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Research Article
Two new species of the genus Emertonia Wilson, 1932 from Korean waters (Copepoda, Harpacticoida, Paramesochridae)
expand article infoJinwook Back, Wonchoel Lee§
‡ National Marine Biodiversity Institute of Korea, Seocheon, Korea, South
§ College of Natural Sciences, Hanyang University, Seoul, Korea, South
Open Access

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.

Keywords

Crustacea, Jeju Island, Kliopsyllus, Taxonomy, Yellow Sea

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 (Veit-Köhler & Drewes, 2009).

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, and P. major Nicholls, 1939) and two sub-species (P. holsatica varians Kunz, 1951, and P. 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:

A1 antennule;

A2 antenna;

ae aesthetasc;

exp exopod;

enp endopod;

exp (enp)-1 (2, 3) to denote the proximal (middle, distal) segment;

P1–P6 first to sixth thoracopod;

benp baseoendopod.

Systematics

Order Harpacticoida Dana, 1846

Family Paramesochridae Lang, 1944

Genus Emertonia Wilson, 1932

Emertonia koreana sp. n.

Figs 1, 2, 3, 4, 5

Type locality

The Chulripo Beach, intertidal zone in the west coast of Korea, Yellow Sea (36°48'11.46"N, 126°08'58"E) by sand rinsing collected by J. Back on 14 May 2010 (Back and Lee 2014, as Emertonia sp. 3)

Material examined

Holotype 1♀ dissected on 4 slides (MABIK CR00241565). Paratypes: 1♂ on 3 slides (MABIK CR00241566), and 5 ♀♀ (MABIK CR00241570 – 00241574), 3 ♂♂ (MABIK CR00241567 – CR00241569) in 70 % ethanol. 1♀ and 1♂ dried, mounted on stub, and coated with gold-palladium for SEM.

Diagnosis

Female P5 deeply divided into two parts in the center of both P5 baseoendopods. Two setae of baseoendopod swollen near the base. Innermost seta of P5 exopods somewhat swollen at base, similar to setae of baseoendopod. Urosomites armed with rectangular frills, except for the last two segments.

Description of female

Body. Length 330 µm (n = 6, mean = 325 µm); largest width measured at cephalic shield; 55 µm; cylindrical, slightly depressed dorsoventrally; whole body very hyaline; sensilla and pores on dorsal surface as figured (Fig. 1A, B).

Prosome (Fig. 1A, B). Comprising cephalothorax, and three free pedigerous somites; cephalothorax bell-shaped, with sensilla and pores as figured; pleural areas weakly developed and posterolateral angles rounded; posterior margin smooth; somites bearing P2–P4 with strongly developed hyaline frills forming quadrilateral lappets (Fig. 1A–C).

Urosome (Fig. 1A–C) Genital somite and first abdominal somite completely fused forming genital double-somite; genital field located mid-ventrally at approximately half length of genital double-somite; copulatory pore presumably covered by P6; P6 (Figs 1C, 5C) represented by one plate with one uni-pinnate seta each side; penultimate somite with bilobed, smooth pseudoperculum; anal somite small, with two pores dorsally.

Caudal ramus (Figs 1D, E, 5A). Juxtaposed, approximately 2.8 times as long as greatest width, conical, distal margin acutely pointed; each ramus armed with seven setae; seta I small, bare, arising ventrally; seta II bare; setae III stout, ornamented with spinule-like elements; seta IV bare; seta V pinnate, longest; seta VI shortest, bare; setae IV–VII displaced onto dorsal surface of ramus; seta VII bi-articulate at base and arising from inner dorsal surface.

Rostrum (Fig. 1A). Triangular, ventrally directed, fused with cephalic shield, without sensilla.

Figure 1. 

Emertonia koreana sp. n., holotype (♀). A habitus, dorsal B habitus lateral C urosome, ventral D caudal rami, dorsal E caudal seta IV and V. Scale bars are in µm.

