New and known free-living nematode species (Nematoda: Chromadorea) from offshore tsunami monitoring buoys in the Southwest Pacific Ocean

List of valid species

Type locality. Kermadec region (29.6782°S, 175.0127°W), collected during RV Tangaroa voyage TAN2209, from the surface of DART Buoy F, originally deployed in August 2021. Specimens of Atrochromadora tereroa sp. nov. were recovered from filamentous green algae.

Type material. Holotype male (NIWA 181,659); two paratype males and four paratype females (NIWA 181660), collected on 10 August 2022.

Measurements: See Table 2 for detailed measurements.

Description: Males. Body colourless, cylindrical, tapering slightly towards both extremities. Pigment spots (ocelli) not observed. Cuticle with transverse striations and punctations; lateral differentiation consisting of 4–6 longitudinal rows of larger punctations, extending from posterior to buccal cavity to near tail tip. Eight longitudinal rows of short somatic setae, 2–3 µm long, present from posterior to secretory-excretory pore to near tail tip. Cephalic region slightly rounded; lip region not distinctly set off. Inner labial papillae not observed; six short outer labial papillae on lip region, anterior to four cephalic setae, each 0.5–0.6 cbd long. Four sublateral rows of 2–3 cervical setae, each 2–5 µm long. Amphidial fovea cryptospiral, with flattened oval outline, located at level of cephalic setae. Buccal cavity funnel-shaped, with cuticularized walls, 14–15 µm deep and up to six µm wide; one dorsal and two ventrosublateral teeth, solid, strongly cuticularized, equal in size and shape, 4–5 µm long. Pharynx cylindrical, muscular, with oval- to pyriform-shaped posterior bulb; pharyngeal lumen not cuticularised. Nerve ring located at 52–62% of pharynx length from anterior. Secretory-excretory system present; pore located approximately halfway between level of nerve ring and anterior body extremity; pore and distal portion of ampulla cuticularized and surrounded by thin glandular layer; elongated renette cell located posterior to pharynx. Cardia small, short, not surrounded by intestine.

Reproductive system monorchic with single anterior outstretched testis located left relative to intestine. Sperm cells globular, 4–7 × 5–8 µm. Spicules paired, with velum, curved near proximal and distal ends, tapering distally, 1.0–1.1 cloacal body diameters long. Gubernaculum funnel-shaped, strongly dilated distally and denticulated. Ejaculatory glands not observed. Two conspicuous sup-shaped precloacal supplements present, located 25–28 µm anterior to cloaca and 26−28 µm apart. One short precloacal seta present ventrally. Tail conical. Three caudal glands and spinneret present.

Females. Similar to males, but often with slightly longer tail, measuring 4.1–5.1 anal body diameters in length. Reproductive system didelphic, with two opposed and reflexed ovaries; anterior ovary to the right of intestine, posterior ovary to the left. Surface of mature eggs with numerous bumps giving distinctive rough appearance, measuring approximately 25–26 × 45–49 µm. Spermatheca not observed. Vulva situated near mid-body. Proximal portion of vagina surrounded by constrictor muscle, small vaginal glands present. Proximal portion of uterus opposite vulva not conspicuously cuticularized.

Diagnosis. Atrochromadora tereroa sp. nov. is characterised by body length of 728–810 µm, cuticle with lateral differentiation consisting of 4–6 longitudinal rows of larger punctations; cryptospiral amphidial fovea with flattened oval outline; buccal cavity with three equal solid teeth; secretory-excretory pore and distal portion of ampulla with cuticularized outline, surrounded by thin glandular layer; spicules 21–26 µm long (1.0–1.1 cbd); two cup-shaped precloacal supplements in males; and mature eggs with a distinctly rough surface due to the presence of numerous small bumps.

Differential diagnosis. The new species can be distinguished from all other species of the genus in having two precloacal supplements and a buccal cavity with equal-sized teeth. Other congeners possess a buccal cavity with subequal teeth and either no precloacal supplements or at least eight.

Etymology. The species name is a noun in apposition, derived from te reo Māori terms ‘tere’ (meaning to float, drift, swim, flow, glide) and ‘roa’ (meaning a long time) referring to the presumed ability of this species to disperse over long distances.

Key to valid Atrochromadora species:

Subfamily diagnosis (from Tchesunov (2014) and Venekey et al. (2019)) Cuticle usually with complex, heterogenous ornamentation. The six outer labial and four cephalic setiform sensilla may be arranged in a single circle (6+10) or two distinct circles (6+6+4). Amphidial fovea transverse slit-like or oval (elliptical). Buccal cavity with large or small dorsal tooth, with or without denticles or smaller ventrosublateral teeth. Pharynx with or without defined terminal bulb. Gubernaculum usually with hammer- or L-shaped lateral pieces (erroneously referred to as telamon in some descriptions). Precloacal supplements absent in males, but a precloacal differentiation of body cuticle may be present.

