Two new species of Lauratonema (Nematoda: Lauratonematidae) from the intertidal zone of the East China Sea

Two new species of free-living marine nematodes of the genus Lauratonema Gerlach, 1953 from an intertidal sandy beach of the East China Sea are described and illustrated. Lauratonema macrostoma sp. nov. is characterized by a spacious buccal cavity, depth 2.1–2.3 times width; cup-shaped amphids; small blade-like spicules (14–16 µm long, 0.55–0.65 anal or cloacal body diameter [a.b.d.]) and unequal length of outer labial setae and cephalic setae (13–17 µm and 9–12 µm respectively). Lauratonema dongshanense sp. nov. can be distinguished by the small buccal cavity with a strong cuticularized transverse strip structure; cup-shaped amphids; small blade-like spicules (14–15 µm long, 0.58–0.67 a.b.d.), unequal length of outer labial setae and cephalic setae (8–10 µm and 5–7 µm respectively); the presence of a small precloacal papilla. A dichotomous key for the genus Lauratonema is given. http://zoobank.org/urn:lsid:zoobank.org:pub:B5BA6C15-E72A-4C62-97B4-1823E71A9355


Introduction
Meiofauna from a sandy beach of Fujian province, East China Sea has been studied over the past few years, for biomonitoring assessment of water quality in intertidal ecosystems. Meiofaunal sediments were collected on Dongshan Island in Zhangzhou City, Fujian Province, East China Sea in July 2012 during this research. Average abundance of meiofauna was 1272 ± 519 ind 10 cm -2 , with 60% of the specimens being free-living nematodes. The nematode fauna of this investigated site is dominated by the families Lauratonematidae, Xyalidae, Thoracostomopsidae and Ironidae, of which the abundance of the genus Lauratonema Gerlach, 1953 accounts for 24.19%. The present paper describes two new species of free-living marine nematodes belonging to the genus Lauratonema Gerlach, 1953. The genus Lauratonema was erected by Gerlach in 1953 with the type species L. reductum, for which he erected the family Lauratonematidae (Gerlach 1953;Gerlach and Riemann 1974). The most significant characteristic of Lauratonema is that the female genital duct is united with the rectum forming a cloaca (Gourbault and Vincx 1986;Keppner and Tarjan 1989). The taxonomy of Lauratonematidae is still in a state of flux and remains subject to debate (De Coninck 1965;Tchesunov 1984;Gourbault and Vincx 1986;Fadeeva 1989). Some authors (Clark 1961;De Coninck 1965;Andrássy 1976;Tchesunov 1984;Gourbault and Vincx 1986;Fadeeva 1989) put it in the order Enoplida, while Lorenzen (1981) transferred it to the order Trefusiida. Species and genera in this family have been comprehensively revised by De Coninck (1965) and Tchesunov (1984). De Coninck (1965 moved Lauratonema originale to Lauratonemoides, Tchesunov (1984) transfered Lauratonema minutum to Lauratonemoides and established the genus Lauratonemella solely for Lauratonema spiculifer Gerlach, 1959(De Coninck 1965Tchesunov 1984).

Materials and methods
Sediment samples were taken from an intertidal area on the coast of Dongshan Island in Zhangzhou City, Fujian Province, East China Sea, using a sawn-off syringe with a 2.9 cm inner diameter pushed into the sediment to a depth of 10 cm. Samples were taken at high, mid and low tide levels. Samples were fixed with 5% formalin in filtered seawater, then stained with 0.1% rose Bengal for more than 24 hours. The meiofauna were extracted from the sediment by decantation and/or Ludox centrifugation (Higgins and Thiel 1988). Each sample was washed into a lined Petri dish through two sieves (mesh sizes 500 and 31 µm) and the meiofauna was sorted to higher taxonomic levels under a stereoscopic microscope. Nematodes were transferred into a solution containing, by volume, 5% glycerol, 5% pure ethanol, and 90% freshwater in a cavity block to let the ethanol slowly evaporate and then mounted in glycerol on permanent slides (McIntyre and Warwick 1984). The descriptions were made from glycerine mounts using differential interference contrast microscopy (NIKON 80i, Tokyo, Japan). Drawings were made with a camera lucida. Types are deposited in the Institute of Oceanology, Chinese Academy of Sciences.
Measurements are in µm. Abbreviations are as follows: a, body length/maximum body diameter; b, body length/pharynx length; c, body length/tail length; a.b.d., anal or cloacal body diameter; c′, tail length/a.b.d.; c.b.d., corresponding body diameter; Sc, spicule length as arc.