Antennule (Fig. 2A). Eight-segmented; proximal segment longest and ornamented with a few long spinules along lateral margin; fourth segment (Fig. 2A1) forming sub-cylindrical process armed with one long slender seta fused basally to aesthetasc; sixth segment (Fig. 2A2) armed with one slender bare seta arising from ventral sub-cylindrical process; armature formula: 1 – [1 bare], 2 – [5 bare + 3 pinnate], 3 – [6 bare + 1 pinnate], 4 – [2 bare + 1 pinnate + (1 + ae)], 5 – [1 bare], 6 – [3 bare], 7 – [3 bare], 8 – [6 bare + acrothek]; apical acrothek (Fig. 2A3) 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.

Mandible (Fig. 2C). Coxa with gnathobase bearing one bare seta at dorsal corner and seven teeth; palp (Fig. 2C1) biramous, comprising basis, one-segmented exp and two-segmented enp; basis widening distally, with one pinnate seta; exp with two lateral and two distal setae; enp-1 with two bare setae; enp-2 with five basally fused setae at apex.

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.

Maxilliped (Fig. 2F) four-segmented, comprising syncoxa, basis and two-segmented enp; syncoxa with one bare seta distally; basis bare; enp-1 with one geniculate and one small setae; enp-2 small, with two geniculate and one bare setae around distal margin.

Figure 2. 

Emertonia koreana sp. n., holotype (♀). A antennule (A1 fourth segment A2 fifth, sixth, and seventh segments A3 last segment) B antenna C mandible (C1 plap) D maxillule E maxilla F maxilliped. Scale bar is in µm

P1 (Fig. 3A). Coxa ornamented with rows of spinules; basis with one pinnate inner seta and one bare outer seta, and ornamented with one pore near base of outer seta; enp 1.9 times as long as exp; exp two-segmented; exp-1 with one pinnate outer seta; exp-2 short, sub-quadrilateral, with three pinnate and one uni-pinnate setae; enp two-segmented; enp-1 long, bare; enp-2 small, with two short geniculate 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.

Figure 3. 

Emertonia koreana sp. n., holotype (♀). A P1 B P2 C P3 D P4. Scale bar is in µm.

Armature formula as follows:

Exopod Endopod
P1 0.121 0.011
P2 0.0.112 010
P3 0.0.112 010
P4 0.0.011 010

P5 (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.

Description of male

Body (Fig. 4A) length 320 µm (n = 4, mean = 315 µm); largest width measured at posterior margin of cephalic shield: 45 µm; general body shape and ornamentation as in female; except for last two urosomites, urosome somites present strongly developed hyaline frills from dorsal to venteral (Fig. 5D); additional sexual dimorphism in A1, P5, and P6.

Antennule (Fig. 4B). Seven-segmented, short, robust, subchirocer; fifth-segment (Fig. 4B1) swollen, largest, forming sub-cylindrical process with one long slender seta fused basally to aesthetasc. Armature formula: 1 – [1 bare], 2 – [7 bare + 1 pinnate], 3 – [2 bare + 1 pinnate], 4 – [2 bare], 5 – [3 bare + 2 pinnate + (1 + ae)], 6 – [2 bare], 7 – [5 bare + acrothek], acrothek (Fig. 4B2) consisting of aesthetasc and two bare setae.

Figure 4. 

Emertonia koreana sp. n., (♂). A habitus, dorsal B antennule (B1 fifth segment B2 last segment) C P5 D P6. Scale bars are in µm.

legs P1–P4 shape and setae formulae as in female (Fig. 5E, F)

P5 (Figs 4C, 5G). Comprising medially fused benp and discrete exp; benp with one basal seta; endopodal lobes weakly developed, without any element; exopod small, with two pinnate outer and one modified inner setae.

P6 (Figs 4D, 5H). Asymmetrical; each P6 with one outer and two inner setae, ornamented with one pore.

Figure 5. 

