Halanonchus scintillatulus Leduc, 2020

Leduc, Daniel, Zhao, Zeng Qi & Sinniger, Frederic, 2020, Halanonchus scintillatulus sp. nov. from New Zealand and a review of the suborder Trefusiina (Nematoda: Enoplida), European Journal of Taxonomy 661 (661), pp. 1-45 : 25-32

Halanonchus scintillatulus Leduc sp. nov.

urn:lsid:zoobank.org:act:00164E0B-2084-4DDD-9480-5C5D3D9F1819

Tables 2–3 ; Figs 5–8

Diagnosis

Halanonchus scintillatulus sp. nov. is characterized by body length 1385–1815 μm, papillose inner labial sensilla very close to outer labial setae, cephalic setae 0.20–0.33 cbd long, amphids located posterior to buccal cavity, buccal cavity with discontinuity between gymnostoma and stegostoma walls, slight toothlike projection of anterior edge of stegostoma wall and tail 440–623 μm long. Males with row of 6–12 pharyngeal supplements, 11–21 precloacal supplements and arcuate spicules 1.1–1.3 cbd long; females with vulva at 31–34% of body length from anterior extremity.

Differential diagnosis

Halanonchus scintillatulus Leduc sp. nov. is the smallest species of the genus, with a body length less than 2000 μm ( Table 3 ). The new species is similar to H. arenarius and H. longicaudatus in having papillose inner labial sensilla, but differs from both species in having relatively low values of a (38– 58 vs> 70 in H. arenarius and H. longicaudatus ) and arcuate spicules (vs straight or almost straight spicules in H. arenarius and H. longicaudatus ). Halanonchus scintillatulus sp. nov. also differs from H. arenarius in amphid size (22–33% vs 14% cbd in H. arenarius ), length of cephalic setae and outer labial setae (3–4 μm vs 5–7 μm in H. arenarius ) and number of precloacal supplements (11–21 vs 9 in H. arenarius ); the new species also differs from H. longicaudatus in amphid size (22–33% vs 50% cbd in H. longicaudatus ) and position (posterior to buccal cavity vs at level of anterior half of buccal cavity in H. longicaudatus ). Halanonchus scintillatulus sp. nov. is similar to H. bullatus in the arrangement and size of the cephalic and inner labial setae, amphid size and position, and spicule size and shape, but can be distinguished from the latter by the lower values of a (38–58 vs 87 in H. bullatus ) and b (6–7 vs 10 in H. bullatus ), shorter tail (440–623 μm vs 1270 μm in H. bullatus ; c’ = 21–26 vs 55 in H. bullatus ), fewer pharyngeal supplements (6–12 vs 13–16 in H. bullatus ) and vulva position (%V = 31–34 vs 16 in H. bullatus ).

Etymology

The species name is derived from the latin term ‘ scintillula’, diminutive of ‘ scintillo’ (= sparkle, glitter), and refers to the numerous small, light refractive granules present along the body of most specimens of this species.

Material examined

Holotype

NEW ZEALAND • ♂; North Island , Firth of Thames, Kaharoa voyage KAH0310, site SD5, station 3400C, surface (0–5 cm) muddy sediments; 36.9133º S, 175.4983º E; depth 5 m; 13 Dec. 2003; D. Leduc leg.; NIWA 139240 .

Paratypes

NEW ZEALAND • 2 ♂♂, 2 ♀♀; same collection data as for holotype; NIWA 139241 . • 3 ♂♂, 2 ♀♀; same collection data as for preceding; NNCNZ 3325 to 3329 .

