INTRODUCTION

The family Phanodermatidae Filipjev, 1927 consists of two subfamilies and nine genera, as the apparent cosmopolitan distribution of free-living marine nematodes (Smol et al. 2013). The family Phanodermatidae is characterized by the presence of a head capsule, small buccal cavity, and cellular structure in the pharyngeal region (Inglis 1964;Lorenzen 1981;Platonova 1984;Smol et al. 2013). The family Phanodermatidae is classified into two subfamilies according to the structure of the complex pharyngeal-cephalic capsule (Platonova 1984). The subfamily Phanodermatinae Filipjev, 1927 is characterized by having a well-developed cephalic capsule and pharyngeal capsule with one small dorsal and two large subventral outgrowths that point forward, and is composed of two genera, PhanodermaBastian, 1865 and MetaphanodermaPlatonova, 1984.

The genus Phanoderma was first erected by Bastian (1865), most of which discovered in various marine habitats (Gerlach and Riemann 1974). After that, 11 species of the genus Phanoderma were transferred to the genus Metaphanoderma by Platonova (1984). Consequently, 22 valid species are currently recognized in the genus Phanoderma (Wieser 1953;Gerlach and Riemann 1974;Lorenzen 1981;Platonova 1984;Zograf et al. 2015). It can be distinguished from other genera of this family in having the attenuated head, well-developed cephalic capsule and pharyngeal capsule, and a tubular precloacal supplement (Smol et al. 2013;Zograf et al. 2015).

During a survey of the free-living marine nematodes of Korea, a new species of the genus Phanoderma was obtained from washings of sediments from rocky intertidal seagrass bed of the East Sea, Korea. In the present study, we provide taxonomic descriptions and illustrations of the new marine nematode using differential interference contrast (DIC) microscope. This is the first taxonomic report on the genus Phanoderma in the East Sea, Korea.

MATERIALS AND METHODS

Sampling of taxa. The marine nematodes were obtained from washings of intertidal sediments, which were collected from rocky intertidal seagrass bed on the eastern coast of Korea. Samples were filtered through a sieve with 67 μm mesh in the field after freshwater rinsing for less than a minute for osmotic shock, and then fixed in 5% formalin (Kristensen 1989).

Sample processing and preparation of specimens. The nematodes were sorted from the mixed meiobenthos under LEICA 205 C stereomicroscope. The nematodes were transferred to glycerol and mounted between two cover slips on a double sided slide for morphological observations (Shirayama et al. 1993).

Light microscopy. Specimens were measured, examined and drawn using Nomarski differential interference contrast (DIC) with an Olympus BX53 microscope equipped with a drawing tube and a Olympus DP26 digital camera with Olympus CellSens corresponding imaging software.

Terminology and abbreviations. Measurements are in μm. Abbreviations used in the text are as follows: a, body length divided by maximum body diameter; abd, anal body diameter; b, body length divided by pharynx length; bcl, length of buccal cavity; bcw, width of buccal cavity; bd, body diameter at the base of pharynx; c, body length divided by tail length; cs, cephalic setae length; dps, distance of the precloacal supplement from cloacal opening; ep, distance from anterior to anterior edge of excretory pore; gub, gubernaculum length; hd, diameter at the level of cephalic setae; L, total body length; M, maximum body diameter; N (%), nerve ring distance from the anterior end as percentage of pharynx length; nr, distance from anterior end to nerve ring; ol, distance from anterior end to anterior edge of ocelli; ph, pharynx length; spic, spicules length; sup, precloacal supplement length; t, tail length; v, distance from anterior end to vulva; V (%), vulva distance from anterior end as percentage of total body length.

SYSTEMATIC ACCOUNTS

Class Enoplea Inglis, 1983

Order Enoplida Filipjev, 1929

Family Phanodermatidae Filipjev, 1927

Genus PhanodermaBastian, 1865

Type species

Phanoderma cocksi Bastian, 1865

Other valid species

Phanoderma albidumBastian, 1865

Phanoderma annulocaudatumAllgén, 1939

Phanoderma brachyductumWieser, 1953

Phanoderma coecumAllgén, 1947

Phanoderma hawaiienseAllgén, 1951

Phanoderma islandicumDitlevsen, 1926

Phanoderma laticolle (Marion, 1870)