Emertonia koreana sp. n., SEM photographs. A caudal rami, ventral (♀) B P5 (♀) C P6 (♀) D sixth and seventh somites, ventral (♂) E P1 (♂) F P2 and P3 (♂) G P5 (♂) H P6 (♂).

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.

Emertonia simplex sp. n.

Figs 6, 7, 8, 9, 10, 11

Type locality

A subtidal zone near the Seogwipo Port in Jeju Island, Korea (33°13'33"N, 126°34'39"E), and sampled by using a grab (surface area: 0.1 m2) on a fishing boat (Back and Lee 2014, as Emertonia sp. 2), depth 15–20 m, sand.

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.

Description of female

Body cylindrical, slightly depressed dorsoventrally (Figs 6A–B, 11A), with long sensilla (Fig. 11B); total body length, 390 µm (n = 7, mean = 376 µm); largest width (85 µm) measured at posterior margin of cephalic shield; body somites without hyaline frills forming quadrilateral lappets.

Prosome (Fig. 6A, B). Comprising cephalothorax, and three free pedigerous somites; Cephalothorax bell-shaped, with several sensilla; pleural areas weakly developed, posterolateral angles rounded.

Urosomites (Fig. 6A, B). Gradually tapering posteriorly; genital somite and third urosomite completely fused forming genital double-somite (Figs 9C, 11E); genital field located in proximal half of genital double-somite, with copulatory pore positioned medially, and two pores; P6 (Figs 9C, 11E) represented by narrow transverse plate, each side armed with one pinnate seta; anal somite (Fig. 9A) without anal operculum, but with rounded pseudoperculum arising from penultimate somite.

Figure 6. 

Emertonia simplex sp. n., (♀) A habitus, dorsal B habitus, lateral C antennule (C1 fifth, sixth, and seventh segments C2 last segment). Scale bars are in µm.

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 (Fig. 6C1); armature formula: 1 – [1], 2 – [7 bare + 1 spinulose], 3 – [6 bare], 4 – [2 bare + (1 + ae)], 5 – [1 bare], 6 – [2 bare], 7 – [4 bare], 8 – [5 bare + (2 + ae)]; apical acrothek consisting of one apical aesthetasc and two basally fused bare setae (Fig. 6C2).

Antenna (Fig. 7A). Coxa and basis without surface ornamentation; exp one-segmented, 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. 7A1) consisting of six geniculate and one bare setae (one long bare seta fused at base to largest geniculate seta).

Mandible (Fig. 7B). Coxa well developed; gnathobase with seven blunt teeth and one small pinnate seta at dorsal corner; palp biramous (Fig. 7B1), basis elongate, with two bare setae; exp one-segmented, with one pinnate and three bare setae; enp two-segmented, enp-1 1.7 times as long as enp-2, enp-1 with two bare setae; enp-2 with five setae fused at base.

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.

Maxilla (Fig. 7D). Syncoxa armed with three endites; first endite (Fig. 7D1) bilobed, with one pinnate and two bare setae; second endite (Fig. 7D2) with one pinnate seta and one bare setae; distal endite with two pinnate and one bare setae; allobasis with two uni-pinnate stout setae on distal margin; enp two-segmented; enp-1 rectangular, with one pinnate seta near base, two bare and one pinnate setae; enp-2 with one pinnate and two bare setae along distal margin.

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.

Figure 7. 

Emertonia simplex sp. n., (♀). A antenna (A1 end of second segment in antenna endopod) B mandible (B1 palp) C maxillule D maxilla (D1 first endite D2 second endite D3 first segment of endopod D4 second segment of endopod) E maxilliped. Scale bar is in µm.

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.

Figure 8. 

Emertonia simplex sp. n., (♀). A P1 B P2 C P3 D P4. Scale bar is in µm.

Armature formula as follows:

Exopod Endopod
P1 0.121 0.011
P2 0.0.112 010
P3 0.0.112 010
P4 0.0.011 010

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.

Figure 9. 

