INTRODUCTION

The genus Enoplus Dujardin, 1845 is currently composed of 36 valid species, one of the largest dominant species in the intertidal zone, and having a cosmopolitan distribution. The genus Enoplus Dujardin, 1845 is easily distinguished by its three solid mandibles without teeth, low lips with inner labial papilliform, and the presence of specific precloacal supplement (Platt and Warwick 1983). In this genus, most species known can be separated among species according to the shape of the male genital armature, spicules and gubernaculum (Wieser 1953).

Most taxonomic studies of free-living marine nematodes have been conducted in Europe. Recently several papers of free-living marine nematodes have been published on China and Japan (Shimada and Kajihara 2014; Chunming et al. 2015). Until now, only seven Enoplus species, E. anisospiculus Hopper, 1968, E. kurilensisFadeeva and Yushin, 1998, E. michaelseni Linstow, 1896, E. paralittoralisWieser, 1953, E. paralphaFadeeva and Yushin, 1998, E. taipingensisZhang and Zhou, 2012, and E. velatus Wieser, 1959, have been recorded in the Northwest Pacific Ocean (Kito 1976; Yoshimura 1980; Fadeeva and Yushin 1998; Zhang and Zhou 2012). Up to now, 40 free-living marine nematodes of the family Draconematidae, Comesomatidae, and Enchelidiidae have been recorded from Korea (Rho and Min 2011; Barnes et al. 2012; Hong and Lee 2014). However, the taxonomic report on the genus Enoplus of Korea in the intertidal algae is entirely unknown. The purpose of this study is to report taxonomic description of three unrecorded species belonging to genus Enoplus collected from rocky intertidal seagrass on the eastern coast of Korea.

MATERIALS AND METHODS

1.Sampling

Marine nematodes were obtained from washing of intertidal sediment. Samples were collected from rocky intertidal seagrass on the eastern coast of Korea. Samples were filtered through a 67 μm mesh sieve in the field after freshwater rinsing for less than a minute for osmotic shock (Kristensen and Higgins 1989), and then fixed in 5% formalin in sea water. Coarse detritus and tiny shell gravels were removed from the sample by decantation and the meiobenthos was roughly extracted by flotation in Ludox (Dupont) HS 40 (Burgess 2001).

2.Observation and drawing

The specimens were sorted from the mixed meiobenthos under LEICA 205C stereomicroscope. The specimens for morphological observation were transferred to anhydrous glycerin between two cover slips on a H-S slide (Shirayama et al. 1993). Specimens were examined, photographed and drawn using Nomarski differential interference contrast (DIC) with an Olympus BX53 microscope equipped with a drawing tube and a DIXI 3000 camera, and quality enhanced portable photoshop software. Specimens selected for scanning electron microscopy (SEM) were fixed in 5% formalin, washed in distilled water, and critical point dried. Specimens were coated with gold/palladium, and examined with mini 4500 SEM.

3.Terminology and abbreviations

Abbreviations are as follows: L, total body length; esol, esophagus length; a, body length/max. body diameter; hd, head diameter on cephalic setae; b, total body length/esophagus length; c, total body length/tail length; bd, body diameter at the base of esophagus; M, maximum body diameter; cs, cephalic setae; mandl, mandibles length; nr, anterior end to nerve ring; nr (%), nr/esol; supl, supplement; spil, spicules length; abd, anal body diameter; s′, spi/abd; gubL, gubernaculum length; t, tail length; t/abd, tail length/abd; V, anterior end to vulva; V (%), V/L.

SYSTEMATIC ACCOUNTS

Class Enoplea Inglis, 1983

Order Enoplida Filipjev, 1929

Family Enoplidae Dujardin, 1845

Genus Enoplus Dujardin, 1845 갑옷선충속 (신칭)

1.E noplus taipingensis Zhang and Zhou, 2012 타이핑갑옷선충 (신칭)

Synonym: Enoplus taipingensisZhang and Zhou, 2012, p. 102, Figs. 2-4.

