marine and brackish-water harpacticoids belonging to 23 families (Song et al. 2012). Especially in the case of the family Paramesochridae, 11 species are found in the coastal sandy sediments (Back and Lee 2014;Back and Lee 2017). As a part of ongoing taxonomical study on the harpacticoid copepods, we aim to describe two new species of Emertonia sampled from sandy beaches in Korean Waters.

Materials and methods
The sediment samples for Emertonia koreana sp. n. were collected from the Chulripo Beach in the west coast of the Korean peninsula. The sediment samples for E. simplex sp. n. were collected from a subtidal zone of Jeju Island. Samples were fixed with 5% buffered formalin and dissected specimens were mounted on several slides separately using lactophenol as mounting medium. Slides were sealed with transparent nail varnish. Observations of the specimens were carried out using an LEICA DM 6000 equipped with a drawing tube. Specimens were deposited in the Marine Biodiversity Institute of Korea (MABIK).
To prepare specimens for scanning electron microscope analysis (SU3500; Hitachi, in National Marine Biodiversity Institute of Korea), specimens were transferred to 100 % ethanol, dehydrated by t-BuOH freeze dryer (VFD-21S; Vacuum Device), mounted on stubs using double-sided tape, coated with gold-palladium, and then photographed.
The descriptive terminology was adopted from Huys et al. (1996). Abbreviations used in the text are:  Fig. 2A 3 ) consisting of short aesthetasc fused basally to two naked setae. Antenna (Fig. 2B). Four-segmented, comprising coxa, basis, one-segmented exp, and two-segmented enp; coxa small and bare; basis without any surface ornamentation; exp unequal Y-shape with one bare and one uni-pinnate setae; enp-1 with one bare abexopodal seta; enp-2 armed with one pinnate spine, two spine-like setae laterally, four geniculate setae around distal margin, and one longest geniculate seta fused at base with one bare seta.
Maxillule (Fig. 2D). Praecoxal arthrite well developed, with seven spines, two bare setae around distal margin, and two juxtaposed slender setae on anterior surface near outer margin; coxa fused with cylindrical endite, armed with two bare setae and one stout spine; basis fused with endite, armed with seven bare setae; exp one-segmented, small, with one bare and one pinnate setae; enp one-segmented, with five bare setae.
Maxilla (Fig. 2E). Syncoxa with three endites; proximal and second endites with one pinnate seta; third endite with one bare and two uni-pinnate setae; allobasis with one strong pinnate claw and two bare setae; enp one-segmented, with one stout spine and four bare setae.
P2, P3 (Fig. 3B, C). Coxa ornamented with rows of spinules; basis with one bare outer seta, one pore near base of exp, and rows of spinules as figured; exp three-segmented; exp-1 with one outer spine and ornamented with row of long spinules along inner margin; exp-2 with one outer spine, inner distal corner forming spinous projection; exp-3 with two outer spines and two pinnate setae; enp one-segmented, with one plumose apical seta.
P4 (Fig. 3D). Coxa ornamented with two rows of spinules on anterior surface; basis with one bare outer seta and one pore; exp three-segmented; exp-1 and exp-2 with one outer spine; exp-3 with one outer spines and one pinnate apical seta; enp one-segmented with one apical seta.   (Figs 1C, 5B). Comprising medially fused benps and discrete exps; benp with one basal seta and ornamented with one pore; endopodal lobes elongated and separated by median cleft; each with two pinnate modified setae; exopod with two pinnate and one modified setae, and outer corner forming projection.
Etymology. The species name refers the type locality of new species, Republic of Korea.