Remarks. The subfamily was recently revised by Datta & Al-Helal (2023)

Genus diagnosis (modified from Tchesunov (2014)).

Cuticle complex and heterogeneous, composed of hexagonal or ovoid punctuations in the anterior and posterior regions, with narrower markings confined to the lateral surface along the mid-body. Transversally elliptical amphidial fovea without surrounding cuticle fringe. Six outer labial sensilla and four cephalic sensilla setiform, arranged in separate circles. Buccal cavity with large dorsal tooth, ventrosublateral teeth, and rows of denticles. No distinct pharyngeal bulb. Gubernaculum with prominent hammer or L-shaped lateral pieces.

Remarks. Ten valid Euchromadora species are listed in the review of the family Chromadoridae by Venekey et al. (2019). Euchromadora gaulica Inglis, 1962 may need to be synonymized with E. tokiokai Wieser, 1955 due to overlap in several key body measurements particularly the strong resemblance in the structure of the copulatory apparatus, which is the main diagnostic character differentiating species of the genus.

Type species: Euchromadora vulgaris (Bastian, 1865) de Man, 1886

List of valid species

Type material: Holotype male (NIWA 182672); two paratype males and six paratype females (NIWA 182673), collected on 10 December 2021.

Type locality: New Zealand region, off East Cape (38.2002°S, 179.7690°W), collected during RV Tangaroa voyage TAN2114, from the surface of DART Buoy C, originally deployed in December 2019. Specimens of Euchromadora rebeccae sp. nov. were recovered from filamentous algae and goose barnacles.

Measurements: See Table 3 for detailed measurements.

Description: Males. Body with slight golden colouration, cylindrical, tapering slightly towards both extremities. Pigment spots (ocelli) not observed. Cuticle thickened, particularly in pharyngeal region and near tail tip (4–6 µm), thinner elsewhere (2–4 µm) with ornamentation and annulations visible from slightly posterior to cephalic setae to level of spinneret. Lozenge-shaped or hexagonal structures visible in cephalic and pharyngeal regions, morphing into tightly packed rectangular structures or bars sometimes with lateral differentiation of punctations in the posterior pharyngeal, mid-body and anal regions, reverting to lozenge structures in the tail region. Eight longitudinal rows of somatic setae, 4–5 µm long, extending along entire body length. Cephalic region slightly rounded; lip region not distinctly set off. Six inner labial papillae and six outer labial papillae in separate circles on lip region; four cephalic setae, each 0.3–0.4 cbd long. Cervical setae absent. Amphidial fovea and aperture not observed. Mouth opening surrounded by twelve cuticularized rugae. Buccal cavity funnel-shaped with cuticularized walls, approximately 30 µm deep and up to nine µm wide; one large dorsal tooth (approximately five µm long) and two smaller ventrosublateral teeth, all teeth solid and strongly cuticularised. Two rows of denticles present along the ventrosublateral sectors of the buccal cavity. Pharynx cylindrical, muscular, widening gradually posteriorly but not forming true bulb; pharyngeal lumen not cuticularised. Nerve ring located at 42–49% of pharynx length from anterior end. Secretory-excretory system present, pore located slightly posterior to nerve ring; renette cell approximately 110 × 25 µm, located immediately posterior to pharynx. Cardia medium sized (7–8 µm long), not surrounded by intestine.

Reproductive system monorchic, with single anterior outstretched testis located to the right or left of intestine. Sperm cells globular, 3–4 × 5–6 µm. Spicules paired, curved, widest in middle portion, lacking a velum, tapering distally, measuring 1.8–2.0 cloacal body diameters in length. Gubernaculum with relatively long (51–61 µm), slightly bent dorsal piece, most strongly cuticularized along dorsal side; lateral pieces of the gubernaculum (i.e., telamons) L-shaped, slightly shorter than dorsal piece (38–44 µm), without protrusions or serrations, tapered distally, rounded proximally. One pair of ejaculatory glands present, located 3–4 cloacal body diameters anterior to cloaca. Precloacal supplements absent. One short precloacal seta present ventrally, 4–5 µm long. Tail conical. Three caudal glands present; spinneret well-developed, with terminal pore.

