Three new species of the genus Belbolla (Nematoda: Enoplida: Enchelidiidae) from the Yellow Sea, China

Three new species of free‐living marine nematodes of the genus Belbolla: Belbolla huanghaiensis sp. nov., Belbolla stenocephalum sp. nov. and Belbolla warwicki sp. nov. from the Yellow Sea, China, are described and illustrated. Belbolla huanghaiensis can be separated from other species in the Belbolla genus by the number of oesophageal bulbs (nine), the length of the spicules and gubernacular apophysis, and the size of the two winged precloacal supplements. Belbolla stenocephalum can be separated from other species by the number of oesophageal bulbs (eight), the length of the spicules and the structure of gubernacular apophysis. Belbolla warwicki sp. nov. is characterized by the number of oesophageal bulbs (seven), reduced precloacal supplements and the structure of gubernacular apophysis. A key to the genus Belbolla is provided to facilitate species identification. Types are deposited in the College of Life Science and Technology, Ocean University of China.


Introduction
In January 2003, sediment samples were taken at 23 stations in the Yellow Sea, China. Meiofaunal abundance varied from 553 to 1400 individuals per 10 cm 2 (average 847¡254), with 81-93% (average 86%) of the specimens being nematodes. Up to now, 29 species of marine nematodes have been recorded from the Yellow Sea (Zhang and Platt 1983;Zhang and Ji 1994;Hope and Zhang 1995), but only one species of Belbolla, B. zhangi had been described from the Bohai Sea, China (Guo and Warwick 2001).
Belbolla is a genus of the family Enchelidiidae that belongs to the Enoplida. The name of the genus Belbolla was suggested by Andrássy (1973), instead of the previously used name Bolbella Cobb, 1920. It is probable that Andrássy's paper was not available when Gerlach and Riemann (1973/74) wrote the monographs and proposed to change the previously used name Bolbellia. The name Bolbellia was thus a recent synonym of that proposed by Andrássy. The type species of this genus is Belbolla tenuidens (Cobb, 1920) (Bolbella tenuidens Cobb, 1920); Bolbellia tenuidens (Gerlach and Riemann, 1974). So far, nine species of this genus have been recorded (Platt and Warwick 1983;Guo and Warwick 2001). But, the species of this genus from the Yellow Sea, China have not been studied in the past. We found three species of this genus by investigation and study in the Yellow Sea, and all three species are new. In this paper we describe the three new species.

Material and methods
Undisturbed sediment samples were taken using a 0.1 m 2 improved Gray-O'Hara box corer, and meiofauna samples were taken using a sawn-off syringe tube with a 2.6 cm inner diameter, pushed into the sediment down to 8 cm depth whilst withdrawing the plunger to avoid core compression. Samples were stratified by 0-2, 2-5, 5-8 cm and each fixed with 5% formalin in seawater. In the laboratory, the samples were stained with rose Bengal for more than 24 h. Then all the samples were washed on a 50 mm sieve for the lower size limit and a 0.5 mm sieve for the upper size limit to remove the formalin. Ludox-TM was used to extract meiofauna from sediment by centrifugation. Each sample was washed into a lined Petri dish and the meiofauna was sorted under a stereoscopic microscope to higher taxonomic levels. Nematodes were transferred into 9:1 (v/v) solution of 50% alcohol-glycerol in an embryo dish to slowly evaporate to pure glycerol, then mounted on to a permanent slide. The descriptions have been made from glycerine mounts using interference contrast microscopy. Drawings were made with the aid of a camera lucida. Morphometic data are presented using the modification of Filipjev's standard formula described by Platt (1973

Etymology
This species is named after the Yellow Sea.

Measurements
Measurements are given in Table I.

Description
The body size of the species is relatively large for this genus. Furthermore, the male size is markedly larger than the female; they average 3382 mm long and 87 mm wide. The anterior end of the body tapers to a very small diameter. The buccal cavity has a large right ventrolateral tooth and two less prominent teeth (dorsal and left ventro-lateral in position). The cuticular ring separating the two buccal chambers is smooth (i.e. with no denticles). The mouth is surrounded by six small papillae and there are 10 cephalic setae (10-13 mm long) arranged in one circle. There are dozens of cervical setae. The anterior 10 cervical setae (18-26 mm long) are in one circle (about 26 mm from head end), and the others are arranged irregularly. The oesophagus expands gradually and evenly and is modified into nine bulbs that are regarded as characteristic of the genus. Nerve ring at 41-46% oesophagus length. Spicules 106-137 mm (1.9-2.1 a.b.d.) as arc, 70-81 mm as long chord, curved with a tapered distal tip. Gubernaculum with long dorso-caudally directed apophysis, 45-60 mm long. Two winged precloacal supplements well developed. Tail 3.8-5.2 a.b.d., conico-cylindrical, tapering, with the distal third cylindrical and with a slightly swollen tip.
Males. Tail relatively stout over most of its length, narrowing rather sharply in the posterior one-third. The spicules are equal in length and identical in structure with round, blunt proximal ends, and a tapered distal tip. The gubernaculum has a pair of 45-60 mm apophyses, longer than half the length of spicule. The two pre-cloacal supplements