Emertonia simplex sp. n., (♀). A last two segments of urosomite and caudal rami B P5 C P6 and genital field. Scale bars are in µm.

Description of male

Smaller than female, body length 345 µm (n = 3, mean = 344 µm) (Fig. 10A); largest width (80 µm) measured at posterior margin of cephalic shield; general body shape and ornamentation as in female except for separation of genital somite; additional sexual dimorphism in antennule, A1, P5, and P6.

Antennule (Fig. 10B). Seven-segmented, subchirocer; fifth segment (Fig. 10B2) swollen, largest; aesthetascs on fifth and seventh segments (Fig. 10B1); armature formula: 1 – [1 bare], 2 – [8 bare], 3 [5 –bare], 4 – [2 bare], 5 – [6 bare + 2 spinulose + (1 +ae)], 6 – [2 bare], 7 – [7 bare + (2 + ae)]; apical acrothek consisting of apical aesthetasc and two basally fused bare setae.

P5 (Fig. 10C). Benp confluent, forming large transverse plate, with one bare outer basal seta and one pore on either side; exp ovate bearing setules on inner margin, with two pinnate and two bare setae, innermost longest.

P6 (Fig. 10D). Clearly distinct medially, each P6 with one outer pinnate and two bare inner setae.

Figure 10. 

Emertonia simplex sp. n., (♂). A habitus, dorsal B antennule (B1 last two segments B2 fifth segment) C P5 D P6. Scale bars are in µm.

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.

Species list and morphological comparison of the species in genus Emertonia Wilson, 1932 based on female.

