Metadasynemoides taihua, Leduc, 2024

Leduc, Daniel, 2024, Four new free-living marine nematode species (Plectida: Ceramonematidae) and two new species records (Desmodorida: Desmodorinae) from Rangitāhua / Kermadec Islands, Aotearoa / New Zealand, European Journal of Taxonomy 970, pp. 138-174 : 156-160

Metadasynemoides taihua sp. nov.

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Figs 7–10 , Table 2

Diagnosis

Metadasynemoides taihua sp. nov. characterised by body length 1407–1519 µm, presence of relatively few (475–526) body annules, four longitudinal rows of sublateral somatic setae, presence of intracuticular vacuoles in cephalic capsule and body annules, cephalic setae 0.33–0.48 cbd long of similar or slightly greater length than outer labial setae, loop-shaped amphids of similar size in both males and females, presence of precloacal seta, spicules almost straight and gubernaculum without apophyses.

Differential diagnosis

The new species is most similar to M. latus in having a stout, truncated cephalic capsule with a cephalic ratio close to 1, body length less than 2000 µm long, cephalic setae less than 1 cbd long and similar in length to outer labial setae, and a relatively short tail (<6 anal or cloacal body diameters long). Metadasynemoides taihua sp. nov. differs from M. latus in having a longer body length (1407–1519 vs 1015–1169 µm in M. latus ), higher ratio of b (6 vs 4 in M. latus ) and c (9–11 vs 13–14 in M. latus ), different amphid shape (in males: loop-shaped vs multispiral in M. latus ) and wider amphids (6–7 vs 5 µm in M. latus ).

Etymology

‘ Taihua ’ is the seashore. Along with other nematode species, this new species helps maintain and replenish its healthy status. Māori name ‘ toke taihua ’.

Type material

Holotype NEW ZEALAND • ♂; Kermadec Islands , Raoul Island (off Western Spring); 29.22992° S, 177.96448° W; depth 16 m; 22 Nov. 2021; coarse sand and gravel sediments, voyage TMOR2021 , station 85; NIWA 154947 .

Paratypes NEW ZEALAND • 3 ♂♂, 1 ♀; same data as for holotype; NIWA 154948 .

Type habitat and locality

Shallow subtidal, Raoul Island, New Zealand.

Description

Male

Body colourless, cylindrical, tapering slightly towards posterior extremity. Cuticle coarsely annulated along entire body, except for smooth cephalic capsule and terminal cone. One paratype specimen with two small protists attached to cuticle, ca 25 µm in length. Each annule divided into plates by eight longitudinal crests/ ridges extending from cephalic capsule to terminal cone. Epicristae of each annule slightly overlapping adjacent annules; thin membranous layer extending 2–4 µm out from epicristae along entire body length. Cuticle with pairs of lateral lines (grooves) present from slightly posterior to amphids to near level of cloaca. Zygapophyses indistinct. Body annules 2.0–2.4 µm wide (as measured in lateral fields), roughly equal in width throughout pharyngeal and mid-body regions, gradually decreasing in width from cloacal region towards terminal cone, last annule before terminal cone is narrowest (ca 1.5 µm); some body annules fuse together ventrally or dorsally. Intracuticular vacuoles occurring along longitudinal crests of cephalic capsule and cuticle underlying crest /ridges (vanes). Four sublateral longitudinal rows of short somatic setae extending along entire body length, including tail; somatic setae sometimes not visible, giving appearance of cuticle pore being present. One or two sublateral cuticle pores present on one or both sides of amphids; no pore observed on terminal cone. Lateral alae absent, but lateral sides of cuticle smooth (apparently without annulation) in some paratypes from posterior to pharyngeal body region; in all specimens, two faint, lateral longitudinal lines (possibly grooves) extend from below cephalic capsule to at least posterior end of pharyngeal region, not always clearly visible. Cephalic capsule about as long as wide, truncated anteriorly; flexible lip region set off from rigid cephalic capsule by discontinuity in cuticle. Longitudinal crests extending from base of cephalic capsule to base of lip region. Inner labial sensilla not observed. Outer labial setiform, located immediately anterior to cephalic setae 0.33–0.48 cbd long; cephalic setae of similar or slightly greater length than outer labial setae, both located on lip region. Loop-shaped amphids located towards base of cephalic capsule; amphidial aperture of same size and shape as amphidial fovea. Elongated corpus gelatum sometimes visible. Buccal cavity small, funnel shaped, without differentiation, with slightly cuticularized walls. Pharynx cylindrical, subdivided into anterior corpus and posterior postcorpus; corpus ca 60% of pharynx length, uniformly cylindrical, muscular; postcorpus ca 40% of pharynx length, also muscular consisting of short anterior narrower isthmus followed by irregular pharynx outline and slight basal swelling. Pharyngeal glands indistinct. Pharyngeal lumen uniform in thickness, tubes and valve-like structures absent. Cardia 8–14 µm long, surrounded by intestine. Nerve ring surrounding isthmus. Secretory-excretory system present; excretory pore on annule 45–55; ventral gland slightly posterior to cardia.

Reproductive system diorchic with two opposed testes located either both to right or both to left of intestine; anterior testis outstretched, posterior testis reflexed. Spicules paired, symmetrical, weakly arcuate to almost straight along entire length. Gubernaculum plate-like without apophyses. Precloacal seta present, 6–9 µm long. Caudal glands and spinneret present. Terminal cone 21–28 µm long.

Female

Similar to males, but with slightly lower ratio of a and fewer caudal setae. Reproductive system didelphic, amphidelphic, with reflexed ovaries; anterior ovary to the right of intestine and posterior ovary on left of intestine. Anterior ovary with spermatheca. Vulva a transverse slit slightly posterior to mid-body. Vagina straight, with thickened walls, surrounded by sphincter muscle. Pars refringens vaginae not observed. Intrauterine egg not seen. Anal annule similar to adjacent annules.

Figures

Fig. 7. Metadasynemoides taihua sp. nov. A, G. Holotype, ♂ (NIWA 154947). B–F. Paratypes (NIWA 154948). A. Pharyngeal body region. B. ♂, cephalic region. C. ♀, cephalic region. D. ♀, cephalic region. E. ♀, reproductive system. F. ♀, posterior body region. G. Posterior body region. Scale bar: A = 50 µm; B–D = 30 µm; E = 67 µm; F–G = 40 µm.

Fig. 8. Metadasynemoides taihua sp. nov., paratype, ♂ (NIWA 154948), light micrograph. A–E. Anterior body region. F. mid-body cuticle. Scale bar = 20 µm.

Fig. 9.Metadasynemoides taihua sp. nov., holotype, ♂ (NIWA 154947),light micrographs. A. Pharyngeal body region at level of secretory-excretory system (ampulla). B. Mid-body region. Arrows show membrane extending from body annule epicristae. Scale bar = 10 µm.

Fig. 10. Metadasynemoides taihua sp. nov., paratype, ♂ (NIWA 154948), light micrograph. Scale bar = 75 µm.