Two new nematode species (Plectida: Leptolaimidae, Rhadinematidae) from Chatham Rise, New Zealand

Two new species of the order Plectida are described from Chatham Rise, New Zealand. Leptolaimus dififtinus sp. nov. is characterised by the short body 319–420 microns long, truncate labial region slightly offset from body contour and bearing conspicuous outer labial papillae, cephalic setae 1.3–1.4 microns long, amphid located 4–9 microns from anterior end, lateral alae originating from middle of buccal cavity length, female without supplements, male with precloacal and postcloacal pairs of subventral setae, nine tubular supplements (alveolar supplements absent), tubular supplements weakly S-shaped with pointed tip, spicules arcuate 24 microns or 1.4 cloacal body diameters long and dorsal gubernacular apophyses. Lavareda iramscotti sp. nov. is characterised by adult body length 3,023–3,121 microns long, eight longitudinal rows of body pores each with short papilla, cephalic setae 4–5 microns long, tail 146–165 microns long, male with spicules 54 microns long, gubernaculum with triangular apophyses, 20 precloacal supplements with bifid distal tips arranged in 9 + 1 + 10 pattern, female with vulva at 55% of body length from anterior and cuticularisation perpendicular to vagina at level of vulva. The present study provides the first record of a Leptolaimus species from the New Zealand region and the first description of a female specimen of the genus Lavareda.


MATERIALS & METHODS
Samples were obtained from Chatham Rise, a submarine ridge that extends eastwards from the South Island of New Zealand, over water depths ranging from ca. 250 to 3,000 m. Samples were collected from Chatham Rise during NIWA cruise TAN0705 (March-April 2007) and TAN1103 (February 2011) under Special Permit 666 granted to NIWA by the Ministry for Primary Industries. Sediment samples were collected and processed as described in Leduc (2012), using an Ocean Instruments MC-800A multicorer (core internal diameter = 9.5 cm). Each sample consisted of one subcore of internal diameter 26 mm taken to a depth of 5 cm. Samples were fixed in 10% formalin and stained with Rose Bengal. Samples were subsequently rinsed on a 45 µm sieve to retain nematodes. Nematodes were extracted from the remaining sediments by Ludox flotation and transferred to pure glycerol (Somerfield & Warwick, 1996).
Species descriptions were made as described in Leduc (2020), based on glycerol mounts using differential interference contrast microscopy and drawings were made with the aid of a camera lucida. Measurements were obtained using an Olympus BX53 compound microscope with cellSens Standard software. All measurements are in µm, and all curved structures are measured along the arc. The terminology used for describing the arrangement of morphological features such as setae follows Coomans (1979). Type specimens are held in the NIWA Invertebrate Collection (Wellington).
The electronic version of this article in Portable Document Format (PDF) will represent a published work according to the International Commission on Zoological Nomenclature (ICZN), and hence the new names contained in the electronic version are effectively published under that Code from the electronic edition alone. This published work and the nomenclatural acts it contains have been registered in ZooBank, the online registration system for the ICZN. The ZooBank LSIDs (Life Science Identifiers) can be resolved and the associated information viewed through any standard web browser by appending the LSID to the prefix http://zoobank.org/. The LSID for this publication is: urn:lsid:zoobank.org:pub:4689626F-D42C-464A-BB0B-55D593DD3E71. The online version of this work is archived and available from the following digital repositories: PeerJ, PubMed Central and CLOCKSS. Gadea, 1973Family Leptolaimidae Örley, 1880Genus Leptolaimus De Man, 1876=Halaphanolaimus Southern, 1914=Aplectus Cobb, 1914=Dermatolaimus Steiner, 1916=Polyaimium Cobb, 1920=Alveolaimus Alekseev & Rassadnikova, 1977=Boveelaimus Alekseev, 1979=Tubulaimus Alekseev & Rassadnikova, 1977 Generic diagnosis: (from Holovachov (2014)) Lateral alae present. First annule anterior to cephalic setae bases and amphids, cephalic capsule absent. Cephalic sensilla papilliform or setiform. Amphideal aperture ventrally unispiral, without central elevation. Secretoryexcretory system present; excretory canal short, excretory ampulla present. Ovary branches reflexed antidromously. Alveolar or tubular supplements present in females of some species, either in pharyngeal or pre-anal regions, or in both positions. Male reproductive system diorchic. Number of supplements varies from zero to 40 for alveolar and zero to 11 for tubular; males may have both types of supplements, one or no supplements at all. Caudal glands and spinneret present or absent.