Material examined: 5♂♂ and 3♀♀, Bugu-ri, Uljin-gun, Gyeongsangbuk-do, Korea (37°06′21.39″N, 129°22′37.42″ E), collected on 14 July 2014. The specimens are deposited in the nematode collection of the Korea Institute of Ocean Science and Technology, Uljin, Korea. All are mounted in anhydrous glycerin between two coverslips on H-S slides, sealed with nail polish.

Diagnosis: Cuticle smooth; trumpet-shaped precloacal supplement present; spicules with five to eight semi-circular plates; tail with a series of lateral setae.

Measurements: See Table 1.

Description: Male: Body length 5,987~7,059 μm long, large, rather stout, slightly tapers to anterior region (Fig. 2A). Maximum body diameter 177~218 μm. Cuticle smooth and thick. Head bluntly rounded, typically with three low lips. Head with inner circle of six prominent labial papillae and outer circle of 10 (6+4) cephalic setae, six longer setae 26 ~33 μm, 32~48% of the head diameter. Mandibles solid, 26~33 μm wide, measured across anterior extremity, about 34~43% of the head diameter on cephalic setae (Figs. 1A, 2B, 3A). Amphids openings small rounded pocket-like, situated at between anterior to posterior edge of cephalic capsule (Fig. 3B). Three short lateral cervical setae situated at posterior to cephalic capsule, arranged in triangle. Esophagus cylindrical, 846~1,095 μm. Nerve ring encircling esophagus, 388~440 μm from anterior end, situated at 35~45 % of esophagus length from anterior end. No definite eyespots. Dark brown pigment diffuse present anteriorly and variable in form (Fig. 2B). Cervical and somatic setae stout, sparsely distributed throughout body along dorsal and ventral margins of lateral hypodermal chords. Spicules symmetrical, curved, 272~311 μm long, inflated proximally and pointed distally, and provided with hook shaped 5~8 semicircular plates (Figs. 1B, 2E, 3D-G). Two pairs of stout setae situated at posterior lip of cloacal opening. Long stout setae present on subventral sides between openings of supplement and of precloacal region (Figs. 1B, 2C). A series of lateral setae situated throughout tail (Fig. 3I). A piece of gubernaculum 97~103 μm long, with lateral projections. Pre-cloacal supplement trumpet-shaped with well-dilated proximal end, 113~127 μm long (Figs. 1B, 2D, 3H). Tail conico-cylindrical, 320~366 μm long, about 2.4~2.6 times of anal body diameter (Figs. 1C, 2F, 3C).

Female: Similar to male in general appearance. Body length 5,448~7,273 μm long; maximum body diameter 189~229 μm. Reproductive system monodelphic, with two opposed, reflexed ovaries. Vulva 3,890~4,110 μm from anterior end, situated at 57~ 60% of total body length (Fig. 2G). Tail length 328~374 μm long, about 2.6~2.9 times of anal body diameter (Fig. 2H.

Remarks: Enoplus tapingensis Zhang and Zhou, 2012 was firstly described in the Taiping Bay, Chingdao, China. Enoplus tapingensis has been previously reported from only type locality. The Korean specimens were discovered from the seagrass bed of intertidal rocky shore of the East Sea, Korea. Enoplus tapingensis is characterized by longer body size, a series of lateral setae throughout the tail in male, and the presence of spicules with five to eight semi-circular plates and precloacal supplement with three projections in distal end. Enoplus taipingensis is most like E. michaelseni Linstow, 1896 by possessing trumpet-shaped precloacal supplement and similar spicules structure with semi-circular plates. However, E. taipingensis can be significantly different from E. michaelseni by longer body length (5,987~7,060 μm vs. 3,360~4,800 μm), slightly larger spicules length (206~232 μm vs. 174~192 μm in Yoshimura 1980), and the presence of special series of lateral setae throughout the tail in male. The present Korean specimens agree well with Zhang and Zhou’s (2012) original description, especially in the number of three lateral cervical setae arranged in triangle and the presence of characteristic lateral setae of throughout the tail in male. However, the Korean specimens of E. taipingensis are not well accorded with the original description by having a longer precloacal supplement length (115~ 127 μm vs. 62~83 μm).

