INTRODUCTION

The family Miraciidae Dana, 1846 is one of the most abundant and diverse group of harpacticoid copepods in marine sediments (De Troch et al. 2008). Among them, RobertgurneyaApostolov & Marinov, 1988 is one of the dominant genera, being composed of 17 species and subspecies, but so far, no species have been reported in East and Southeast Asia.

Gómez (2020) recognized 17 valid species and subspecies within the genus Robertgurneya in his revision [R. arabica (Noodt, 1964), R. brevipes (Wells & Rao, 1987), R. dactylifer (Wilson C.B., 1932), R. dictydiophora (Monard, 1924), R. diversa (Lang, 1965), R. ecaudata (Monard, 1936), R. falklandiensis (Lang, 1936), R. hopkinsi (Lang, 1965), R. ilievecensis (Monard, 1935), R. mexicanaGómez, 2020, R. oligochaeta (Noodt, 1955), R. remanei (Klie, 1950), R. similis bulbamphiascoides (Noodt, 1955), R. rostrata (Gurney, 1927), R. similis similis (Scott A., 1896), R. simulans (Norman & Scott T., 1905), and R. smithi (Hamond, 1973)].

Lang (1944) divided the genus into two species groups: the similis and the spinulosus groups, after that, Lang (1948) corrected the group name spinulosus to spinulosa. Gómez (2020) proposed a new genus Robertgurneyella Gómez, 2020 (type by monotypy: R. spinulosa (Sars G.O., 1911)), and he suggested changing the species group name from spinulosa to rostrata.

Currently, the similis group consists of R. brevipes, R. diversa, R. falklandiensis, R. hopkinsi, R. remanei, R. similis bulbamphiascoides, R. similis similis, R. simulans, and R. smithi. The rostrata group is composed R. arabica, R. dactylifer, R. dictydiophora, R. ecaudata, R. ilievecensis, R. mexicana, R. oligochaeta, and R. rostrata.

During a survey of the meiofauna along Korean coast, harpacticoid copepods have been collected. The new species is described and illustrated herein as Robertgurneya donghaensis sp. nov. from sediments of the East Sea of Korea.

MATERIALS AND METHODS

Sediment samples were obtained from Bong-gil Beach, Gyeongju, Korea (35°44ʹ21.1ʺN, 129°29ʹ03.0ʺE) in 8 January 2019. Samples were taken with a sediment core or a hand net, and fixed with 70% ethanol. Meiofauna were extracted from the sediments by the Ludox centrifugation method (Burgess 2001). Copepods were sorted under a Leica S APO stereo microscope, and were dissected in lactic acid, and the dissected appendages were permanently mounted on slides in lactophenol. All drawings were prepared using a differential interference contrast microscope (Leica DM2500; Leica Microsystems, Germany). Specimens were deposited at the National Institute of Biological Resources (NIBR) of Korea. The descriptive terminology is adopted from Huys et al. (1996). Abbreviations used in the text are: A1, antennule; A2, antenna; ae, aesthetasc; enp, endopod; exp, exopod; P1-P6, first to sixth thoracopod; exp (enp)-1 (2, 3) to denote the proximal (middle, distal) segment of a ramus. Scale bars in figures are indicated in μm.

SYSTEMATIC ACCOUNT

Order Harpacticoida Sars, 1903

Family Miraciidae Dana, 1846

Genus RobertgurneyaApostolov & Marinov, 1988

Robertgurneya donghaensis sp. nov. Fig. 1-10

Type locality. Bong-gil Beach, Gyeongju, Korea (35°44ʹ 21.1ʺN, 129°29ʹ03.0ʺE).

Material examined. Holotype 1♀ (ZCIVIV0000004258) dissected on 9 slides. Paratypes: 7♀♀ and 4♂♂; 2♀ ♀ (NIBRIV0000895283-4) on 18 slides, 2♂♂ (NIBRIV0000895285- 6) on 17 slides, 5 ♀♀ preserved in 70% ethanol (NIBRIV0000862785), and 2♂♂ (NIBRIV0000895282) in 70% ethanol, vial. All from the type locality, collected by H.W. Bang and H. Moon in January 2019.

Etymology. The species name refers to the type locality, “Donghae” means the East Sea in Korean.

Description. Female (holotype). Total body length 795 μm (n=5; range: 730-859 μm), measured from anterior margin of rostrum to posterior margin of caudal rami. Largest width measured at posterior margin of cephalic shield: 165 μm.