Females. Similar to males, but often with slightly longer tail, measuring 3.9–4.6 anal body diameters in length. Reproductive system didelphic, with two opposed and reflexed ovaries; both ovaries located to the right of intestine. Mature eggs with smooth surface, measuring approximately 38–43 × 49–71 µm. Spermatheca not observed. Vulva situated near mid-body. Proximal portion of vagina without conspicuous constrictor muscle, small vaginal glands not observed. Proximal portion of uterus opposite vulva not conspicuously cuticularised.

Diagnosis: Euchromadora rebeccae sp. nov. is characterised by body length 1,237–2,137 µm, cephalic setae 0.3–0.4 cbd long, equal spicules 1.8–2.0 cloacal body diameters long, L-shaped telamons without protrusions or serrations, 38–44 µm long (0.42–0.45 of spicule length).

Differential diagnosis: The new species is most similar to Euchromadora ezoensis and E. permutabilis in the structure of the copulatory apparatus with equal spicules and simple L-shaped telamons without serration or protrusions. Euchromadora rebeccae sp. nov. differs from both species in having relatively short telamons (44–49 vs ≥ 54 µm in both E. ezoensis and E. permutabilis. The new species also possesses longer spicules relative to E. ezoensis (84–104 µm vs 75–85 µm), and shorter spicules relative to E. permutabilis (84–104 µm vs 104–133 µm). The new species also differs from E. ezoensis in having a shorter body length (1,237–2,137 vs 2,246–3,052 µm in E. ezoensis), smaller maximum body diameter (in males: 47–59 vs 59–74 µm in E. ezoensis; in females: 75–85 vs 94–128 µm in E. ezoensis) and shorter telamon as a proportion of spicule length (0.42–0.45 vs 0.54–0.60 in E. ezoensis), and from E. permutabilis in having a higher ratio of a (in males: 24–27 vs 15–22 in E. permutabilis; in females: 22–24 vs 16–24 in E. permutabilis) and longer tail (in males: c’ = 4.6–4.7 vs 2.5–3.5 in E. permutabilis; in females: c’ = 5.0–5.2 vs 3.0–4.0 in E. permutabilis).

Etymology. The species is named after the author’s partner, Rebecca Joy Styles.

Dichotomous identification key of Euchromadora species

Family diagnosis (from Fonseca & Bezerra (2014)) Small, slender nematodes with body lengths usually less than 2.5 mm. Body cuticle finely striated and often appearing smooth under light microscopy. Anterior sensilla in two crowns: anterior circle with six inner labial sensilla (usually papilliform), posterior circle with six outer labial sensilla and four cephalic (usually setiform) sensilla. Amphidial fovea circular or cryptospiral and ventrally wound, varying in size (possibly due to sexual dimorphism) and in position from the anterior end. Ocelli often present in shallow-water and inland species. Buccal cavity (excluding cheilostome) surrounded by pharyngeal tissue and of varying shape: either bipartite or single V-shaped, cylindrical or minute, with or without denticles. Pharynx cylindrical, well-muscularized, sometimes slightly swollen at its anterior end and in some genera with more or less developed muscular posterior bulb. Cardia composed of a conoid part lying between pharynx and intestine, and oblong valve-like, inner part protruding into intestinal lumen. Intestine with few cells (oligocytous) arranged in two rows; dorsal and ventral. Ventral gland often present in marine and freshwater species; secretory–excretory pore from just anterior to nerve ring to the labial region. Female reproductive system monodelphic-prodelphic, with the gonad almost always outstretched on the right side of intestine. Male monorchic, spicules generally simple, of varying length, one to five times the anal body diameter. Gubernaculum of varying shape: thin without apophysis to robust with apophysis. Spermatozoa spherical. Tail conoid to elongate –conoid, similar in sexes with caudal glands opening through a single pore at the terminal spinneret; terminal setae absent.

Remarks. The family was revised by Fonseca & Decraemer (2008), who provided lists of valid species for all Monhysteridae genera.

