Three new species of free‐living marine nematodes from the Bohai Sea and Yellow Sea, China

Three new species of marine nematodes belonging to the genera Paranticoma (family Anticomidae) and Parodontophora (family Axonolaimidae) are described from the Bohai Sea and Yellow Sea. Paranticoma tricerviseta sp. nov. is similar to P. bandaenseMicoletzky and Kreis, 1930 in the spicules, but can be distinguished by the presence of a ventral projection on the spicules, three regularly arranged cervical setae in both the male and female, and two distinct ventral setae behind the anus. Parodontophora deltensis sp. nov. is close to P. paragranulifera (Timm, 1952) in the length of the amphids, with the ventral arm of the amphid extending past the base of the stoma, but can be separated by the ratio of dorsal arm length to ventral arm (0.36–0.55 versus 0.20–0.25) and the position of the excretory pore (at the middle level versus top level of the stoma), distinctive cervical setae arrangement and a longer renette cell. Parodontophora wuleidaowanensis sp. nov. is close to P. danker Belogurov and Kartavtseva, 1975 in the form of the amphids, but can be distinguished by the longer length of the ventral arm of the amphids and the distinctive arrangement of cervical setae.


Introduction
During a Sino-UK Joint ''Darwin Initiative'' survey in the Bohai Sea from 1997 to 1999, and also a Sino-US Joint Investigation on Sedimentary Dynamics of the Submarine Delta in the Huanghe River Estuary and its adjacent waters from 1985 to 1987, many previously undescrihed species were encountered. These were studied both at the Ocean University of China, Qingdao and at the Plymouth Marine Laboratory, UK. A series of papers on the environmental features, macrobenthos and meiobenthos (marine nematodes in particular) of the Bohai Sea have been published (Zhang et al. , 1993(Zhang et al. , 1994. Systematic papers on marine nematodes have been published by Zhang (1990Zhang ( , 1991Zhang ( , 1992, Zhang and Platt (1983), Hope and Zhang (1995), Guo and Zhang (2000), and . In this paper we describe three new species, Paranticoma tricerviseta sp. nov., Parodontophora deltensis sp. nov., and P. wuleidaowanensis sp. nov., with a key to the species of Paranticoma and a tabular key to the species of Parodontophora with longer amphids.

Methods
Specimens of Paranticoma tricerviseta sp. nov. were collected from station B9761, the central part of the Bohai Sea during the June/July cruise of the R/V No.1 Science in 1997 at a depth of 26 m from a sediment of fine sand-clay, and also from station D5 with R/V No.2 Dong Fang Hong during the October/November cruise in 1998. Specimens of Parodontophora deltensis sp. nov. were collected from submarine delta stations E2, E10 and T7, and Lai Zhou Bay stations DA2 and DA4 during the July/August cruise of R/V No.1 Dong Fang Hong, in 1986, at a depth of 10-16 m and a silt-clay sediment.
Specimens of Parodontophora wuleidaowanensis sp. nov. were collected from the inlet channel of the shrimp cultural ground at Wuleidao Bay (36u559N, 122u009E) in the Yellow Sea on 23 April 1992. Two specimens were also collected from the branchiae of adult female shrimps cultured at the breeding pond. The environmental features of Wulaeidao Bay and a description of the shrimp culture ponds were given by Zhang et al. (1994).
Specimens were fixed in 5% formalin in seawater, mounted in anhydrous glycerin with coverslip supports and measured using light microscopy (Olympus BHS equipped with differential interference contrast facility). All drawings were made using a drawing tube.
The formulae used for the dimensions are as described in Platt and Zhang (1982) and Zhang (1992). Abbreviations are as follows: a, body length/max. body diameter; a.b.d., anal body diameter; b, body length/oesophagus length; c, body length/tail length; c.d., corresponding body diameter; Sc, spicule length as chord; V, vulva distance from the anterior end of body.
Type material is deposited in the Natural History Museum (London). More paratype male and female specimens are also available in the College of Life Marine Science in the Ocean University of China, Qingdao, China.

Measurements
Measurements are given in Table I Cephalic setae in one circle, 9.4 mm (9-11 mm) in male and 10.5 mm (9-12 mm) in females (about 61.4% and 65.6% of head diameter). The buccal cavity is a prominent rounded cup shape with three indistinct weakly sclerotized tooth-like cusps. Amphids indistinct, 5.1 mm in width (5-6 mm, 31% of c.d.) in male and 6.5 mm in width (6-7 mm, 37.6% of c.d.) in female. Amphids 6.8-7.3 mm from the anterior. Groups of three lateral cervical setae 56.9¡5.0 mm from anterior in male and 54.3¡7.8 mm in female. Excretory pore situated on a seta-like projection of the cuticle, 22.6¡1.6 mm from anterior in male and 25.3¡4.0 mm in female. Nerve ring situated at 48.9¡2.2% of oesophagus length in Females. Two reflexed ovaries, the length of anterior one 362-382 mm and the posterior one 350-380 mm. Vulva situated at the 52.3¡6.4% of total length.