Habitus (Fig. 1A, B) moderately slender, fusiform. Urosome slightly narrower than prosome. Cephalothorax gradually tapering anteriorly, sensillar pattern on cephalothorax and body somites as figured. Rostrum (Fig. 4E) prominent, acuminate, with one sensilla arising medially on each side. Cephalothorax, second and third pedigerous somites with well-developed hyaline frills.

Urosome (Figs. 1 and 2A) five-segmented, comprising P5-bearing somite, genital double-somite and three free abdominal somites, slightly narrower than prosome, the second free abdominal somite with well-developed hyaline frill along the posterior margin (Fig. 2C)

Genital double-somite (Fig. 2A) completely fused, subdivided by chitinous suture dorsally and laterally, with sensilla and pores as shown. Anal somite (Fig. 2D) deeply cleft medially, without anal operculum, with a pair of small dorsal sensilla. Caudal ramus (Fig. 2D) as long as broad, with seven setae: seta I shortest; seta II pinnate; seta III bare; seta IV pinnate and long; V sparsely bipinnate, about 1.8 times as long as seta IV; seta VI bare; seta VII bi-articulate at base and pinnate.

Antennule (Fig. 3A) eight-segmented, all segments smooth, all seta naked, aesthetascs on segments 4 and 8. Segment 2 longest. Armature formula: 1-[1], 2-[11], 3-[6], 4-[5+(1+ae)], 5-[2], 6[4], 7-[4], 8-[5+acrothek]. Apical acrothek consisting of aesthetasc and two naked setae fused basally.

Antenna (Fig. 3B) three-segmented, comprising coxa, allobasis, free one-segmented enp and three-segmented exp. Coxa small. Allobasis with a pinnate abexopodal seta on median inner margin. Exopod three-segmented; exp-1 longer than exp-2 and exp-3 combined, with a long pinnate seta; exp-2 shortest without a seta; exp-3 with few spinules present around distal corner, with one lateral seta and two pinnate setae apically. Endopod slightly shorter than allobasis, with an inner strong spinules, and with spinules near posterior corner; armed with two lateral inner spines, one distal spine, three single geniculate setae, one short naked seta, and one strongly spinulose geniculate outer seta fused basally to slender bare seta.

Labrum (Fig. 3C) well developed, spinular ornamentation on anterior surface as in figure.

Mandible (Fig. 4A) with well-developed gnathobase bearing several strong multicuspidate teeth as figured. Palp well-developed, biramous. Basis with three plumose inner setae. Endopod one-segmented, with two lateral and six apical setae, of which two distal fused at base. Exopod two-segmented; exp-1 with one lateral and one distal spinulose seta; exp-2 small, with two bare and one plumose seta.

Maxillule (Fig. 4B). Praecoxal arthrite with seven strong spinulose distal spines, two pinnate lateral spines, and two setae on the anterior surface. Coxo-endite with one pinnate spine and one seta. Basis elongated, with one pinnate and four bare elements. Endopod one-segmented, with four smooth elements. Exopod one-segmented, with two pinnate setae.

Maxilla (Fig. 4C) comprising syncoxa, allobasis, and endopod. Syncoxa with two endites; proximal endite with two pinnate strong and one bare spine among distal margin; second endite with one strong spine. Allobasis drawn out into strong pinnate claw, with one strong pinnate spine, and one slender seta. Endopod one-segmented, with six setae.

Maxilliped (Fig. 4D) subchelate. Syncoxa with two pinnate setae distally. Basis elongated, with spinules along inner margin. Endopod elongated, bearing terminal claw plus one strong spine and one small seta.

Swimming legs 1-4 (Figs. 5A, B and 6A, B) jointed by intercoxal sclerite without ornamentation. Coxae and bases with surface ornamentations of spinules as figured. All swimming legs with three-segmented exopods and endopods.

P1 (Fig. 5A). Intercoxal sclerite rectangle. Coxa large, as long as wide, and with spinular rows on anterior surface. Basis with one outer and one inner strong pinnate spine, with strong spinules close to insertion of inner spines, and on medial apical rounded extension. Exopod three-segmented; exp-1 and exp-2 subequal in length, without inner seta; exp-3 with two outer spines and two distal geniculated setae. Enp-1 elongated, about 7.2 times longer than it is broad, and 2.2 times as long as second and third segments combined, with one inner seta; enp-2 with one inner plumose seta and with strong spinules distally on outer margins; enp-3 with stout spinules along outer margins, with one plumose inner seta, and one geniculated seta distally, and one well-developed unipinnate outer spine.

P2-P4 (Figs. 5B and 6A, B). Coxae ornamented with spinular rows on anterior surface and near outer distal margin. Basis small, with stout spinules along outer margin, and with naked outer seta. Rami three-segmented; exp-1 without inner seta, and exp-2 with one plumose inner seta. P2-P4 enp-1 with one plumose inner seta, P2 enp-2 with two inner setae.