Genus diagnosis (modified from Tchesunov, Portnova & Van Campenhout (2015)) Body stout to slender. Cuticle thin and optically smooth. Labial region not set off. Inner labial sensilla papilliform, outer labial and cephalic sensilla setiform. Amphidial fovea circular, relatively small to moderate in size, located less than one to three labial diameters from the cephalic apex. One to three lateral cervical setae present, situated at some distance posterior to the amphidial fovea; other somatic setae sparse, short and inconspicuous. Pharyngostoma cup- to funnel-shaped, small, with cuticularised walls. Pharynx cylindroid, evenly muscular throughout its length. Anteriormost stomach-like portion of the intestine (progaster) composed of four cells, set off from posterior intestine by a constriction. Ventral pore usually at labial region if discernible; ventral gland cell body large and situated at anterior intestine. Female ovary long, outstretched and located to the right of the intestine; vulva often but not always located close to the anus; posterior cuticular wall of the vagina may be thickened and cuticularised (pars refringens vaginae) closer to the vulva. Uterus of ripe females normally filled with numerous eggs and embryos; possibly most species ovoviviparous. Male gonad long, outstretched and located to the right of the intestine. Spicules slender and arcuate, slightly knobbed posteriorly. Gubernaculum with a short dorso-caudal apophysis. One midventral preanal papilla close to the cloacal opening and two or three pair of subventral papillae on the posterior half of the tail present. Three caudal glands present, two of them very conspicuous; terminal conical spinneret with an internal funnel-like structure.

Type species: Halomonhystera disjuncta (Bastian, 1865) Andrássy, 2006

Remarks. The genus was most recently revised by Tchesunov, Portnova & Van Campenhout (2015). The latter authors retained H. paradisjuncta (De Coninck, 1943) Tchesunov, Portnova & Campenhout, 2015 as a valid species even though it had been synonymised with H. disjuncta by Andrássy (2006). No justification was provided for this decision, however the species is provisionally retained here pending a more thorough revision of the genus.. The diagnosis by Tchesunov, Portnova & Van Campenhout (2015) states that the ventral pore is located at the labial region (when discernible). However, in some species such as H. cameroni (Steiner, 1958) Andrássy, 2006 and H. tangaroa Leduc, 2014, the ventral pore is located well posterior to the buccal cavity.

Tchesunov, Portnova & Van Campenhout (2015) also noted that certain species of the closely-related genus Thalassomonhystera possess all the diagnostic characters of Halomonhystera except for the position of the vulva, which may be located more anteriorly relative to the anus. They stated that the position of the vulva can be in conflict with a number of other Halomonhystera characters. They concluded that the vulva can vary gradually in position from one species to another and does not necessarily need to be located far posteriorly (as stated in in previous diagnoses of the genus Halomonhystera) for a species to be ascribed to Halomonhystera, as long as the other characters agree with the genus diagnosis. The overlap between the genera Halomonhystera and Thalassomonhystera includes not only the position of the vulva, but also other morphological characters such as tail shape (conical in all Halomonhystera species and in some Thalassomonhystera species), buccal morphology (either simple or double in Halomonhystera and simple in all Thalassomohystera species), and amphid size (small to medium in Halomonhystera and small to large in Thalassomonhystera).

The only trait which appears to differ consistently between Halomonhystera and Thalassomonhystera as they are currently defined by Tchesunov, Portnova & Van Campenhout (2015) and Fonseca & Decraemer (2008), respectively, is the presence of precloacal and caudal papillae in Halomonhystera and their absence in Thalassomonhystera. This difference was not discussed by Tchesunov, Portnova & Van Campenhout (2015), however, given the overlap in other key morphological characteristics previously used to distinguish between the two genera (i.e., the position of the vulva and buccal morphology in particular), it appears that the presence or absence of pre- and postcloacal papillae constitutes the best available character to differentiate Halomonhystera from Thalassomonhystera. According to this new definition, Thalassomonhystera refringens (Bresslau & Schuurmans Stekhoven, 1933) Jacobs, 1987 and T. anoxybiotica (Jensen, 1986) Jacobs, 1987 need to be transferred to Halomonhystera as they both possess precloacal and caudal papillae.

Halomonhystera zhangi (Li, Huang & Huang, 2024) was recently described from coastal Sargassum in the Yellow Sea, and is morphologically identical to H. refringens (Bresslau & Schuurmans Stekhoven, 1933) comb. nov. in most key characteristics, including body length, body ratios (a, b, c and c’), size and arrangements of anterior sensilla, position of vulva (relatively far anteriorly for the genus), amphid size and position, stoma shape, and presence and position of pre- and postcloacal papillae (Li, Huang & Huang, 2024). The only slight inconsistencies are slightly longer spicules in H. zhangi (41–45 vs 39–40 µm in H. refringens) and opening of secretory-excretory system just posterior to level of cephalic setae (vs further posteriorly in H. refringens). The latter may be an erroneous observation; this feature can be difficult to observe and photomicrographs of the holotype specimen appear to show the secretory pore at same level as the ampulla, as indicated by a slight bulge on cuticle (Fig. 2A in Li, Huang & Huang, 2024). On balance, I suggest that H. zhangi be synonymised with H. refringens.