Habitat: The nematodes were obtained from the sediments of rocky intertidal seagrass bed on the eastern coast of Korea collected at a depth of 1 m by hands with scoop. Sediments include tiny shell gravels and coarse detritus.

Distribution: China, Korea.

Deposition: KIOST NEM-1-43, KIOST NEM-1-44, KIOST NEM-1-45, KIOST NEM-1-46, KIOST NEM-1-47, KIOST NEM-1-50, KIOST NEM-1-51, KIOST NEM-1-52.

Identifiers: Hyo Jin Lee.

2.E noplus meridionalis Steiner, 1921 남방갑옷선충 (신칭)

Synonyms: Enoplus communis var. meridionalis Steiner, 1921, p. 30.

Enoplus meridionalis: Inglis, 1971, p. 71, Figs. 20-26.

Material examined: 3♂♂, Bugu-ri, Uljin-gun, Gyeongsangbuk- do, Korea (37°06′21.39″N, 129°22′37.42″E), collected on 9 July 2014 by Hyo Jin Lee; Jangsa-dong, Sokchosi, Gangwon-do, Korea (38°13′37.77″N, 128°35′16.92″E), collected on 2 Oct 2014. Two specimens are deposited in the nematode collection of the Korea Institute of Ocean Science and Technology, Uljin, Korea. One specimen is kept in the collection of the authors. All are mounted in anhydrous glycerin between two coverslips on H-S slides, sealed with nail polish.

Diagnosis: Cuticle smooth; trumpet-shaped precloacal supplement with slightly dilated proximal end; massive spicules present; tail with two pairs of stout terminal setae. Measurements: See Table 2.

Description: Male: Body length 3,339~4,194 μm long, slender and cylindrical, slightly tapers to anterior region (Fig. 5A). Maximum body diameter 95~119 μm. Cuticle smooth and thick. Head extended, typical with three low lips and inner circle of six prominent labial papillae. Head with outer circle of 10 (6+4) cephalic setae, six longer setae 15.3~16.6 μm long, about 0.3~0.4 of head diameter. Mandibles solid, 12~13 μm wide, measured across anterior extremity, about 27~32% of head diameter on cephalic setae (Figs. 4A, 5B). Amphids openings small rounded pocket- shaped; situated at between anterior to the posterior edge of the cephalic capsule. Esophagus cylindrical, 470~578 μm. Eyespot present (Fig. 4A). Few setae 3~4 μm long, scattered throughout anterior esophageal region, and three stout setae on each side in behind eyespot. Tail cylindrical; ends in slight swelling with four subterminal setae, 219~ 233 μm long, about 2.6~2.9 times of anal body diameter (Figs. 4B, 5E). Spicules symmetrical, curved, 106~131 μm long; gubernaculum, 34~40 μm long, with lateral projections (Figs. 4B, 5D). Two pairs of stout setae situated on posterior lip of cloacal opening. Precloacal region with long and stout subventral setae; longest setae 18~20 μm long (Fig. 5C). Precloacal supplement, 55~73 μm long, trumpetshaped with slightly dilated proximal end (Figs. 4E, 5D).

Remarks: Enoplus meridionalis Steiner, 1921 is mainly characterized by the following combination of characters: the presence of trumpet-shaped precloacal supplement with slightly dilated proximal end, different shaped massive paired spicules and tail with two pairs of stout terminal setae. Enoplus meridionalis is most related to E. heardensis Mawson, 1958 and E. harlockaeInglis, 1964 by having a trumpet- shaped precloacal supplement. However, E. meridionalis is easily discernible from the two morphologically related species by the shape of gubernaculum (the median and the lateral pieces of gubernaculum slightly curve posterior to the spicules in E. meridionalis vs. the median and the lateral pieces curve upwards to enfold the spicules in E. harlockae) and having a shorter gubernaculum length (34~40 μm in E. meridionalis vs. 70~80 μm in E. heardensis). The present Korean specimens agree well with Steiner’s (1921) original description, especially in the shape of pre-cloacal supplement, spicules and gubernaculum. However, the Korean specimens of E. meridionalis are not well accorded with the original description by having a slightly longer body length (3,339~4,194 μm vs. 2,531~2,545 μm).