Armature formula for swimming legs:

P5 (Fig. 2B) with separate exopod and baseoendopod. Exopod about 2.0 times as long as broad, with six setae. Baseoendopod with outer setophore carrying one seta, endopodal lobe triangular, with pore on anterior surface, with five elements.

P6 (Fig. 2A) with three setae, innermost seta longest.

Male. Total body (Fig. 7A) length 630 μm (n=2; range: 620-640 μm), measured from anterior margin of rostrum to posterior margin of caudal rami. Largest width measured at posterior margin of cephalic shield: 107 μm. Sexual dimorphism seen in A1, P1 basis, P2 endopod, P5, and P6. Urosome (Figs. 7C and 10A) six-segmented, comprising P5-bearing somite, genital somite and four free abdominal somites. Anal somite and caudal ramus as in female (Figs. 7B and 10C).

Antennule (Fig. 8) ten-segmented and haplocer. Segment 1 with one proximal and one subdistal spinular row. Segment 2 longest. Segment 5 swollen with one well-developed large aesthetasc. Segment 7 with four modified processes as figured. Segment 8 with two spiniform elements. Armature formula: 1-[1], 2-[9+1 pinnate], 3-[8], 4-[1], 5-[4+2 pinnate+(1+ae)], 6-[1], 7-[1+4 modified process], 8-[1+2 spiniform], 9-[4], 10-[5+acrothek]. Apical acrothek consisting of aesthetasc and two naked setae.

P1 (Fig. 9A). Endopod and exopod as in female. Basis with the triangular projection on the proximal inner margin, with modified inner spine (arrowed in Fig. 9A).

P2 (Fig. 9B) exopod as in female. Endopod two-segmented; enp-1 with one small inner pinnate seta; enp-2 modified, with a long sinuous apophysis distally, bearing two short inner setae, one long plumose seta, one naked long seta, and one apical geniculate seta arising from elongate cylindrical extension.

P5 (Fig. 10B). Baseoendopods of each side fused medially; endopodal lobe ornamented with spinules at outer margin, with two bipinnate spines. Exopod small, outer margin ornamented with a row of spinules, bearing five setae in total, two inner pinnate setae, a bare long distal seta and two bare outer setae.

P6 (Fig. 10A) asymmetrical, with a pinnate inner seta and two bare setae on outer distal corner.

DISCUSSION

The genus Robertgurneya was first suggested by Lang (1944), who separated the genus into two species-groups, similis-group (type: Stenhelia simulansNorman & T. Scott, 1905) and spinulosus-group (type: Amphiascus spinulosusSars, 1911), but is invalid because there is no rigid fixation for a type species. Later, R. similis A. Scott, 1896 redescribed as the type species of the genus Robertgurneya by Apostolov & Marinov (1988), so the authorship and date of this genus should be attributed as RobertgurneyaApostolov & Marinov, 1988 (Huys 2009). Robertgurneya can be identified with a specific key suggested by Lang (1965), Hamond (1973), and Gómez (2020).

The specimens from the east coast of Korea were placed in the genus Robertgurneya based on diagnostic characters defined by Lang (1944;1965) and Apostolov & Marinov (1988): forth segment of antennule with an aesthetasc, three-segmented antenna exopod, shape of mandible, and setal formula of swimming legs. The genus Robertgurneya is reported from Korean waters for the first time.

Currently, the genus Robertgurneya is divided into two groups, similis-, and rostrata-group, among which the new species belongs to the similis-group basing on the P2 enp-2 bears with two inner setae. R. donghaensis sp. nov. is closely similar to R. simulans and R. similis similis in following characters: the second segment of antenna without a seta, P1 enp-2 with inner seta, P2 enp-2 with two setae, P2 enp- 1 with inner seta, and the P5 baseoendopod with five setae in female.

However, this new species can be differentiated from the congeners by (1) rostrum not bifid at tip (usually with bifid tip in R. similis similis (Scott A. 1896;Lang 1948;Apostolov & Marinov 1988), but Apostolov (1972) gives an illustration of rostrum with a rounded apex), (2) caudal rami about as board as the length of its inner edge (caudal rami much broader than the length in R. similis similis), (3) first segment of the P1 endopod much longer than entire exopod (P1 enp-1 as long as exopod in R. simulans and R. similis similis), and (4) P5 exopod with five setae in male (P5 exopod with six setae in male R. simulans).

Including Robertgurneya donghaensis sp. nov., the number of valid species and subspecies in the genus Robertgurneya has increased to 18.