A tabular key to Halomonhystera species updated from Tchesunov, Portnova & Van Campenhout (2015) is provided in Tables S1 and S2.

List of valid Halomonhystera species:

Material examined: Three males and three females (NIWA 182674), collected on 10 December 2021.

Sampling location. New Zealand region, off East Cape (38.2002°S, 179.7690°W), RV Tangaroa voyage TAN2114, collected from surface of DART Buoy C, originally deployed in December 2019. Specimens were recovered from filamentous algae and goose barnacles.

Distribution: Cosmopolitan. North Sea (Schuurmans Stekhoven Jr 1935; Warwick, Platt & Somerfield, 1998), Chile (Wieser, 1956), Washington coast (USA; Wieser, 1959), Japan (Kito, 1981), Yellow Sea (Li, Huang & Huang, 2024), New Zealand (present study).

Description: Males. Body colourless, cylindrical, tapering slightly towards both extremities. Cuticle smooth with faint striations visible in some specimens. Sparse sublateral somatic setae, 4–5 µm long, sometimes in pairs. Cephalic region slightly rounded, not set-off. Inner labial papillae not observed; six outer labial setae and four cephalic setae of similar length and in single circle, ca. 0.3 cbd long, located on lip region usually near base. Ocelli not observed. Amphidial fovea circular with lightly cuticularized outline, medium-sized, situated ca. 0.5 cbd from anterior end. Buccal cavity funnel-shaped, with lightly cuticularized walls, 5–7 µm deep, up to four µm wide. Pharynx cylindrical, muscular, without posterior bulb; pharyngeal ducts sometimes visible. Pharyngeal lumen not cuticularised. Nerve ring at ca. 65% of pharynx length from anterior. Secretory-excretory system present; pore located at 16–18% of pharyngeal length from anterior, ampulla small, renette cell large, 10–17 × 30–32 µm, located posterior to pharynx. Cardia small, four µm long, partially surrounded by intestine; intestine of one specimen with multiple diatom frustules, 3 × 14–18 µm.

Reproductive system monorchic, with single anterior outstretched testis (though folds usually present), located to right of intestine. Sperm cells globular, ca. 2 × 2–3 µm. Spicules paired, curved, with thin velum, tapering distally, 2.0 cloacal body diameters long. Gubernaculum with straight dorsal piece, without apophyses, surrounding spicules distally, ca. 15 µm long. Precloacal papilla present ventrally, 32–40 µm anterior to cloaca; another ventral papilla usually present immediately anterior to cloaca. Postcloacal papillae located 7–9, 37–42 and 57–60 µm posterior to cloaca. Anteriormost postcloacal papilla consist of pair of subventral papillae, not always distinct, each bearing one short (two µm) seta; second ventral postcloacal papillae most conspicuous, bearing pair of short (two µm) setae; posteriormost ventral postcloacal papilla bearing two pairs of short (two µm) setae. Tail conical, with short terminal cyclindrical portion and few short (3–5 µm) and sparse subdorsal setae. Three caudal glands and spinneret present.

Females. Similar to males, but with slightly smaller amphids and slightly longer tail. Reproductive system monodelphic with single anterior outstretched ovary (though fold usually present), located to the right of intestine; mature eggs ca. 20 × 40 µm. Spermatheca not observed. Vulva situated slightly posterior to mid-body. Proximal portion of vagina surrounded by constrictor muscle; vaginal glands present.

Remarks. The Halomonhystera refringens (Bresslau & Schuurmans Stekhoven, 1933) comb. nov. specimens from DART Buoy C off New Zealand’s East Cape, agree well with the original description of the species based on material from the North Sea (Schuurmans Stekhoven Jr 1935). The main difference is the longer spicules in the New Zealand specimens (2.0 cloacal body diameters) compared to those from the North Sea (1.45 cloacal body diameters; Schuurmans Stekhoven Jr 1935, Bresslau & Schuurmans Stekhoven Jr, 1940) and also Chile (1.25 cloacal body diameter; Wieser, 1956). In contrast, descriptions based on specimens from Puget Sound (Pacific coast, USA) and Japan report spicule lengths similar to the New Zealand specimens (35–41 µm, or approximately 2.0 cloacal body diameters, as inferred from published illustrations).

Previous descriptions of H. refringens consistently note the presence of a precloacal papilla, along with the two posteriormost ventral postcloacal papillae. The pair of subventral postcloacal papillae, each bearing a single short seta, as described here for the New Zealand material, has not been explicitly mentioned in earlier accounts. However, these structures are not always clearly visible depending on the orientation of the specimen, and all previous descriptions do refer to the presence of setae associated with these papillae.