Species A1 A2 P1 P2 P3 P4 P5 Caudal rami
number of seg. exp setae exp-1 exp-2 enp-2 exp-2 exp-3 exp-2 exp-3 enp-1 exp-2 exp-3 enp-1 enp-2 exp benp shape
setae setae width:lenth
gracilis-group
E. gracilis Wilson, 1932 8 3 023 · 011 0 011 0 011 010 0 011 010 3 2 square
1:2
E. pseudogracilis Krishnaswamy, 1957 7 2 122 · 011 0 012 0 012 010 0 011 010 3 1 square
1:2.5
laurentica-group
E. laurentica (Nicholls, 1939) 7 ? 0 121 011 221 · 221 · 010 112 · 010 3 2 square
1:2
andeep-group
E. andeep (Veit-Köhler, 2004) 8 5 0 121 011 0 112 0 112 110 0 011 1 011 3 2 square
1:4
E. minor (Vasconcelos, Veit-Köhler, Drewes & Parreira dos Santos, 2009) 7 4 0 121 011 0 112 0 112 010 0 011 0 010 ? ? square
1:5
coelebs-group
E. coelebs (Monard, 1935) 7 4 0 121 011 0 112 0 112 010 1 011 110 · 3 ?1 square
1:5
E. psammophila (Noodt, 1964) 8 3 0 121 011 0 112 0 112 010 1 011 010 · 3 2 square
1:2.5
E. furcavaricata Kunz, 1974 8 ? 0 121 011 1 112 1 112 010 1 011 010 · 3 2 square
1:2.5
E. atlantica (Kunz, 1983) 7 3 0 121 011 0 112 0 112 010 1 011 110 · 3 1 square
1:3
holsatica-group
E. holsatica holsatica (Klie, 1929) 7 4(5)2 0 121 011 0 112 0 112 010 0 011 010 · 3 2 square
1:2
E. holsatica varians (Kunz, 1951) 7 5 0 121 011 0 112 0 112 010 0 011 110 · 3 2 square
1:3.5
E. holsatica longicaudata (Galhano, 1970) 7 2(3)3 0 121 011 0 112 0 112 010 0 011 010 · 3 2 square
1:3.5
E. constricta constricta (Nicholls, 1935) 7 2(1)4 0 121 011 0 012 0 012 010 0 012 (011)4 010 · 3 ? square
1:3
E. constricta orotavae (Noodt, 1958) 7 2(3)5 0 121 011 0 012 0 012 010 0 011 010 · 3 2 square
1:2
E. constricta pacifica (Mielke, 1984a) 8 4 0 121 011 0 012 0 012 010 0 011 010 · 3 2 square
1:3
E. constricta egyptica (Mittwally & Montagna, 2001) 8 4 0 121 011 0 012 0 012 010 0 011 010 · 3 2 square
1:4
E. major (Nicholls, 1939) 9 3 0 121 011 0 112 0 012 010 0 011 010 · 3 2 square
1:3
E. pygmaea (Nicholls, 1939) 7 3 0 121 011 0 112 0 112 010 0 011 010 · 5 2 square
1:2
E. longisetosa (Krishnaswamy, 1951) 7 2 0 121 011 0 112 0 112 010 0 011 010 · 3 2 square
1:3
E. arenicola (Krishnaswamy, 1957) 7 2 0 121 011 0 112 0 112 010 0 011 010 · 3 2 square
1:3
E. capensis Krishnaswamy, 1957 7 1 0 121 011 0 012 0 012 010 0 011 010 · 3 0 square
1:2
E. minuta Krishnaswamy, 1957 7 3 0 122 011 0 012 0 012 010 0 011 010 · 3 0 square
1:2
E. enalia (Krishnaswamy, 1957) 8 1 0 022 011 0 112 0 112 010 0 011 010 · 3 2 square
1:4(?)6
E. wilsoni (Krishnaswamy, 1957) 7 3 0 121 011 0 112 0 112 010 0 011 010 · 3 2 square
1:3
E. pontica (Serban, 1959) 9 3 ? ? ? ? ? ? ? ? ? ? ? · 3 2 square
1:3.5
E. perharidiensis (Wells, 1963) 7 4 0 121 011 0 112 0 012 010 0 011 110 · 3 2 square
1:5
E. psammobionta (Noodt, 1964) 7 3 0 121 011 0 112 0 112 010 0 011 010 · 3(2) ? square
1:2
E. idiotes (Wells, 1967) 6 3 0 121 011 0 112 0 112 010 0 111 010 · 3 2 square
1:2.5
E. paraholsatica (Mielke, 1975) 7 4 0 121 011 0 112 0 112 010 0 011 010 · 3 2 square
1:3
E. longifurcata (Scheibel, 1975) 7 4 0 121 011 0 112 0 112 010 0 011 010 · 3 2 square
1:2.5
E. spiniger spiniger (Wells, Kunz & Rao, 1975) 7 5 0 022 020 0 112 0 112 010 0 011 110 · 3 2 square
1:6.5
E. spiniger ornata (Kunz, 1981) 7 5 0 022 020 0 112 0 112 010 0 011 110 · 3 2 square
1:9
E. masryi (Bodin, 1979)7 8 2 0 121 011 0 012 0 012 010 0 011 010 · 3 3 square
1:2
E. californica (Kunz, 1981) 7 3 0 121 011 0 112 0 112 010 0 020 010 · 3 2 square
1:3
E. debilis (Kunz, 1981) 8 3 0 121 011 0 112 0 112 010 0 011 010 · 3 2 square
1:2
E. insularis (Kunz, 1981) 8 4 0 121 011 0 112 0 112 010 0 011 010 · 3 2 square
1:3
E. miguelensis (Kunz,1983) ? 3 0 121 011 0 112 0 112 010 0 011 010 · ? ? square
1:3.5
E. panamensis (Mielke, 1984a) 8 2 0 121 011 0 112 0 112 010 0 111 010 · 3 1 square
1:2
E. regulexstans (Mielke, 1984b) 8 5 0 121 011 0 112 0 112 010 0 011 010 · 3 2 square
1:2.3
E. similis (Mielke, 1984b) 8 5 0 121 011 0 112 0 112 010 0 011 010 · 3 2 square
1:3
E. unguiseta (Mielke, 1984b) 8 5 0 121 011 0 112 0 112 010 0 011 010 · 3 2 square
1:3.2
E. acutifurcata (Mielke, 1985) ? 4 0 121 011 0 112 0 112 010 0 011 010 · 3 2 subtriangular
1:4
E. chilensis (Mielke, 1985) 8 4 0 121 011 0 112 0 112 010 0 011 010 · 3 2 square
1:2
E. diva (Veit-Köhler, 2005) 8 5 0 121 011 0 112 0 112 010 0 011 011 · 3 2 square
1:5.5
E. brevicaudata (Kornev & Chertoprud, 2008) 7 4 0 121 011 0 112 0 112 010 0 011 010 · 3 2 square
1:1.6
E. schminkei (Veit-Köhler & Drewes 2009). 8 5 0 121 011 0 112 0 112 010 0 011 010 · 3 2 square
1:9
E. clausi Pointner & Veit-Köhler, 2013 7 5(6)8 0 121 010 0 112 0 112 010 0 011 010 · 3 2 square
1:5.5
E. ingridae Pointner & Veit-Köhler, 2013 8 5 0 121 010 0 112 0 112 010 0 011 010 · 3 2 square
1:4.5
E. koreana sp. n. (This study) 8 2 0 121 011 0 112 0 112 010 0 011 010 · 3 2 subtriangular
1:3
E. simplex sp. n. (This study) 8 5 0 121 011 0 112 0 112 010 0 011 010 · 3 2 square
1:3.8