Differential diagnosis
Belbolla huanghaiensis sp. nov. is characterized by the numbers of oesophageal bulbs, the length of the spicules and gubernacular apophyses, and the size of the two winged precloacal supplements. It is close to B. californica Allgen, 1951, but differs by the length of spicules and gubernacular apophyses, and the distance of the posterior supplement from the proximal ends of the spicules. In species of B. huanghaiensis, both males and females have nine oesophageal bulbs, while for B. californica, females have 10 oesophageal bulbs. In the former, the spicule length as arc is longer than 100 mm; gubernacular apophysis is longer than 42 mm. The posterior supplements are distant from the proximal end of the spicule by more than one spicule length. In the latter, the length of the spicule is 68 mm; gubernacular apophysis is 21 mm. The posterior supplements are distant from the proximal end of the spicule by less than one spicule length. This species is close to B. zhangi Guo, 2001, but differs by the number of oesophageal bulbs and the size of the male body. In this species, the numbers of oesophageal bulbs of male, female and juvenile are all nine. The body size is relatively larger, and the male body (3037-3700 mm long, CV% 9.9) is markedly longer than that of the female. While in B. zhangi, the numbers of oesophageal bulbs vary between eight and nine. The body size is smaller, and the body lengths of males and females are nearly equal (2230-2750 mm long, CV% 9.0).

Etymology
This species is named after the feature of its body.

Measurements
Measurements are given in Table II.

Description
The anterior end of the body tapers to a very small diameter. The buccal cavity has a large right ventro-lateral tooth and two less prominent teeth (dorsal and left ventro-lateral in position), and is separated into two chambers by a smooth cuticular ring. The mouth is surrounded by six small papillae and there are 10 cephalic setae (9-12 mm long) arranged in one circle. There are dozens of cervical setae. The anterior 10 cervical setae (17-26 mm long) are in one circle (about 23 mm from head end), and the others are arranged irregularly.  Females. Body size longer in female than male, ovaries paired, equal, opposed, reflexed. Vulva at 48-50% of body length.

Differential diagnosis
Belbolla stenocephalum sp. nov. is characterized by the numbers of oesophageal bulbs, the structure of the spicules and and the length of the gubernacular apophyses. It is close to B. zhangi Guo, 2001, but differs by the structure of spicules and the length of the gubernacular apophyses. In this species, the numbers of oesophageal bulbs are eight in each individual, the spicule has a swollen distal tip. Length of the gubernacular apophysis is 34-36 mm, shorter than half the length of a spicule. In B. zhangi, the number of oesophageal bulbs is eight or nine, and the spicule has a tapered distal tip. Length of the gubernacular apophysis is 40-45 mm, longer than half the length of a spicule.

Type locality
Sublittoral in the Yellow Sea:

Etymology
This species is named in honour of Professor R. M. Warwick.

Measurements
Measurements are given in Table III.

Description
The body size of this species is relatively small compared to the other species of the genus, 1230-1690 mm long. The anterior end of the body tapers to a very small diameter. The buccal cavity has a large right ventro-lateral tooth and is separated into two chambers by a cuticular ring. There are 10 cephalic setae (5-6 mm long) arranged in one circle. There are dozens of cervical setae. The anterior 10 cervical setae (10-15 mm long) are in one circle (about 12 mm from head end), and the others are arranged irregularly. The oesophagus expands gradually and evenly and is modified into seven bulbs (first bulb sometimes not very clear in the males), which is regarded as characteristic of the genus. Oesophageal part is relatively short. Nerve ring 51-56% oesophageal length. Spicules 33-37 mm (1.3-2.5 Males. Tail relatively stout over most of its length and gradually narrowing and cylindrical in the posterior quarter. The spicules are equal in length and identical in structure with rounded, blunt proximal ends. The gubernaculum has a pair of 7.5-8.0 mm apophyses. The two pre-cloacal supplements are reduced, in long pocket-shaped structure, not winged shape, which is regarded as characteristic of the genus. Tail with three terminal setae.

Differential diagnosis
Belbolla warwicki sp. nov. is characterized by the number of oesophageal bulbs, the shape of the spicule, gubernacular apophysis and precloacal supplements. It is close to B. asupplementata Juario, 1974. They all have seven bulbs, but the principal difference between the species is the presence or absence of precloacal supplements and the shape, the size of spicules and gubernacular apophyses. In B. warwicki, precloacal supplements are present, whilst in B. asupplementata, precloacal supplements are absent. The body size and the shape of spicule and gubernacular are very different.

Discussion
The genus Belbolla is characterized by multiple oesophageal bulbs, and the number of bulbs is an important feature in classification (Belogurov and Belogurova 1980). So, we use this characteristic as the principal basis of identification. In the three new species, the numbers of oesophageal bulbs are invariable in every species. Most characters of the three new species show marked interspecific variation, and little intraspecific variation. So, we think that B. huanghaiensis, B. stenocephalum and B. warwick should be new species.