Bendiella longicauda, Leduc, Daniel & Zhao, Zeng Qi, 2016

Leduc, Daniel & Zhao, Zeng Qi, 2016, Molecular characterisation of five nematode species (Chromadorida, Selachinematidae) from shelf and upper slope sediments off New Zealand, with description of three new species, Zootaxa 4132 (1), pp. 59-76 : 70-74

Bendiella longicauda n. sp.

( Figures 5 & 6 , Table 2 )

Diagnosis. Bendiella longicauda n. sp. is characterised by having a long body (length 2762 mm), two dorsosublateral rows of pores from midbody to level of cloaca, amphideal fovea with 4.5 turns, anterior portion of buccal cavity with three sets of five cuticularised rhabdions, each with two pairs of pointed projections at posterior extremity, except for central rhabdion of each set which bears two pairs of pointed projections and an additional central projection situated above the other four, rhabdions of posterior buccal cavity with numerous small denticles, spicules 2.1 cloacal body diameters long, tail 13.3 cloacal body diameters long, conicocylindrical, and with conical portion 8% of tail length.

Etymology. The species name is derived from the Latin longus (= long) and cauda (= tail), and refers to the length of the tail.

Material examined. Holotype male ( NIWA 99781), collected 10 May 2015 ( NIWA cruise TAN 1506, station 45), continental shelf off Hauraki coast, New Zealand (175.1495º E, 35.8243º S); water depth: 127 m.

Description. Male Body cylindrical. Cuticle with transverse rows of punctations, lateral differentiation beginning at one third of pharynx length from anterior extremity, consisting of three longitudinal rows of more widely spaced, larger punctations, gradually decreasing in size posteriorly from level of cloaca. Somatic setae short and sparse, 2 µm long, situated on either side of cuticle lateral differentiation ( Fig. 6 C). Two dorsosublateral rows of pores visible from midbody to slightly posterior to level of cloaca ( Figs. 5 E & 6C). Head rounded, not set off. Six minute inner labial papillae; six small outer labial setae situated in same circle as four cephalic setae of similar length. Amphideal fovea multispiral with 4.5 turns, situated ~0.4 cbd from anterior extremity. Buccal cavity large, divided into anterior (cheilostom) and posterior portions (pharyngostom). Anterior portion of buccal cavity cylindrical to barrel-shaped, with three sets of five cuticularised rhabdions; each with two pairs or pointed projections at posterior extremity, except for central rhabdion of each set which bears two pairs of pointed projections and an additional central projection situated above the other four ( Fig. 5 E). Posterior buccal cavity narrower, surrounded by three Y-shaped pairs of rhabdions fused from two thirds of distance from anterior end; posterior rhabdions with numerous small denticles near anterior extremity ( Fig. 5 E). Pharynx cylindrical, muscular, without anterior or posterior bulb. Nerve ring at ~40% of pharynx length from anterior. Secretory-excretory system not observed.

Reproductive system diorchic with short, outstretched testes. Anterior testis on right of intestine, posterior testis on left of intestine; mature sperm cells round or globular, larger in anterior testis (11–13 × 23–27 mm) than posterior testis (8–9 × 8–9 mm). Spicules paired, 2.1 cloacal body diameters long, curved, tapering distally. Gubernaculum consisting of two detached lateral pieces (crurae) tapering distally; median portion of gubernaculum (corpus and cuneus) apparently absent. Four ventral setae present immediately anterior to cloaca; precloacal supplements absent. Tail long, conicocylindrical; conical portion short, 8% of tail length, with few, sparse setae. Caudal glands not observed.

Differential diagnosis. Bendiella longicauda n. sp. can be differentiated from the only other species of the genus, B. thalassa Leduc, 2013 , by the larger body size (2762 vs 975–1118 mm), higher value of a (38 vs 28–34), presence of cuticle pores (absent in B. thalassa ), fewer amphid turns (4.5 vs 5.25), presence of denticles on posterior rhabdions (vs no denticles in B. thalassa ), longer spicules (2.1 vs 1.4 cloacal body diameters), dimorphism in sperm size between anterior and posterior testes (no dimorphism in B. thalassa ), and longer tail (13.3 vs 7.0 cloacal body diameters).

Molecular sequence data. The SSU and D2–D3 of LSU phylogenetic trees comprised 15 and 11 sequences, respectively ( Figs 7 & 8 ). In the SSU tree, Cheironchus haurakiensis n. sp. was the most divergent sequence and was placed well away from the other two Cheironchus sequences. This degree of divergence among Cheironchus sequences is somewhat surprising given the close morphological similarities among species of this genus, however it is not possible to ascertain the identity of the other Cheironchus sequences due to lack of vouchers ( Armenteros et al. 2014). In the D2–D3 of LSU tree, Cheironchus haurakiensis n. sp. was placed in a clade together with Choanolaimus and Latronema (subfamily Choniolaiminae) and well away from Pseudocheironchus and Synonchiella (Selachinematinae) . Pseudocheironchus ingluviosus and Synonchiella rotundicauda appear to be relatively closely related (89% posterior probability support in D2–D3 of LSU tree), although the genus Synonchiella is polyphyletic according to the SSU tree. These data do not support the monophyly of the two selachinematid subfamilies, which is consistent with the findings of Leduc & Zhao (2015).

Analyses of SSU and D2–D3 of LSU sequences suggest a close relationship between Halichoanolaimus anisospermus n. sp. and Bendiella longicauda n. sp. (100% posterior probability support in the D2–D3 of LSU tree), consistent with the close morphological similarities between the two genera. In the SSU tree, Bendiella longicauda n. sp. differed from Halichoanolaimus dolichurus by 1% (12 in 850 base pairs including zero gap). In the D2–D3 of LSU tree, Bendiella longicauda n. sp. differed from Halichoanolaimus anisospermus n. sp. by 29% (141 in 747 base pairs including 28 gaps).

The sequences provided herein are the first sequences obtained from beyond subtidal depths for the Selachinematidae . Our preliminary analyses do not provide evidence of clustering according to depth (intertidal/ subtidal vs shelf/upper slope) or geographical location ( New Zealand vs Northern Hemisphere). The number of available Selachinematidae sequences, however, remains limited and comprehensive analyses based on a larger number of sequences will be necessary to provide more solid conclusions.

Figures

FIGURE 5. Bendiella longicauda n. sp. Male. A: Anterior body region; B: head; C: entire male; D: buccal armature; E: cloacal region. Scale bar: A = 70 mm, B = 35 mm, C = 310 mm, D = 16 mm, E = 38 mm.

FIGURE 6. Bendiella longicauda n. sp. Scanning electron micrographs of juveniles. A: Lateral view of cuticle in anterior body region; B: posterior body region (viewed from left-hand side); C: lateral view of cuticle in posterior body region (viewed from left-hand side). Scale bar: A = 20 mm, B = 75 mm, C = 25 mm.

FIGURE 7. Bayesian tree inferred from SSU sequences under the general time reversible (GTR) + proportion of invariable sites (I) + gamma distribution (G) model. Posterior probabilities greater than or equal to 50 % are given on appropriate clades. New sequences provided in the present study are shown in bold. The scale (bottom left) stands for substitutions per site.

FIGURE 8. Bayesian tree inferred from D 2 – D 3 of LSU sequences under the general time-reversible (GTR) + proportion of invariable sites (I) + gamma distribution (G) model. Posterior probabilities greater than or equal to 50 % are given on appropriate clades. New sequences provided in the present study are shown in bold. The scale (bottom left) stands for substitutions per site.