Order Plectida
Type species: L. papilliger De Man, 1876 Remarks. The genus was revised by Holovachov & Boström (2013) who provided a key to the identification of all 58 valid species based on features of both males and females. Two species were subsequently described by Tchesunov (2015) and Qiao, Jia & Huang (2020 Measurements: See Table 1 for detailed measurements. Description: Male. Body colourless except for dense brown granules in anterior portion of intestine, fusiform, strongly curved ventrally (maybe as a result of formalin fixation), strongly tapering anteriorly in pharyngeal region and posteriorly on tail. Cuticle annulated, annules ca. 1.3 µm apart; lateral alae present consisting of raised, non-annulated cuticle ca.
2.5-3.0 µm wide extending from middle of buccal cavity length (close to first body pore) to almost half of tail length. Four longitudinal rows of sublateral body pores, extending from middle of buccal cavity to two thirds of tail length, pores in pharyngeal region with short papilla, pores posterior to pharynx without papillae; epidermal glands not observed. Somatic setae absent except for a pair of subventral setae, 2 µm long, anterior to cloaca, and second pair of subventral setae posterior to cloaca. Labial region truncate, slightly offset from body contour, lips fused. Inner labial sensilla indistinct; outer labial sensilla conspicuous and papillose, located on the outer surface of lips. Cephalic sensilla setiform, 0.25-0.30 cbd long. Ocelli absent. Amphideal fovea round, located at level of anterior quarter of buccal cavity. Buccal cavity uniformly tubular: cheilostom and gymnostom short, undifferentiated; stegostom tubular, with uniformly thickened lumen. Pharynx muscular, cylindrical anteriorly, with distinct oval basal bulb, distinctly cuticularized lumen from posterior to buccal cavity to near posterior end of pharynx; valvular apparatus absent. Pharyngeal glands and their orifices indistinct. Nerve ring surrounding pharynx near middle of pharynx length. Secretory-excretory system not observed. Cardia cylindrical, with posterior part embedded in intestine.
Reproductive system diorchic with both testes directed anteriorly; one larger outstretched testis located to the right of intestine with globular sperm ca. 2 µm in diameter, one smaller outstretched (possibly reflexed) testis located ventrally with smaller globular sperm ca. 1 µm in diameter. Spicules paired, symmetrical, arcuate, 1.4 cloacal body diameter long, only slightly cuticularised; capitulum rounded, shaft and blade gradually tapering distally. Gubernaculum with lightly cuticularized, bent dorsal apophysis. Ventral precloacal seta not observed. Accessory apparatus composed of nine more or less evenly spaced midventral tubular supplements (posterior supplements appear closer together due to body curvature), ca. 16-23 µm apart, extending for 8 µm from cloaca towards anterior end; alveolar supplements absent. Tubular supplements weakly S-shaped, with pointed tip, 11-14 µm long, each with small drop-shaped subsurface cuticularisation immediately anterior. Tail conical; three caudal glands and spinneret present.
Female. Similar to male, but without any somatic setae, lower values of 'a' and shorter tail. Reproductive system with single anterior reflexed ovary located ventrally; posterior ovary likely present but obscured by large egg in uterus. Spermathecae not observed. Vulva situated slightly posterior to mid-body. Vagina slightly anteriorly directed, short, proximal portion encircled by single sphincter muscle. Vaginal glands not observed. Supplements absent.