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.

Kunz (1981) and Huys (1987) proposed the phylogenetic position of the genera within the Paramesochridae. Kunz (1981) mentioned the diagnosis of Kliopsyllus based on the segmentation, and the seta formula of appendages. However, some species do not fit to the diagnosis by Kunz (1981). According to Huys’ (1987) cladogram of Paramesochridae, three genera in the Paramesochra-group are divided by six apomorphies: 1) four setae on distal segment of P1 exopod, 2) one-segemented endopod of P2–P4, 3) three setae on the distal segment of P4 exopod, 4) one-segmented exopod of P1, 5) P1 endopod without element, and 6) two setae on distal segment of P4 exopod and one seta on P4 endopod. However, some species of Emertonia do not fit to Huys’ cladogram as well. For example, E. andeep (Veit-Köhler, 2004) and E. minor (Vasconcelos, Veit-Köhler, Drewes & Parreira dos Santos, 2009) have two-segmented endopod of P4, E. idiotes (Wells, 1967) has three setae on P4 exp-3, and E. gracilis Wilson, 1932 and E. pseudogracilis Krishnaswamy, 1957 have one-segmented exopod of P1 (Table 1). Therefore the diagnosis of Emertonia needs to be amended as follows:

Amended diagnosis

Paramesochridae. Body cylindrical, broad anteriorly, rather flattened; with distinct separation between prosome and urosome; rostrum small, fused at base. Operculum not developed. Caudal ramus with 6 or 7 setae, seta I small or obscure. Antennule 7- or 8-segmented in female. Antennary exopod 1-segmented with 1–5 setae. Mandible biramous; exopod 1-segmented with 2–4 setae; distal segment of endopod with several basally fused setae at apex. Maxilla with 3 endites on syncoxa, first endite bilobed; endopod 1- or 2-segmented. Maxilliped with elongate basis. P1 biramous, with 2-segmented endopod and 1-or 2-segmented exopod. P2–P3 biramous, with 2- or 3-segmented exopods and 1-segmented endopods; P4 biramous, with 1- or 2-segmented endopod and 2- or 3-segmented exopod.