Etymology
This species is named for its large buccal cavity.
Measurements (Table 1)  Description Body cylindrical, slightly tapering towards both extremities. Cuticle marked with fine and conspicuous striations, which reach base of cephalic setae, and with rod-shaped bacteria more or less adhered. Inner labial sensilla not visible. Six outer labial setae and four cephalic setae in one ring, length 13-17 µm and 9-12 µm respectively, situated at the level of about two-thirds of the buccal cavity depth. Spacious barrelshaped buccal cavity with strong cuticularized wall, depth 2.1-2.3 times width, slightly constricted at half its depth. Amphids unclear in some specimens, while obviously cup-shaped in others, located immediately posteriorly of the lateral outer labial setae, diameter about one-third of corresponding body diameter. Corresponding body diameter at posterior extremity of pharynx is 26-30 µm. Сardia large, nearly heart-shaped, surrounded by intestinal tissue. Nerve ring encircled pharynx at about 42-47% of its length. Excretory pore opening ventrally 77-91 µm from anterior end, 49-65 µm in front of nerve ring. Ventral gland small, situated about 40 µm anterior to end of pharynx. Tail elongate conoid, 4.6-5.7 a.b.d. long. Caudal glands well developed. Terminal seta absent. Spinneret small, terminal.
Male. Reproductive system diorchic with two testes arranged in tandem; anterior testis situated to right, posterior testis to left of the intestine. Spicules symmetrical and Female. Similar to male in general characteristics, but tail without ventrosublateral seta. Reproductive system monodelphic, reflexed, singlе ovary situatеd еntirеly to right of intestine. Gеnital zonе of oogonia arrangеd in onе or two rows; growth zonе with a singlе row of gradually enlarging ooсytе. Female genital duct united with rectum forming a cloaca.
Diagnosis and discussion Lauratonema macrostoma sp. nov. is characterized by the size of the buccal cavity and spicules, the shape of the amphids and the length of the cephalic setae. It is close to L. mentulatum Wieser, 1959 andL. reniamphidum Hopper, 1961, which also have buccal cavity longer than wide. However, several differences can be seen.

Etymology
This species is named for the type locality, intertidal sediment on Dongshan Island.

Description
Body elongated and attenuating towards the ends. Cuticle marked with fine and prominent transverse striations from posterior border of amphids to tip of tail and with rod-shaped bacteria more or less adhered. Inner labial sensilla not seen. Six outer labial setae and four cephalic setae in single crown, length 8-10 µm and 5-7 µm respectively, situated 8-10 µm posterior to anterior end. Funnel-shaped buccal cavity with strong cuticularized transverse strip structure, depth almost equal to width. Amphids cup-shaped, situated just posterior to the lateral outer labial setae, with diameter 0.32-0.44 times of corresponding body diameter. Pharynx cylindrical and musсular, with corresponding body diameter 23-31 µm at posterior extremity. Сardia large, nearly heart-shaped, surrounded by intestinal tissue. Nerve ring surrounding pharynx situated at 47-51% of its length. Excretory duct very short, excretory pore situated 54-73 µm anterior to nerve ring, ventral gland located at 40-50 µm anterior to end of pharynx. Caudal glands well developed. Terminal seta absent.
Male. Tail elongate conoid, length 123-126 µm, 5.3-5.6 a.b.d. long. Two rows of setae just located at ventrosublateral of tail. Reproductive system diorchic with two testes arranged in tandem; anterior testis situated to right, posterior testis to left of intestine. Spicules blade-like, short and straight, 0.58-0.67 times a.b.d. long. In three measured specimens, one with spicules with proximal end unclosed ( Figure 3F), others with slightly cephalated proximal end ( Figure 3E). No gubernaculum observed. A small papilla situated at about 15 µm anterior to cloaca.
Female. Similar to male in general characteristics, but tail a little longer, length 137-141 µm, without ventrosublateral seta. Reproductive system monodelphic, single ovary reflexed, situatеd entirely to right of intestine. Gеnital zonе of oogonia arrangеd in onе or two rows; growth zonе with a singlе row of gradually enlarging ooсytеs. Female genital duct united with rectum forming a cloaca. Diagnosis and discussion Lauratonema dongshanense sp. nov. is morphologically close to L. pugiunculus Wieser, 1959, L. reductum Gerlach, 1953and L. hospitum Gerlach, 1954 in several characteristics, such as their small buccal cavities, which are as short as or shorter than wide; outer labial setae and cephalic setae of unequal length; gubernaculum absent. However, the new species can be easily distinguished by the shape of buccal cavity (funnel-shaped with strong cuticularized transverse strip structure, depth almost equal to width versus small and conical) and spicules (blade-like, short and straight versus slender, more or less straight but with an S-like bend), the number and arrangement of male caudal papillae (one small precloacal ventral papilla versus three to four postcloacal ventral papillae), the tail length (c 10.  Hopper (1961), and three new species were described later: L. obtusicaudatum Murphy andJensen, 1961, L. minutum Platonova, 1971 and L. juncta Fadeeva, 1989. However, L. originale was moved to Lauratonemoides by De Coninck (1965). Tchesunov (1984) gave a dichotomous key to the family Lauratonematidae, transferred Lauratonema minutum, the gonad of which is very similar to L. originalis, to Lauratonemoides, and established the genus Lauratonemella solely for L. spiculifer Gerlach, 1959(De Coninck 1965Tchesunov 1984;Gourbault and Vincx 1986;Fadeeva 1989). Therefore, this genus contains eight valid species. We revise the key base on Hopper (1961) and Tchesunov (1984) including all known eight valid species in this genus as well as the two newly described species, according to the size of buccal cavity, the shape and situation of the amphids, the length of the cephalic setae, the length and shape of spicules, the existence of ventral papillae, etc., as follows (Gerlach 1953(Gerlach , 1954Wieser 1959;Hopper 1961;Murphy and Jensen 1961;Tchesunov 1984;Fadeeva 1989).
Key to species of the genus Lauratonema