Remarks. The new species Emertonia koreana sp. n. is closely related with E. acutifurcata (Mielke, 1985). They share similar shape of caudal ramus. E. koreana sp. n. and E. acutifurcata only have sub-triangular caudal ramus. Within the genus Paramesochra, similar morphology of caudal ramus is observed in P. acutata acutata Klie, 1935, P. acutata hawaiiensis Kunz, 1981, and P. taeana Back & Lee, 2010. They also have same setal formula of P1-P5. E. koreana sp. n. can be easily distinguished from those species based on the following unique characteristics: 1) female P5 is deeply divided into two parts in the center of both P5 baseoendopods. 2) Two setae at the end of baseoendopod are swollen near the base. In addition, the base of the innermost seta of P5 exopods is swollen, similar to setae of baseoendopod. 3) There are rectangular frills, except for the last two segments of urosomite. This structure is similar to that of P. taeana, but has not been reported in the genus Emertonia yet.  Material examined. Holotype 1♀ dissected on 7 slides (MABIK CR00241575), and paratypes: 1♂ on 5 slides (MABIK CR00241576). Additional paratypes represented by 3 ♀♀ (MABIK CR00241577 ~ CR00241579) and 2 ♂♂ (MABIK CR00241580, CR00241581) in 70 % ethanol. 2♀♀ dried, mounted on stub, and coated with gold-palladium for SEM. All samples were collected from the type locality by J. Back on 4 June 2010.
Diagnosis. Emertonia simplex sp. n. with four setae at P5 exopod in male, and one short Inner seta at P5 baseoendopod in female. Caudal rami rectangular, approximately 3.8 times as long as its width. Body armed with long dorsal sensilla.
Caudal rami (Figs 9A, 11F). Rectangular, approximately 3.2 times as long as wide; with seven setae; setae III-VI located around distal margin of ramus; seta I small, bare, arising laterally; seta II bare; seta III cylindrical, bare; seta IV well developed, bare, seta V longest, pinnate in middle; seta VI bare; dorsal seta VII bi-articulate at base, bipinnate in middle.
Rostrum ( Fig. 6A) small, with rounded tip, fused with cephalothorax; without sensilla. Antennule ( Fig. 6C) slender, eight-segmented; proximal segment with row of long spinules along anterior margin and blunt process on lateral margin; fourth segment with sub-cylindrical process bearing one bare seta fused basally to aesthetasc; fifth segment with sub-cylindrical process with one bare seta (   Antenna (Fig. 7A). Coxa and basis without surface ornamentation; exp onesegmented, with two pinnate and three bare setae, and one spinule near outer distal corner; enp two-segmented; enp-1 with one pinnate seta, without surface ornamentation; lateral armature of enp-2 consisting of two bare setae, one pinnate seta, and long spinules along outer margin; distal armature of enp-2 (Fig. 7A 1 ) consisting of six geniculate and one bare setae (one long bare seta fused at base to largest geniculate seta).
Maxillule (Fig. 7C). Praecoxa subquadrate, with two long spinules; arthrite well developed, with six strong spines and two bare lateral setae, and two juxtaposed setae on surface; coxa with fused endite and three bare setae; basis fused with endites, with six setae; exp one-segmented, with one pinnate and one bare setae, and ornamented with row of spinules along inner margin; enp one-segmented, longer than exopod, with five bare setae around distal margin and one pore sub-distally.
Maxilliped (Figs 7E, 11C) four-segmented; syncoxa with one bare seta; basis and ornamented with row of spinules along outer margin; enp two-segmented; enp-1 with one small bare seta laterally and one stout claw on distal margin; enp-2 with two geniculate setae. P1 (Fig. 8A). Coxa and basis with spinules as figured; the latter with one bare outer and one bare inner setae; exp two-segmented; exp-1 longer than exp-2, the former with row of spinules along outer margin and one uni-pinnate outer spine; exp-2 with two uni-pinnate and two bare setae; enp approximately 1.8 times as long as exp; enp-1 elongate, bare, approximately five times as long as enp-2; enp-2 small, slightly longer than wide, with two claw-like setae.
P2, P3 (Figs 8B, C, 11D). Coxa with row of spinules on outer distal corner; basis with one bare outer seta, one pore near base of outer seta; exp three-segmented; exp-1 and exp-2 with one uni-pinnate spine; exp-3 with two uni-pinnate outer spines, one stout apical seta, and one pinnate seta; enp one-segmented with one pinnate apical seta.