Five distinctive groups within genus Emertonia can be recognized based on segmentation and setal formula in swimming legs: 1) gracilis-group, 1-segmented exopod of P1; 2) laurentica-group, 2-segmented exopod of P2–P4; 3) andeep-group, 2-segmented endopod of P4; 4) coelebs-group, P4 exp-2 with one inner seta; 5) holsatica-group, 2-segmented exopod of P1, 3-segmented exopod of P2–P4, 1-segmented endopod of P2–P4, and P2–P4 exp-2 without inner seta. However, more studies including the mouthparts, and the numbers and shapes of elements on the appendages will be necessary to confirm the phylogenetic relationships among the species of Emertonia.

Figure 11. 

Emertonia simplex sp. n. (♀), SEM photographs. A habitus, lateral B first and second segment, lateral C P1 D P3 C P3 E P5 F caudal rami, lateral.

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)

1 P1 exopod 1-segmented…(gracilis-group) 2
P1–P4 exopod 2-segmented…(laurentica-group) E. laurentica
P1 exopod 2-segmented , P4 endopod 2-segmented…(andeep-group) 3
P1 exopod 2-segmented, P4 exopod 3-segmented; P4 exp-2 with 1 inner seta (coelebs-group) 4
Theses character not combined…(holsatica-group) 7
2 P2–P3 exp-3 with 2 setae/spines E. gracilis
P2–P3 exp-3 with 3 setae/spines E. pseudogracilis
3 P4 enp-2 with 2 setae E. andeep
P4 enp-2 with 1 seta E. minor
4 P2–P3 exp-2 with 1 inner seta E. furcavaricata
P2–P3 exp-2 without inner seta 5
5 Length of caudal rami 5 times as long as wide; P4 enp-1 with 2 setae E. coelebs
These characters not combined 6
6 P4 enp-1 with 1 seta; P4 baseoendopodal lobe with 2 setae E. psammophila
P4 enp-1 with 2 setae; P4 baseoendopodal lobe with 1 seta E. atlantica
7 P2 exp-3 with 3 setae/spines 8
P2 exp-3 with 4 setae/spines 14
8 P1 exp-2 with 5 setae/spines E. minuta
P1 exp-2 with 4 setae/spines 9
9 A2 exopod with 1 seta at most E. capensis
A2 exopod with 2 setae at least 10
10 A2 exopod with 2 setae and P5 baseoendopodal lobe with 3 setae E. masryi
These characters not combined…(E. constrictus s. str.) 11
11 A1 7-segmented and A2 exp with 3 setae at most 12
A1 8-segmented and A2 exp with 4 setae 13
12 P1 enp-1 length 1.6 times longer than P1 exp, length of caudal rami 3 times as long as wide E. constricta constricta
P1 enp-1 length 1.2 times longer than P1 exp, length of caudal rami 2 times as long as wide E. constricta orotavae
13 V-shaped baseoendopod of male P5 without setules E. constricta pacifica
Each side baseoendopodal lobe almost fused ornamented with row of setules E. constricta egyptica
14 P4 exp-3 with 3 setae 15
P4 exp-3 with 2 setae 16
15 A2 exp with 2 elements and P5 baseoendopod with 1 seta E. panamensis
A2 exp with 3 elements and P5 baseoendopod with 2 setae E. idiotes
16 P4 enp-1 with 2 setae 17
P4 enp-1 with 1 setae 21
17 P3 exp-3 with 3 setae E. perharidiensis
P3 exp-3 with 4 setae 18
18– Length of caudal rami more than 3.5 times as long as wide; penultimate somite normal E. holsatica varians
Length of caudal rami more than 5 times as long as wide 19
19 Penultimate somite normal; endopod of P4 with 2 pinnate setae E. diva
Penultimate somite elongated and ornamented 2 dorsal processes/spines; endopod of P4 with 1 bare and 1 brushlike setae 20
20 Length of caudal rami over 6–7 times as long as wide E. spiniger spiniger
Length of caudal rami over 9 times as long as wide E. spiniger ornata
21 P5 exopod with 5 setae E. pygmaea
P5 exopod with 3 setae 22
22 Shape of caudal rami conical, sub-triangular 23
Shape of caudal rami square 24
23 A2 exopod with 4 setae; median depression between baseoendopodal lobes shallow E. acutifurcata
