Two new free-living nematode species of Setosabatieria (Comesomatidea) from the East China Sea and the Chukchi Sea

Two new free-living marine nematode species of the genus Setosabatieria from the sandy intertidal zone of Xiamen, in the East China Sea and a shallow water area in the Chukchi Sea, Arctic Ocean are described and illustrated. Setosabatieria longiapophysis sp. nov. is characterized by four longitudinal files with 7–9 cervical setae per file, 15–16 minute papillate precloacal supplements and relatively long straight apophyses of gubernaculum. Setosabatieria major sp. nov. is identified by its relatively large body of 2701–3144 µm, the number (10–11) of cervical setae per file, 26–28 minute papillate precloacal supplements and spicules with a central septum at both the proximal and distal end. A pictorial identification key to all known species of Setosabatieria is provided. http://zoobank.org/urn:lsid:zoobank.org:pub:B8A2BEC9-5CD4-4AA9-9CA8-D1AE1FDE4887


Introduction
Setosabatieria was first erected by Platt (1985) to accommodate two Sabatieria species possessing synapomorphic features warranting recognition as a separate genus, namely the lack of cuticular punctations and the presence of four sublateral files of numerous long cervical setae (Platt 1985). To date, eight species of Setosabatieria with distinct differentiating morphology have been reported from oceans worldwide . Leduc et al. (2012) provided a dichotomous key to the genus based on tail shape, spicule shape, and the number of windings of amphidial fovea and precloacal supplements. Two new Setosabatieria species from the sandy intertidal zone of Xiamen in the East China Sea and a shallow water area in the Chukchi Sea, Arctic Ocean are described and illustrated in this paper.

Methods
Nematode samples from Xiamen, East China Sea were collected in October 2011 from the sandy intertidal zone at Guliang Island. Sediments from the Chukchi Sea, Arctic Ocean were collected using a multicorer during the Fourth Chinese National Arctic Research Expedition from July to September, 2010. The samples were fixed with 5% formalin in seawater. In the laboratory, the samples were stained with rose Bengal for more than 24 h. Nematodes were extracted from the sediment by decantation and/or Ludox centrifugation (Warwick et al. 1998). Each extracted sample was washed into a lined Petri dish and the meiofauna were sorted under a stereoscopic microscope to higher taxonomic levels. Nematodes were transferred into an embryo glass dish containing by volume 5% glycerine, 5% pure ethanol, 90% freshwater, and left in a desiccator for a few days. This allows the ethanol and water to evaporate slowly leaving the nematodes in pure glycerol. The descriptions have been made from glycerine mounts using interference contrast microscopy (NIKON 80i, Shizuoka, Japan). Drawings were made with the aid of a camera lucida. Type specimens are deposited in the Institute of Oceanology, Chinese Academy of Sciences.
Measurements are in µm. Abbreviations are as follows: a, total body length divided by maximum body diameter; b, total body length divided by pharynx length; c, total body length divided by tail length; a.b.d., anal body diameter; c′, tail length divided by a.b.d.; Spic, spicule length as chord; Tl, total body length; Hd, head diameter as percentage of body diameter at level posterior pharynx; A%, amphid diameter as percentage of corresponding body diameter; At, number of turns of amphidial fovea; R3, cephalic setae length as percentage of head diameter; Cs, number of cervical setae in each sublateral row; Ps, number of precloacal supplements; V%, position of vulva from anterior as percentage of total body length.

Etymology
This species is named for the long straight apophyses of gubernaculum.

Measurements
Measurements are given in Table 1. Description Body cylindrical, tapering towards both extremities, maximum body diameter 42-58 µm. Cuticle not punctate but with faint transverse striations visible throughout body. Head narrower than rest of body due to constriction at level of amphidial fovea. Buccal cavity cup-shaped. Inner labial sensilla not visible, outer labial sensilla setiform, 2 μm long. Four cephalic setae 16-19 µm long (100-120% of head diameter). Cervical setae, similar to cephalic setae length, arranged in four longitudinal files of seven to nine setae. Amphidial fovea spiral, with 2.75-3 turns, 15-17 µm in diameter, occupying 49-69% of corresponding body diameter. Pharynx gradually enlarging posteriorly but without true terminal bulb. Nerve ring at 61-65% of pharynx length from anterior end. Cardia small, muscular, surrounded by intestinal tissue. Excretory pore posterior to nerve ring. Tail conico-cylindrical, Females. Similar to male in general characteristics, but amphid diameter smaller; vulva at 49-50% of total body length but developed reproductive system not found.
Differential diagnosis Setosabatieria longiapophysis sp. nov. is similar to Setosabatieria triangularis Riera et al. 2006 in that they both have longer cephalic setae than in the other species, and a similar number of cervical setae in each sublateral row and precloacal supplements (Table 3). However, Setosabatieria longiapophysis sp. nov. has spicules with straight apophyses 31-37 µm long in contrast to the triangular apophyses of S. triangularis.

Type locality and habitat
Sublittoral zone in the Chukchi Sea (the Arctic Ocean). Latitude: 68.1336°N, longitude: 167.8633°W.

Etymology
This species is named for the large body.

Measurements
Measurements are given in Table 2.

Males.
Reproductive system with two opposite outstretched testes. Spicules paired, equal, slight arcuate, 0.9-1.3 times as long as cloacal body diameter, with central septum appearing in both proximal and distal portions. Gubernaculum with a pair of short dorsocaudal apophyses. There are 26-28 small pre-cloacal papillae supplements, although they are very small and difficult to observe.
Females. Similar to male in general characteristics, but tail with fewer short setae and narrow cylindrical posterior portion longer than anterior conical portion. Reproductive system with two outstretched equally developed ovaries. Vulva at 44% of total body length.

Differential diagnosis
Setosabatieria major sp. nov. is characterized by its rather large body (length 2700-3145 µm; maximum body diameter 106-176 µm), the number (10-11) of cervical setae per file, 26-28 small papillate precloacal supplements and central septum appearing in both proximal and distal portions of spicules. These characters are obviously different from those of other species in this genus.

Discussion
Setosabatieria longiapophysis sp. nov. was found in the samples from low tidal level where 38% of the specimens were free-living nematodes, It accounted for 1% of the total number of nematodes. Setosabatieria major sp. nov. was found in subsurface sediments at 2-4 cm depth. It accounted for 3% of total nematode abundance at the type locality CC4 station (Lin et al. 2014). At present, the three species of Setosabatieria found in China are distributed in three distant sea areas: Bohai, the Yellow Sea and the East China Sea. The geographic distributions of other valid species in the genus are given by  and Platt (1985). The genus has a worldwide distribution. The dichotomous keys including seven species in this genus were provided by Leduc et al. (2012). Composite differentiating characters of all known male Setosabatieria species are provided as an aid to identification (Table 3). Based on , the pictorial key of the genus is shown in Figure 5.