Discussion
The genus Paranticoma was established by Micoletzky and Kreis (1930) with the type species P. bandaensis. This genus can be distinguished from the closest genus Anticoma by the cup-shaped buccal cavity, excretory pore situated on a seta-like projection of the cuticle, single testis and supplementary organ reduced or vestigial. So far six species have been descrihed by Micoletzky and Kreis (1930), Wieser (1953), Mawson (1956), and Inglis (1967), respectively. All of these species are close to each other and can be distinguished by the structure of the spicules, the presence or absence of cervical setae and the relative position of such setae to the excretory pore, when present.

Etymology
Parodontophora deltensis is named for its typical habitat, the submarine delta of the Huanghe River Estuary and adjacent Laizhou Bay.

Measurements
Measurements are given in Table II

Description
Cuticle with faint outer striation discernible in the lateral field. Six outer labial papillae around the lip region. Cephalic setae 4.2 mm long, 4.2-5.0 mm from the anterior end. Cervical setae 3 mm long, arranged as two subdorsal groups of two longitudinally arranged setae and two subventral (or single) setae, i.e. (2D-2V)2 or (2D-1V)2 for most individuals. Somatic setae scattered. There are five pairs of subventral setae on the conical portion of the tail and several irregular short setae on the cylindrical part of the tail. The mouth opens into a short vestibulum which links the stoma, consisting of a slightly conical anterior part and a cylindrical posterior part with highly cuticularized walls, equal in thickness, 23-25 mm long and 4-5 mm wide. There are six bifurcate teeth at the tip of the cylindrical stoma. Buccal cavity about 27-33 mm long from tip of teeth to the base of stoma. Oesophagus starting at the base of the stoma, widens gradually to the base and forms a bulb in the last fifth of oesophageal length (not illustrated in Figure 2). Amphid semi-looped with the shorter dorsal branch and parallel much longer ventral branch surpassing the base of the stoma. Generally, length of the dorsal branch equals about 0.45 of ventral length (0.36-0.55) and the amphid length is about 1.16 times the buccal cavity length (1.0-1.27 times). The renette cell is elongated oval or rectangular, 61 mm long (49-71 mm), about 0.37 of the oesophageal length (0.27-0.44), situated just behind the small conoid cardia. Nerve ring at the level of about 0.63 of the oesophageal length (0.58-0.67). Excretory pore indistinct at the middle level of buccal cavity.

Differential diagnosis
Parodontophora deltensis sp. nov. is characterized by the position of the posterior end of the amphid extending slightly beyond the base of the stoma (1.0-1.3 times the length of the buccal cavity). Slightly irregular cervical setae arranged as (2D-2V)2 for most males, females and all juveniles, with some exceptions (2D-1V)2 for a small number of males and (3D-1V)2 for some females. Parodontophora deltensis sp. nov. is close to P. paragranulifera (Timm, 1952) in the length of the amphid, with the ventral branch extending past the base of the stoma. However, P. delteusis sp. nov. may be separated from that species by the irregularly arranged cervical setae, (2D-2V)2 for the most males, females and juveniles, with some exceptions arranged as (2D-1V)2 for several males and (3D-1V)2 for some females. Cervical setae are arranged more irregularly in P. paragranulifera. The new species differs also from P. paragranulifera in the ratio of length of dorsal branch to ventral branch (0.36-0.55 versus 0.20-0.25) and anterior one-third of ventral branch running parallel to the dorsal branch, not looping.

Discussion
The genus Parodontophora was erected by Timm (1963) for Odontophora species with parallel rather than conical walls of the stoma. Parodontophora paragranulifera (Timm, 1952) was chosen as the type species and many other species of Odontophora and Pseudolella were also included in this genus. Boucher (1973), Zhang (1991), and Smolyanko and Belogurov (1995) constructed a dichotomous and tabular key to the species, based on the following characters: length of ventral branch of amphids, position of the excretory pore from the anterior end, the arrangement of cervical setae, relative length of renette cell and presence or absence of armilliths in the endocapola, which was described as one stomatoidal ring in Paradontophora repens (Smolyanko and Belogurov 1995), but it was not found in our specimens. So far 17 species are known in the genus including P. limnophila (Wu et al. 2000), the only species found in freshwater habitats, and the present two new species, P. deltensis sp. nov and P. wuleidaowanensis sp. nov.