A2 exopod with 2 setae; median depression between baseoendopodal lobes deeply E. koreana sp. n.
24 A2 exopod with 1 seta E. enalia
A2 exopod with at least 2 setae 25
25 A2 exopod with 2 setae 26
A2 exopod with 3 setae 28
A2 exopod with 4 setae 33
A2 exopod with 5 setae 38
26 Caudal rami with inwardly pointed spine and long seta V E. longisetosa
These characters not combined 27
27 End of P2–P3 enp globular; A2 exopod with 2 or 3 setae E. holsatica longicaudata
Shape of P2–P3 endopods normal; A2 exopod with 2 setae E. arenicola
28 Distal segment of P3 exopod with 3 setae E. major
Distal segment of P3 exopod with 4 setae 29
29 Seta V of caudal rami consisted of two type elements, proximal half stout and distal half slender seta E. miguelensis
Seta V of caudal rami normal 30
30 A1 8-segmented; P1 endopod 1.3 times longer than exopod; length of caudal rami twice as long as wide E. debilis
These characters not combined 31
31 A1 7-segmented; P2 and P3 endopod with a single tiny spinule-like seta each; length of caudal rami 3 times as long as wide E. wilsoni
These characters not combined 32
32 Baseoendopod of P5 with two apical setae; male exp of P5 with 3 setae E. californica
Baseoendopod of P5 with one apical and one outer setae; male exp of P5 with four setae E. psammobionta
33 Baseoendopodal lobes fused forming large plate; A1 8-segmented; male exp of P5 with four setae E. insularis
These characters not combined 34
34 A1 8-segmented; P1 enp-1 ornamented with long setules; length of P1 enp-1 1.6 times as long as P1 enp-2; male P5 exp with three setae E. chilensis
These characters not combined 35
35 Seta III of caudal rami blunt spine; apical seta of A2 exp stout comparison with other three setae; Caudal rami length approx. 2.5 times as long as wide E. longifurcata
These characters not combined 36
36 Maxilliped enp 2-segmented; Caudal rami length approx. 1.6 times as long as wide E. brevicaudata
These characters not combined 37
37 Caudal rami length approx. 2 times as long as wide; length of P1 enp-1 7 times as long as P1 enp-2 E. holsatica holsatica
Caudal rami length approx. 3 times as long as wide; length of P1 enp-1 approx. 2.7 times as long as P1 enp-2 E. paraholsatica
38 Baseoendopodal lobes fused forming large plate; P1 enp-1 and P1 exp equal in length E. regulexstans
These character not combined 39
39 Caudal rami length more than 5 times as long as wide 40
Caudal rami length under 5 times as long as wide 41
40 Caudal rami length 9 times as long as wide; P5 exp with 1 pinnate and 2 bare setae, outermost longest E. schminkei
Caudal rami length 5.5 times as long as wide; P5 exp with 3 bare setae, innermost longest E. clausi
41 P2–P3 enp apical seta length longer than enp 42
P2–P3 enp apical seta length shorter than enp 43
42 P1 enp-2 with 1 seta E. ingridae
P1 enp-2 with 2 setae/spine E. simplex sp. n.
43 Length of P1 enp-1 2.5 times as long as P1 exp; male P5 exp with 3 setae E. unguiseta
P1 enp-1 and P1 exp same length; male P5 exp with 4 setae E. similis

Acknowledgements

This research was supported by Evaluation of Marine Invertebrate Bioresources (MABIK 2017M00600) sponsored by the National Marine Biodiversity Institute of Korea. Authors express a hearty thanks to Raehyuk Jung (Hanyang University) for his help in English correction of the early version of manuscript. We are also very grateful to subject editor, Dr. Kai Horst George and the two reviewers, Dr. Elena Chertoprud, and Dr. Sung Joon Song, for their help in greatly improving this manuscript.

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