Description of two new free‐living marine nematode species of the subgenus Desmolorenzenia (Desmoscolecida, genus Desmoscolex) from Korea

Two new species of marine desmoscolecid nematodes, Desmoscolex (Desmolerenzenia) coreensis sp. nov. and D. (D.) pedunculus sp. nov., are described based on specimens obtained from the washings of shallow sublittoral invertebrates from the eastern and southern coasts of Korea. Both species possess 17 desmens and a typical setal pattern. Desmoscolex (D.) coreensis sp. nov. is most similar to D. (D.) hupferi (Steiner, 1916) in the number of desmens, setal pattern, and head shape, but differs by the structure of the cephalic setae, the cylindrically elongated end ring, and a lower “c” value. Desmoscolex (D.) pedunculus sp. nov. is closely related to D. (D.) crassicauda (Timm, 1970) in the number of desmens, setal pattern, subdorsal setae inserted on a peduncle, and a similarly shaped end ring, but is easily discernible by the globular head shape, the distinctly differentiated lip region and the position of the cephalic setae, centrally on the head capsule.


Introduction
The genus Desmolorenzenia Freudenhammer, 1975 was classified as a subgenus of the genus Desmoscolex by Decraemer (1986), which is the genus with the largest number of species in the order Desmoscolecida. Desmolorenzenia is characterized by desmens with a triangular outline and an abrupt inversion of orientation of these rings (Freudenhammer 1975;Decraemer 1985). The genus is distributed worldwide, and has been recorded from marine sediments, ranging from intertidal to deep-sea habitats, or more rarely from terrestrial environments (Steiner 1916;Lorenzen 1969;Timm 1970;Decraemer 1978Decraemer , 1986Sturhan 1982, 1997;Lal 1990).
Since Steiner (1916) first described two Desmolorenzenia species from the Atlantic Ocean (as Desmoscolex hupferi and Desmoscolex platycricus), 17 nominal species are currently recognized in this subgenus. However, the taxonomic record of Desmolorenzenia in the northwest Pacific is entirely lacking.
During a survey of the free-living marine nematofauna of Korea, two desmoscolecid species were collected from washings of sublittoral invertebrates from the eastern and southern coasts of Korea. A morphological study of several males, females, and juveniles under a differential interference microscope and a scanning electron microscope indicated that both species are new to science. They are described herein as Desmoscolex (Desmolerenzenia) coreensis sp. nov. and D. (D.) pedunculus sp. nov. and are illustrated, based on light microscopic and scanning electron microscopic (SEM) observations.

Materials and methods
The nematodes were obtained from the washings of shallow sublittoral invertebrates such as sponges (Callyspongia elegans and Cliona celata), bryozoans (Adeonella platalea and Thalamoporella lioticha), and polychaetes (Pomatoleios krausii and Serpula vermicularis). All material was collected from depths between 3 and 25 m by scuba diving on the eastern and southern coasts of Korea ( Figure 1). In the field, samples were soaked in freshwater for less than a minute for osmotic shock (Kristensen 1989). Nematodes were decanted and sieved through a fine-mesh net with a mesh size of 67 mm. The filtered specimens were fixed in 4% buffered formalin in sea water.
Specimens were mounted in anhydrous glycerin between two coverslips on H-S slides (Shirayama et al. 1993), a recently developed type of the Cobb slide, observed, measured, and photographed using a differential interference contrast microscope (Olympus BX-60) equipped with Nomarski optics. All drawings were made with the aid of a camera lucida. Specimens for SEM study were prefixed for 4-6 h at 4uC in 2.5% glutaraldehyde in 0.1 M phosphate buffer (pH 7.4), followed by post-fixation with 2% cold osmium tetroxide in the same buffer for 1.5-2 h. After dehydration through a graded series of ethanol (50-100% at 10% intervals of 30 min each), the specimens were critical-point dried, coated with goldpalladium, and electron-micrographed using a Hitachi S-520 scanning electron microscope, at 15 kV voltage acceleration. Terminology mostly follows Decraemer (1986).
Abbreviations used in the text are as follows: L, body length; hd, maximum head diameter; cs, length of cephalic setae; sd n , length of subdorsal somatic seta on desmen n; sv n , length of subventral somatic seta on desmen n; ph, length of pharynx; t, tail length; tmr, length of terminal ring; tmrw, maximum width of terminal ring; mbd, maximum body diameter; mbde, maximum body diameter, external material not included; spic, length of spicules measured along the median line; gub, length of gubernaculum; V%, distance of vulva from anterior body end as percentage of total body length; a, b, c, proportions of de Man: a, body length divided by body maximum width; b, body length divided by the pharynx length; c, body length divided by the tail length. All measurements are in micrometres (mm); mean values are provided between parentheses.

Species descriptions
Order DESMOSCOLECIDA Family

Type habitats
The nematodes were obtained from sponges and bryozoans on subtidal rocks (25 m deep), collected by scuba diving.

