Litinium gludi, Leduc & Zhao, 2021

Leduc, Daniel & Zhao, Zeng Qi, 2021, Litinium gludi sp. nov. (Nematoda, Oxystominidae) from Kermadec Trench, Southwest Pacific Ocean, European Journal of Taxonomy 748 (1), pp. 138-154 : 143-151

Litinium gludi sp. nov.

urn:lsid:zoobank.org:act:FA79DFEF-A389-48AA-AF75-03984D69F202

Figs 1–4 , Table 1

Diagnosis

Litinium gludi sp. nov. is characterised by a slender body (a = 58–63), a body length of 895–1066 µm, papilliform labial sensilla, short cephalic sensilla 1.5–2.0 µm or ~0.2 cbd long, a large heart- or leafshaped amphideal fovea 67–88% cbd wide, a smaller amphideal aperture with two central longitudinal ridges, males with dimorphic sperm, spicules 1.1–1.4 times cloacal body diameter, a short and simple gubernaculum, and two precloacal setae.

Differential diagnosis

The new species resembles L. aceratus and L. longicaudatus , the only other species of the genus with conico-cylindrical tails, and is particularly similar to L. longicaudataus in having papillose (<2 µm) labial sensilla. Litinium gludi sp. nov. can be differentiated from L. longicaudatus by the shorter body (895–1066 vs 2180–2196 µm in L. longicaudatus ), lower ‘a’ ratio (58–63 vs 75–86), and heart- or leafshaped amphideal fovea (vs pocket-shaped).

Etymology

The species is named after Professor Ronnie Glud, leader of the HADES-ERC trench project and covoyage leader.

Material examined

Holotype PACIFIC OCEAN • ♂; Kermadec Trench , voyage TAN1711, station 25, site 3; 30.3815° S, 176.6417° W; 9540 m water depth, 0–2 cm sediment depth; 3 Dec. 2017; NIWA 139257 .

Paratypes PACIFIC OCEAN • 2 ♂♂, 1 ♀; Kermadec Trench , voyage TAN1711, station 25, site 3; 30.3815° S, 176.6417° W; 9540 m water depth, 0–2 cm sediment depth; 3 Dec. 2017; NIWA 139258 .

Description

Males

Body slender, cylindrical, widest at level of nerve ring, tapering slightly towards anterior extremity. Cuticle smooth, without ornamentation; somatic setae absent, except for sparse sublateral setae on tail. Cephalic region demarcated by slight constriction near posterior edge of amphideal fovea. Inner labial sensilla not observed; six outer labial papillae, ~ 0.5 µm long, located slightly anterior to amphideal fovea and four short cephalic sensilla, 1.5–2.0 µm or ~0.2 cbd long, situated far posteriorly at level of posterior edge of amphideal fovea. Amphideal fovea large, heart- or drop-shaped, with lightly cuticularized outline; amphideal aperture smaller, oval- or drop shaped, with two lightly cuticularized longitudinal central ridges spanning long axis of amphideal fovea. Buccal cavity narrow, cylindrical, with cuticularized portion 3–5 µm deep. Pharynx muscular, cylindrical, surrounding posterior portion of buccal cavity, widening towards posterior extremity but not forming true bulb. Nerve ring located slightly anterior to middle of pharynx. Secretory-excretory system not observed. Cardia 2–4 µm long, partially embedded in intestine.

Reproductive system with two opposed and outstretched testes; anterior testis located to the left or right of intestine, posterior testis located on opposite side or on same side. Mature sperm in anterior testis large, elongated, 19–21 × 2–3 µm; mature sperm in posterior testis smaller, globular, 1.5 × 1.5–2.0 µm. Spicules short, 1.1–1.4 times cloacal body diameter, curved distally, with ventrally bent capitulum. Gubernaculum small, simple, block-shaped, without lateral pieces, with poorly developed apophyses. Two precloacal papillae, 1.3–1.4 µm long; posterior-most papilla located 11–14 µm anterior to cloaca, second precloacal papilla located 19–22 µm from posterior-most precloacal papilla. Ejaculatory glands not observed. Tail conico-cylindrical, with pointed tip, caudal capsule absent; three caudal glands present posterior to cloaca; spinneret not observed.

Female

Similar to males but without any somatic setae on tail. Reproductive system with single posterior genital branch and reflexed ovary. Oocyte up to 160 × 10 µm. Vulva located far anteriorly at about ⅓ of body length from anterior extremity. Vagina perpendicular to body surface; vaginal glands not observed.