Phanoderma longisetumAllgén, 1939

Phanoderma macrolaimum (Linstow, 1908)

Phanoderma nasutumSchuurmans Stekhoven, 1950

Phanoderma nectaGerlach, 1957

Phanoderma ocellatum (Cobb, 1920)

Phanoderma paracampbelliAllgén, 1958

Phanoderma rigidumSchuurmans Stekhoven, 1946

Phanoderma robustumAllgén, 1957

Phanoderma segmentumMurphy, 1963

Phanoderma serratumDitlevsen, 1930

Phanoderma setigerum (Marion, 1870)

Phanoderma steineriDitlevsen, 1918

Phanoderma tenuicaudatumAllgén, 1951

Phanoderma unicumInglis, 1964

Phanoderma koreense sp. nov. (Figs. 1-3; Table 1)

Type material. Holotype. Male, slide (KIOST NEM-1- 2486) deposited in the nematode collection at the specimen conservation room of the Bio-Resources Bank of Marine Nematodes (BRBMN), Korea Institute of Ocean Science & Technology.

Paratypes. Seven paratypes, four males (KIOST NEM-1- 2487-KIOST NEM-1-2490) and three females (KIOST NEM-1-2491-KIOST NEM-1-2493) deposited in the nematode collection at the specimen conservation room of the Bio-Resources Bank of Marine Nematodes, Korea Institute of Ocean Science & Technology. All the specimens collected on 29 June 2017 from the type locality by HJ Lee. All are mounted in anhydrous glycerin between two coverslips on double sided slide, sealed with nail polish.

Etymology. The specific name is taken from the Korea, the type locality.

Type locality and habitat. Jumun-ri, Jumunjin-eup, Gangwon- do, Korea (37°54ʹ23.76″N, 128°49ʹ39.40″E). 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 sampler. Sediments were composed of tiny shell gravels and coarse detritus.

Diagnosis. Head attenuated. Six inner labial sensilla present as minute papillae around with circular groove. Well-developed trifurcate pharyngeal capsule, and cephalic capsule with posteriorly bearing longitudinal striations. Two very small tooth-like subventral projection part present. Long and slender spicules with 4-5 serrated distal end, beyond precloacal supplement. Gubernaculum short and thick. A series of eight to nine stout and short setae present on ventral cloacal region. Conico-cylindrical tail with two pairs of blunt setae in both sexes.

Measurements. See Table 1 for detailed measurements and morphometric ratios.

Description. Males: Body long (3,746-4,233 μm), typically cylindrical appearance (Fig. 1A). Anterior end gradually narrow just in front of nerve ring, cervical region 4-5 times thinner than rest of body region. Maximum body diameter at mid body level 104-122 μm. Cuticle smooth and thick with a few scattered short somatic setae throughout body. Head diameter 21-27 μm, distinctly narrowed. Six inner labial sensilla present as minute papillae around with circular groove (Figs. 1C, 3B). Six outer labial sensilla and four cephalic setae in one circle; cephalic setae 11-12 μm long, 45-52% of head diameter. Buccal cavity small but surrounded by cuticular capsules without teeth. Well-developed trifurcate pharyngeal capsule with big and wide extremely sclerotized outgrowths (Figs. 1C, 3A). Two tooth-like subventral projection part present, very small and cuticularized. Cephalic capsule with solid structure divided into two parts: anterior section with thick walls and without grooves, and posterior section with relatively thin walls and longitudinal striations (Figs. 1C, 3B). Amphids inconspicuous, ocelli 7 μm wide, located at 38-45 μm from anterior end (Fig. 1C). Pharynx muscular, 831-915 μm long, cylindrical anteriorly and enlarged at posterior end with characteristic crenelated outline. Excretory pore conspicuous, situated at 86-95 μm from anterior end. Nerve ring encircling pharynx, situated at 36-40% of pharynx length from anterior end (Fig. 1B). Tail 135-142 μm long, consists of proximal conical and distal cylindrical parts with two pairs of blunt setae (Figs. 1D, 3D). Spicules elongated, strongly curved, 191-219 μm long, extend beyond precloacal supplement, distally sharpened with 4-5 serrated distal end (Fig. 1E). Gubernaculum 38-42 μm, relatively short and thick. Precloacal supplement tubular shaped, 39-43 μm long, situated at 114-137 μm in front of cloacal opening, about 53-65% of spicules length. Conspicuous 8-9 stout, short setae located on ventral cloacal region in a row (Figs. 1D, 3C).