Etymology
The specific name, coreensis, alludes to the type locality of the new species.
Head wider than long, rounded (Figures 2A, 3A, B), anteriorly tapered and truncated, and posteriorly with more or less cylindrical neck-region. Head cuticle completely covered with thin layer of fine granular desmos, except in amphideal zone. Labial region not distinct, apparently without separate lips. Labial sensilla not observed. Cephalic setae, 22 mm long, shorter than head width; jointed distally, i.e. finer distal part socketed into broad, cylindrical basal part near the tip of setae (Figure 2A, C, E); setae inserted directly on head cuticle just anterior to mid-head. Amphideal fovea (Figures 2A, 3B, C) rounded, largely covering head laterally; extending anteriorly to truncated end and posteriorly beyond level of insertion of cephalic setae. Small buccal opening leading to thin-walled stoma, 7 mm in length. Oesophagus not observed in holotype, but extending to end of desmen 3 in paratypes ( Figure 2C).
Tail consisting of two desmens (Figures 2A, 3D). End ring, 49 mm long, about 2.3 times longer than wide, consisting of broad cylindrical anterior part, extending up to insertion of terminal subdorsal somatic setae, and ventrally bent posterior part, tapering towards short, uncovered spinneret. End ring, with exception of terminal spinneret, totally covered with layer of secretion and foreign material. Caudal glands not observed.

Diagnosis
Desmoscolex (Desmolorenzenia) coreensis sp. nov. is characterized by the following combination of characters: (1) presence of 17 desmens and typical desmoscolecid setal pattern (nine pairs of subdorsal somatic setae and eight pairs of subventral somatic setae); (2) globular head with truncated anterior end; (3) cephalic setae jointed distally, i.e. a finer tip socketed into broad, cylindrical basal part; (4) presence of a pair of ocelli situated between desmens 3 and 4; (5) somatic setae directly inserted on to cuticle; and (6) shape of end ring with a broad, cylindrical anterior part ranging up to insertion of posteriormost subdorsal somatic setae, and a ventrally bent terminal part tapering towards short naked spinneret.
For differential diagnosis, see Discussion.
Order DESMOSCOLECIDA Family

Type habitats
The nematodes were obtained from shallow subtidal invertebrates (sponges, bryozoans, and polychaetes), which were collected from depths of 3 to 5 m by scuba diving.

Etymology
The specific name, pedunculus, refers to the well-developed peduncles of insertion of both subdorsal and subventral somatic setae.
Head globular, wider than long, anteriorly tapered and truncated, and posteriorly with more or less cylindrical neck-region ( Figures 4A, B, 5A, 6A). Cephalic cuticle completely covered with thin layer of fine granular desmos, except in amphideal zone. Labial region ( Figures 4B, 5C, D) hexagonal, offset with separate lips. Circle of six minute, papilliform labial sensilla situated near edge of oral aperture ( Figure 5C). Specialized cephalic tubercles situated between cephalic tubercles and labial sensilla. Elliptical cephalic tubercles arranged in single crown near labial sensilla. Outer margin of lip region surrounded by well-developed cephalic ridge. Cephalic setae ( Figure 4A, B) tapering distally, 19 mm in length, shorter than head width. Cephalic setae jointed distally, i.e. finer distal part socketed into broad, cylindrical basal part near the tip of setae ( Figures 4B, E, 5C, D), inserted on peduncles just anterior to mid-head. Amphideal fovea ( Figure 4B) rounded, largely covering head laterally, situated at level of mid-head.
Digestive system typical of Desmolorenzenia. Buccal opening with minute buccal cavity. Oesophagus 59 mm long, posteriorly extending to level of posterior margin of desmen 3 ( Figure 4A); intestine dorsal to reproductive system. Ocelli not observed. Reproductive system typical of Desmoscolecidae: single outstretched testis, extending up to level between desmens 6 and 7 ( Figure 4A). Ejaculatory glands not observed. Spicules relatively short (26 mm long) ( Figure 4A, C), nearly straight; blade tapering caudally to pointed tip, proximally provided with well-developed offset capitulum. Gubernaculum thin, troughshaped, 6 mm long, adjacent to tip of spicules. Cloacal tube broad, clearly protruding from medioventral body wall in desmen 15 ( Figure 4A, C).
Tail with two desmens ( Figure 4A). End ring 39 mm long, about 2.4 times longer than wide, consisting of broad cylindrical anterior part extending up to insertion of terminal subdorsal somatic setae, and ventrally bent terminal part, tapering towards well-developed naked spinneret. End ring, with exception of terminal spinneret, totally covered with desmos. Caudal glands not observed.

Diagnosis
Desmoscolex (Desmolorenzenia) pedunculus sp. nov. is mainly characterized by the following combination of characters: (1) presence of 17 desmens with inversing desmen 14 and typical desmoscolecid setal pattern (nine pairs of subdorsal somatic setae and eight pairs of subventral somatic setae); (2) globular head with well-developed lip region, provided with six minute labial sensilla; (3) hexagonal cephalic ridge and numerous cephalic tubercles surrounding lip region; (4) cephalic setae jointed at their distal part; (5) presence of peduncle for both subdorsal and subventral somatic setae; and (6) end ring with broad, cylindrical anterior part, extending up to insertion of posteriormost subdorsal somatic setae, and ventrally bent terminal part tapering towards a well-developed naked spinneret.
For differential diagnosis, see Discussion.
Desmoscolex ( During a SEM observation of Desmoscolex (D.) pedunculus sp. nov., we observed the ultrastructure in the labial region which was previously unknown (Shirayama and Hope 1992;Decraemer and Sturhan 1997). Hitherto, the ultrastructure of the lip region in the subgenus Desmolorenzenia was known from only two species: D. (Desmolorenzenia) sp. 1 from a marine habitat (Shirayama and Hope 1992)  (2) presence of six well-developed labial sensilla (versus not welldeveloped); and (3) the shape of cephalic tubercles (relatively thick and short versus thin and long).