Molecular phylogenetic relationships

Near full-length SSU (1516 bp) and D2-D3 of LSU sequences (756 bp) were obtained for Litinium gludi sp. nov. The Oxystominidae did not form a monophyletic clade in the consensus SSU tree due to the placement of Rhaptothyerus typicus Hope & Murphy, 1969 and oncholaimoid sequences among the oxystominid sequences ( Fig. 5 ). Neither the Halalaiminae (represented by Halalaimus and Oxystomina ) nor the Oxystomininae (all other oxystominid genera) were recovered as monophyletic. Litinium gludi sp. nov. was placed in a well-supported clade (100% posterior probability and 82% bootstrap support) with sequences of Thalassoalaimus . The similarity between SSU sequences of Litinium gludi sp. nov. and Thalassoalaimus sp. was 94–95% with a difference of 69 in 1508 nucleotides with 4 gaps ( MN250034 ), 83 in 1504 nucleotides with 1 gap ( HM564634 ) and 43 in 798 nucleotides with 1 gap ( MN250041 ). The Litinium gludi sp. nov. + Thalassoalaimus clade was part of a wider, strongly supported oxystominid clade including all sequences of Litinium and Cricohalalaimus (100% posterior probability and bootstrap support), although neither Litinium nor Thalassoalaimus were monophyletic. The similarity between SSU sequences of Litinium gludi sp. nov. and Litinium sp. was 87–94% with a difference of 84 in 1513 nucleotides with 5 gaps ( FJ040500 ), 116 in 1516 nucleotides with 3 gaps ( HM564629 ), 113 in 1514 nucleotides with 2 gaps ( HM564649 ), and 46 in 786 nucleotides with 1 gap ( MK626773 ). Sequences of Halalaimus formed a strongly supported (100% posterior probability and bootstrap support) monophyletic sister group to the Oncholaimoidea Filipjev, 1916, the latter also forming a strongly supported monophyletic group (100% posterior probability and bootstrap support). The sequences of Oxystomina formed a strongly supported group (100% posterior probability and bootstrap support), however this genus was not monophyletic due to the inclusion of a sequence of Nemanema Cobb, 1920 in the clade. The placement of another sequence of Nemanema as a sister group to the Halalaimu s + Oncholaimoidea clade was poorly supported (56% posterior probability and <50% bootstrap support).

The topology of the D2-D3 of LSU consensus tree was similar to that of the SSU tree, with the Oxystominidae again not recovered as monophyletic ( Fig. 6 ). Sequences of Halalaimus and Oxystomina each formed strongly supported monophyletic clades (100% posterior probability and bootstrap support). As in the SSU tree, Litinium, Cricohalalaimus, and Thalassohalaimus formed a strongly supported clade (100% posterior probability and bootstrap support), with Litinium gludi sp. nov. most closely related to Thalassoalaimus (100% posterior probability and 98% bootstrap support). The similarity between LSU sequences of Litinium gludi sp. nov. and Thalassoalaimus sp. was 92% with a difference of 118 in 664 nucleotides with 7 gaps ( HM564880 ); the similarity between LSU sequences of Litinium gludi sp. nov. and Litinium sp. was 71–72% with a difference of 188 in 671 nucleotides with 13 gaps ( HM564858 ), 184 in 671 nucleotides with 12 gaps ( HM564874 ) and 183 in 671 nucleotides with 13 gaps ( HM564875 ).

Figures

Fig. 1. Litinium gludi sp. nov. A. Anterior body region of the male holotype (NIWA 139257).B. Cephalic region of the female paratype (NIWA 139258). C. Cephalic region of the male paratype (NIWA 139258). D. Posterior body region of the female paratype (NIWA 139258). E. Posterior body region of the male holotype (NIWA 139257). Scale bar: A = 65 µm, B–C = 15 µm, D–E = 25 µm.

Fig. 2. Litinium gludi sp. nov. A. Entire female paratype (NIWA 139258). B. Entire male holotype (NIWA 139257). Scale bar = 200 µm.

Fig. 3. Litinium gludi sp. nov., light micrographs of the male holotype (NIWA 139257). A. Surface view of cephalic region showing amphid and outer labial sensilla. B. Optical cross-section of cephalic region showing narrow buccal cavity and pharynx. C. Anterior testis showing elongated sperm cells (arrow). D. Posterior testis showing globular sperm cells (arrow). Scale bar = 10 µm.

Fig. 4. Litinium gludi sp. nov., light micrograph of tail tip of the male holotype (NIWA 139257), showing absence of caudal capsule and spinneret. Scale bar = 2 µm.

Fig. 5. Bayesian tree inferred from SSU sequences, aligned using the MUSCLE alignment algorithm under the general time-reversible (GTR) + I (proportion of invariable sites) + gamma distribution (G) model. The new sequence is shown in bold font on a grey background. Posterior probabilities (left) and bootstrap values (right) greater than or equal to 50% are given on appropriate clades. The scale stands for substitutions per site. -: less than 50% bootstrap support; #: sequence FJ040500 is labelled Thalassoalaimus pirum in GenBank but is labelled Litinium pirum here to reflect the new classification of this species proposed by Martelli et al. (2017).

Fig. 6. Bayesian tree inferred from D2-D3 of LSU sequences, aligned using the MUSCLE alignment algorithm under the general time-reversible (GTR) + I (proportion of invariable sites) + gamma distribution (G) model. Posterior probabilities (left) and bootstrap values (right) greater than or equal to 50% are given on appropriate clades. The new sequence is shown in bold font on a grey background. The scale stands for substitutions per site. *: no bootstrap support; -: less than 50% bootstrap support.