Habitat: The nematodes were obtained from the sediments of rocky intertidal seagrass bed on the eastern coast of Korea collected at a depth of 1 m by hands with scoop. Sediments include tiny shell gravels and coarse detritus.

Distribution: America, Australia, North Atlantic, Korea.

Deposition: KIOST NEM-1-369, KIOST NEM-1-372, NEEN- 11.

Identifiers: Hyo Jin Lee.

3.E noplus mammillatusTimm, 1959 유두돌기갑옷선충 (신칭)

Synonym: Enoplus mammillatusTimm, 1959, p. 205, Pl. 1.

Material examined: 1♂, Namae-ri, Yangyang-gun, Gangwon- do, Korea (37°06′21.39″N, 129°22′37.42″E), collected on 15 July 2014. The specimen is deposited in the nematode collection of the Korea Institute of Ocean Science and Technology, Uljin, Korea. All are mounted in anhydrous glycerin between two coverslips on H-S slides, sealed with nail polish.

Diagnosis: Cuticle smooth; narrow tubular-shaped precloacal supplement present; spicules with cephalated posterior end.

Measurements: See Table 2.

Description: Male: Body length 3,238 μm long, elongated cylindrical, tapered slightly to the anterior end (Fig. 6A). Maximum body diameter 90.6 μm. Cuticle smooth. Head rounded, 39.5 μm wide, typically with three low lips; each lips surrounded by inner circle of six small labial papillae. Head with 10 cephalic setae, six longer setae 13.8 μm, about 0.3 times of head diameter and four shorter setae 10.7 μm. Mandible well-developed, 11.7 μm wide, 16 μm long, about 30% of the head diameter at cephalic setae (Figs. 4C, 6B). Amphids opening small rounded pockets, 5 μm wide, 7 μm long, located anterior to base of cephalic capsule (Fig. 6C). Esophagus cylindrical, 486 μm long. Broadly spreading eye pigment located in anterior end of esophagus (Fig. 4C). Cervical-somatic setae about 4 μm long, scattered throughout body along subdorsally and subventrally. Tail cylindrical, with a pair of terminal setae posterially. Tail length 218 μm long, about 2.5 times of anal body diameter (Figs. 4D, 6E). Spicules, 103 μm long, massive, symmetrical, slightly curved toward cephalated posterior end. Gubernaculum 35.7 μm long, slightly triangular shaped with lateral projections. Precloacal supplement narrow strait-shaped, 53.6 μm long (Figs. 4D, 6D). Precloacal lip opening with a pair of stout cloacal setae. Long stout setae located on between openings of supplement and precloacal region, the longest setae 23.5 μm (Fig. 4D).

Remarks: Enoplus mammillatusTimm, 1959 was firstly described from the Arabian Sea. Enoplus mammillatus is easily distinguished from the other species of the genus by narrow tubular-shaped precloacal supplement. This species is morphologically similar to E. benhami Ditlevsen 1930, E. micrognathus Allgen 1947, and E. paralphaFadeeva and Yushin, 1998 by narrow tubular-shaped precloacal supplement. However, E. mammillatus can be significantly different from E. benhami by longer precloacal supplement length (54 μm vs. 33 μm). Enoplus micrognathus differs from E. mammillatus by the position of precloacal supplement, which is very closely located in front of the anus. Also, E. mammillatus has spicules of posterior end with hooks, but E. paralpha has only smooth spicules. The present Korean specimen collected from rocky intertidal seagrass on the eastern coast of Korea is also very similar with E. mammillatus. Most taxonomic characters of the present specimen are very similar with the original description of E. mamillatus, but the Korean specimen has no semicircular plate in spicules.

Habitat: The nematodes were obtained from the sediments of rocky intertidal seagrass bed on the eastern coast of Korea collected at a depth of 1 m by hands with scoop. Sediments include tiny shell gravels and coarse detritus.

Distribution: Arabian Sea, Korea.

Deposition: KIOST NEM-1-398.

Identifiers: Hyo Jin Lee.