Type material
Holotype: one male. Paratypes: two males, two females.

Type locality and habitat
Wuleidaowan Yellow Sea, 119u599010E, 36u589000N, water depth 1 m, silt-clay, two males and one female; one male and one female collected from the branchial filaments of mature female prawn Penaeus (Fenneropenaeus) chinensis (Osbeck), in the spawning pond, 25 April 1992.

Etymology
Parodontophora waleidaowanensis is named after the sea area where the specimens were collected.

Measurements
Measurements are given in Table III

Description
Body cylindrical, tapering toward extremeties. Cuticle with faint outer striation discernible in the lateral field. Six outer labial papillae around the lip region. Cephalic setae 4.0-5.0 mm long, 3.0-5.0 mm from the anterior end. Cervical setae 3 mm long, arranged as two subdorsal groups of two longitudinally arranged setae and single subventral seta, i.e. cervical seta formula: (2D-1V)2 both for males and females. There are irregular sublateral setae 3 mm long in the oesophageal region. Somatic setae scattered. There are six pairs of subventral setae on the conical portion of the tail and several irregular short setae on the cylindrical part of the tail. The mouth opens into a short vestibulum which links with the stoma, which has a slightly conical anterior part and a long posterior part with parallel highly cuticularized walls, equal in thickness, 21-25 mm long and 5.5-6.0 mm wide. There are six bifurcate teeth at the tip of the cylindrical stoma. Buccal cavity about 28.5-34 mm long from tip of teeth to the base of stoma. Oesophagus starting at the base of the stoma, widens gradually to the base and forms a bulb in the last quarter of oesophageal length. Amphids shaped like a shepherd's crook, with a short dorsal arm, 8-10 mm, and a much longer ventral arm extending past the stoma, 72-106 mm long. Amphid length about 2.53-3.12 times length of the buccal cavity. The renette cell is a long-oval 84-94 mm long, about 0.41-0.63 of the oesophageal length, just behind the small round cardia. Nerve ring is at 0.58-0.62 of the oesophageal length from the anterior. Excretory pore at middle level of the buccal cavity. Tail shape similar in both sexes, with the first half conical and the other half cylindrical. Three caudal gland cells open to the spinneret.
Males. Slightly smaller than females on average. Testes opposed and outstretched. Anterior testis to the right and posterior one to the left of the intestine. Spicules paired, arched with rounded proximal end and a slightly swollen sub-proximal part, about 9-10 mm from the proximal end. Spicules 39-49 mm long (arc). Gubernaculum with dorso-caudal directed apophysis 14 mm long, with the middle of its ventral side thickened. Caudal setae six pairs subventrally and a few unpaired dorsally.
Females. Two ovaries outstretched. Anterior ovary 398 mm long to the right and posterior one 368 mm long to the left of the intestine. Vulva slightly anterior to the mid-body. A pair of vulval glands present. Amphid ventral arm widens in the middle part, 4.5-5.5 mm wide, with fine striation. A few irregular setae on the tail.

Differential diagnosis
Parodontophora wuleidaowanensis sp. nov. may be separated from the close species P. danka Belogurov and Kartavtseva, 1975, by regularly arranged cervical setae (2D-1V)2 in both males and females (no description of cervical setae in P. danka), much longer amphid, ventral arm 72-106 mm versus 59 mm, about 2.5-3.1 times versus 2.0 times the length of buccal cavity, and the distinct structure of the proximal ends of the spicules with no invaginated hole in the present new species.

Discussion
Since the establishment of the genus Parodontophora by Timm (1963), a total of 18 species are known in the genus, including the present two new species, P. deltensis and P. wuleidaowanensis. Among them there are six species in which the amphid length extends past the level of the base of the buccal cavity, which can be divided in to three groups: (1) amphids 1.1-1.5 times as long as buccal cavity, P. paragranulifera (Timm, 1952), P. deltensis sp. nov.; (2) amphids about two times as long as buccal cavity, P. danka (Belogurov and Kartavtseva, 1975); (3) amphids more than two and half times as long as buccal cavity, including P. cobbi (Timm, 1952), length of amphids 80-28 mm, buccal cavity 19-22 mm, P. polita (Gerlach, 1955), length of amphids 125-150 mm, buccal cavity 35 mm. Length of amphids 72-106 mm and buccal cavity 29-34 mm in P. wuleidaowanensis sp. nov. A tabular key to the species of this last group is given in Table IV.