Females: Similar to male in general appearance (Fig. 2B, D). Body length 4,263-4,367 μm with cylindrical body, distinctly tapering anterior end. Maximum body diameter at mid body level 120-130 μm (Fig. 2A). Reproductive system didelphic, ovary symmetrical, reflexed. Vulva 2,396- 2,484 μm from anterior end, situated at 55-58% of total body length (Fig. 2C). Tail length 177-188 μm long, about 2.6-2.7 times of anal body diameter. Conico-cylindrical tail with two pairs of blunt setae (Fig. 2E).

Differential diagnosis and relationships.Phanoderma koreense sp. nov. is characterized by the combination of the following features: (1) the presence of well-developed trifurcate pharyngeal capsule and cephalic capsule with posteriorly bearing longitudinal striations; (2) six inner labial sensilla present as minute papillae around with circular groove (3) long and slender spicules with 4-5 serrated distal end, beyond the precloacal supplement; (4) the presence of relatively short, thick gubernaculum; (5) a series of eight to nine stout and short setae located on the ventral cloacal region; and (6) conico-cylindrical tail with two pairs of blunt setae in both sexes. Phanoderma koreense sp. nov. is closely related P. cocksiBastian, 1865 and P. serratumDitlevsen, 1930 based on very long and slender spicules with serrated distal end and cephalic capsule with posteriorly longitudinal striations. However, Phanoderma koreense sp. nov. differs from P. cocksi by the length (c=27-31 vs. c=35 in Gerlach 1962) and shape (conico-cylindrical vs. conical) of tail in males, and present of eight to nine stout and short setae located on the ventral cloacal region (absent in P. cocksi). Phanoderma koreense sp. nov. is distinguished from P. serratum by the relatively longer spicules (191- 219 μm vs. 154 μm), shorter tail in males (c=27-31 vs. c=35.7), and the presence of conspicuous gubernaculum.

Phanoderma koreense sp. nov. also resembles P. ocellatum (Cobb, 1920) and P. segmentumMurphy, 1963, mainly by possessing the conico-cylindrical tail and long spicules stretched over the precloacal supplement. However, Phanoderma koreense sp. nov. is distinguished from P. ocellatum by having the longer body size (3,746-4,233 μm vs. 2,600 μm in male), spicules with serrated distal end, and a series of eight to nine stout and short setae on the ventral cloacal region. Phanoderma koreense sp. nov. differs from P. segmentum by relatively shorter body length in males (3,746-4,233 μm vs. 4,750 μm in Murphy 1963), more slender body shape in males (a=34-38 vs. a=44 in Murphy 1963), and the presence of spicules with serrated distal end (absent in the original description of P. segmentum). Also, Phanoderma segmentum have five distinct segments of the spicules, a feature not shared by Phanoderma koreense sp. nov.

Taxonomic remarks. The genus PhanodermaBastian, 1865 differs from the other genera of this family in having the attenuated head, well-developed pharyngeal capsule and cephalic capsule, and a tubular precloacal supplement (Smol et al. 2013;Zograf et al. 2015). The checklist of the genus Phanoderma has been recorrected in detail by Gerlach and Riemann (1974) including their synonymy and repeated findings. Phanodermopsis nectaGerlach, 1957 was relocated to Phanoderma on the basis of the presence of a precloacal supplement (Lorenzen 1981;Zograf et al. 2015). Platonova (1984) rearranged 11 species of the genus Phanoderma into the genus Metaphanoderma on the basis of the morphological differences, such as the shape of pharyngeal and cephalic capsule. However, the descriptions of several species are insufficient, depicting very few characteristics and providing poor illustrations of the important characteristics of cephalic and spicule structures, and many species descriptions were based on only females or juveniles (Platonova 1984;Zograf et al. 2015). Consequently, 22 valid species are recorded in the genus Phanoderma (Wieser 1953;Gerlach and Riemann 1974;Lorenzen 1981;Zograf et al. 2015). We herein provide a pictorial identification key to species of the genus Phanoderma (Fig. 4). The illustration of Phanoderma macrolaimum (Linstow, 1908) could not be found in the original description, however, we analyzed and differentiated the taxonomic key characters based on the original description of the species.