Description

Male

Body cylindrical, slender, colourless except for presence in most specimens of numerous light refractive granules along lateral, ventral and dorsal chords, either along entire body or in pharyngeal and tail regions only. Metanemes not observed. Six minute inner labial papillae very close to the six outer labial setae; the latter each with single joint and narrow tip. Four cephalic setae, apparently without joints, slightly longer than the outer labial setae, 0.20–0.33 cbd long, situated near mid-level of stegostoma, ca 0.6 cbd from anterior extremity. Amphids located posteriorly to buccal cavity. Amphideal aperture oval; amphideal fovea larger, pocket-shaped or sometimes bean-shaped, amphideal duct with slightly cuticularized outline and duct pore visible near middle of amphideal aperture. One or two somatic setae present posterior to each amphid; sometimes one or two dorsal and/or ventral setae present at level of amphid. Somatic setae absent elsewhere. Midventral row of 6–12 pharyngeal supplements present in five out of six specimens, each consisting of a small papilla on a cuticular swelling with internal duct, located 22–69 μm apart, beginning 26–30 μm from anterior extremity to slightly posterior to pharynx. Buccal cavity barrel-shaped, with cuticularized walls, up to 5–6 μm wide and 13–16 μm deep. Discontinuity in cuticularization between gymnostoma and stegostoma walls, and at the junctions between dorsal and ventrosublateral sectors, may be interpreted as outline of “oval structures”; slight projection of stegostoma wall cuticularization into buccal cavity also gives appearance of small tooth-like structure in lateral cross-section. Pharynx cylindrical, muscular, widening slightly posteriorly but without forming true bulb; cardia short, not surrounded by pharyngeal tissue. Nerve ring situated at ca 40–45% of pharyngeal length from anterior end. Secretory-excretory system not observed. Reproductive system with two opposed outstretched testes, both located ventrally relative to intestine. Sperm cells relatively large, 13–17 μm long, 7–9 μm wide, ovoid or drop-shaped, with spindle-shaped nuclei. Spicules arcuate, 1.1–1.3 cbd long, lightly cuticularized; gubernaculum short, ca ¼ of spicule length, flat or slightly curved. Eleven to twenty-one precloacal supplements present along midventral line, similar in structure and size to pharyngeal supplements; posterior-most supplement 12–15 μm from cloaca, remaining supplements 12–35 μm apart with anterior-most supplements tending to be slightly further apart than posterior-most supplements. Precloacal seta not observed. Tail filiform, very long, without setae; three caudal glands present.

Female

Similar to males, but with slightly lower values of a. Reproductive system monodelphic, with single reflexed posterior ovary situated ventrally relative to intestine. Mature eggs 95–103 μm long and 28– 31 μm wide. Spermatheca not observed. Vulva at about one third of body length from anterior extremity. Cuticularized pars distalis vaginae, proximal portion of vagina uterina surrounded by constrictor muscle; vaginal glands not observed.

Figures

Fig. 5. Schematic representation of buccal cavity wall cuticularization in Halanonchus based on observations of Halanonchus scintillatulus Leduc sp. nov. and illustrations of other Halanonchus species. Only the two ventrosublateral sectors are shown (dorsal sector omitted for clarity). Thin lines show contours of gymnostoma, and thick lines show contours of stegostoma.

Fig. 6. Halanonchus scintillatulus Leduc sp. nov. A. ♀, cephalic region, paratype (NNCNZ3329). B. ♂, cephalic region, holotype (NIWA 139240). C. ♂, cephalic region, paratype (NIWA 139241). D. ♂, copulatory apparatus, holotype. E. ♂, posterior body region, holotype. Scale bars: A–C = 20 μm; D = 35 μm; E = 45 μm.

Fig. 7. Halanonchus scintillatulus Leduc sp. nov. A. Entire ♂, holotype (NIWA 139240). B. Entire ♀, paratype (NNCNZ3328). Scale bar = 125 μm.

Fig. 8. Halanonchus scintillatulus Leduc sp. nov., light micrographs, ♀, paratype (NNCNZ3329). A. Sublateral optical cross section of buccal cavity showing teeth-like structures at anterior edge of stegostoma wall. B. Subsurface view of same specimen showing discontinuity in cuticularisation of buccal cavity wall between gymnostoma and stegostoma, and at the junctions between the dorsal and ventrosublateral sectors, which may be interpreted as forming “oval structures”. Abbreviations see Material and methods. Scale bar = 10 μm.