P4 (Fig. 8D). Coxa ornamented with one row of spinules on outer distal corner; basis with one bare outer seta, one pore near base of outer seta; exp three-segmented; exp-1 and exp-2 with one uni-pinnate outer spine; exp-3 with one uni-pinnate outer spine and one apical seta; enp one-segmented, with one modified seta.  P5 (Figs 9B, 11E) with medially fused benps and discrete exps; benp with one pinnate outer basal seta; endopodal lobes well-developed, rounded, median cleft reaching at distal margin of exp, with one shorter inner and one longer outer setae; exp well developed, with one pinnate outer seta and two bare inner setae, and ornamented with a row of long spinules along inner margin.
Etymology. The species name refers to the simple somites without hyaline frills forming quadrilateral lappets.
Remarks. The second new species, Emertonia simplex sp. n., shares the general characteristics of other species like E. holsatica holsatica (Klie, 1929) and E. major (Nicholls, 1939), including segmentation and setal formula of swimming legs, rectangular caudal rami, and a well-developed P5 baseoendopod and separated exopod. However, E. simplex sp. n. has a combination of all the following characteristics: 1) exopod of antenna has five setae. This characteristic is found in eleven species of Emertonia, for instance E. regulexstans (Mielke, 1984b), and E. diva (Veit-Köhler, 2005), and 2) Two claw-like setae are present on the second segment of P1, which can be found in E. brevicaudata (Kornev and Chertoprud, 2008), E. californica (Kunz, 1981), E. insularis (Kunz, 1981), E. holsatica s. str., E. longifurcata (Scheibel, 1975), and E. unguiseta (Mielke, 1984). Of these, E. unguiseta is the species closest to E. simplex sp. n. since they share all of the characteristics mentioned above. However, differences between E. simplex sp. n. and E. unguiseta are as follows: 1) E. simplex sp. n. has four setae at P5 exopod in male, whereas E. unguiseta bears only three setae, 2) the new species has a shorter inner seta at P5 baseoendopod in female, whereas   E. unguiseta bears two subequal setae, 3) the length of caudal rami is approximately 3.8 times as long as its width, whereas that of E. unguiseta is 3.2 times of the width. In addition, the new species has long dorsal sensilla. The major morphological characteristics of the genus Emertonia, including the two new species were summarized in Table 1.
Discussion. The family Paramesochridae is divided into nine genera based on segmentation, and setal formula of swimming legs. Two new species clearly belongs to the genus Emertonia, because of: 1) one-segmented endopods of P2-P4 with one seta each, 2) three-segmented exopods of P2-P4, and 3) the one-segmented exopod of antenna. Kunz (1981) compared the width:length ratio of the caudal rami, the characteristics of caudal setae, and the number of setae on antenna, P4, and P5. Wells (2007) also considered the characteristics of caudal seta III, and the setae on P5, and the number and position of setae in antenna for identifying species of Emertonia. Table 1.

Species list and morphological comparison of the species in genus Emertonia
Wilson, 1932 based on female.  Chappuis (1954) described P5 benp with two setae, however we doubt he described a different species instead of E. constricta constricta.
In contrast to description of Nicholls (1935) and Marinov (1971), Chappuis (1954) described that the innermost seta of P5 exp is the longest among three setae.
3 Galhano (1970) described exp of A2 with two setae in the manuscript but with three in the figure.
6 Krishnaswamy (1957) illustrated the habitus with very small caudal ramus. It is very difficult to calculate the ratio of width:length. 7 The characters of E. masryi (Bodin, 1979) were based on Kliopsyllus minutus in Masry (1970).
A taxonomic key for the worldwide species of Emertonia is constructed as follows. Unfortunately, E. pontica (Serban, 1959) is excluded from the key due to incomplete original description (Serban, 1959;Wells, 2007)