Notes.
a, body length/maximum body diameter; b, body length/pharynx length; c, body length/tail length; c , tail length/anal or cloacal body diameter; cbd, corresponding body diameter; L, total body length; n, number of specimens; V, vulva distance from anterior end of body; %V, V/total body length × 100.
versus 4.7-7.1 cloacal/anal body diameters long in L. septimus), shorter spicules (24 versus 31-34 µm in L. septimus) and number and shape of precloacal supplements (9 supplements with pointed tips versus 4-5 supplements with bifid tips in L. septimus). Etymology: The species name is an arbitrary combination of letters (ICNZ Article 11.3) and refers to the sampling site (D15) where the type specimens were collected.
Measurements: See Table 1 for detailed measurements. Description: Male. Body colourless in glycerin preparations, long, slender, uniform in diameter throughout most of body, tapering towards both ends. Cuticle annulated from posterior to cephalic setae to spinneret, annules ca. 1.2 µm apart, without ornamentation or lateral differentiation. Eight longitudinal rows of body pores (two subdorsal, two subventral and four sublateral) extending from posterior to buccal cavity to tail region; each pore with a short conical papilla and connected to small, barely visible epidermal gland. Cephalic region slightly rounded, with reduced labial region. Inner labial sensilla indistinct, outer labial sensilla papilliform, four cephalic setae 0.4-0.5 cbd long. Amphideal fovea ca. 1 cbd from anterior extremity, ventrally unispiral; corpus gelatum not observed. Buccal cavity narrow, deep, tubular, without teeth; cheilostom distinct, resembling a crown, 5 µm in diameter, consisting of a cuticularized ring with six small anteriorly-directed projections (one dorsal, one ventral and four lateral in position). Pharynx muscular, gradually widening posteriorly from posterior to buccal cavity and ending in an oval posterior bulb; pharyngeal lumen cuticularized from posterior to buccal cavity and most thickly cuticularized within posterior pharyngeal bulb. Nerve ring located slightly posterior to middle of pharynx length. Cardia small, 8 µm long, embedded within intestine. Secretory-excretory system with slightly cuticularized pore located posterior to nerve ring and small ampulla; four pairs of medium to large glands with clear cytoplasm located on each side of intestine, up to 33 × 16 µm, starting from ca. 1-2 cbd posterior to pharynx, followed by two pairs of glands with more opaque cytoplasm immediately posteriorly, each gland with duct extending anteriorly.
Female. Similar to male, but with lower 'a' ratio and smaller amphid. Reproductive system with two opposed, reflexed ovaries; anterior ovary situated to the right of intestine and posterior ovary situated to the left of intestine. Spermathecae not observed. Vulva situated slightly posterior to mid-body. Vagina straight, with thick cuticle, two vaginal glands present. Thin cuticularisation centred at level of vulva and perpendicular to vagina, ca. 1 vulval body diameter long. Sphincter muscle not observed. Supplements absent.
Juveniles. Similar to female but body slightly shorter and ' c ' ratio slightly lower. Genital primordium present.
Differential diagnosis: The new species differs from the two other Lavareda species, L. coronatus (Ditlevsen, 1930) Da Fonsêca-Genevois, Smol &Bezerra, 2011 andL. decraemerae, by the presence of longitudinal rows of body pores (versus pores absent in L. coronatus and L. decreamerae). Additional differences between the male of L. iramscotti sp. nov. and L. decraemerae are: greater body length (3.0 versus 2.5 mm in L. decraemerae), shorter cephalic setae (4-5 versus 9 µm in L. decraemerae), absence of cervical setae (versus eight cervical setae in L. decraemerae), longer spicules (54 versus 30 µm in L. decraemerae), and number and arrangement of precloacal supplements (20 supplements in 9 + 1 + 10 arrangement versus 19 supplements in continuous row in L. decraemerae). Furthermore, the secretory-excretory system in L. decraemerae comprises five glands, two of which are located on the right of the intestine and three on the left side of the intestine; Lavareda iramscotti sp. nov. is characterised by an secretory-excretory system with ten glands, five located on either side of the intestine. Lavareda iramscotti sp. nov. can be differentiated from L. coronatus by the higher 'a' ratio (104 versus 63 in L. coronatus), higher 'b' ratio (17 versus 14 in L. coronatus), lower 'c' ratio (18 versus 24 in L. coronatus), presence of cephalic setae (versus absent in L. coronatus), longer tail (165 versus 114 µm in L. coronatus), male reproductive system with two testes (versus one testis in L. coronatus), presence of precloacal seta (versus absent in L. coronatus), and arrangement of precloacal supplements (9 + 1 + 10 versus 9 + 11 arrangement in L. coronatus). Etymology: The species name is an arbitrary combination of letters (ICNZ Article 11.3) which acknowledges my colleague Scott Nodder, who owing to his persistence and bloody-mindedness (the latin ira translates to wrath, anger, fury), managed to obtain the large number of sediment cores required for my postdoctoral research.

DISCUSSION
The present study provides the first record and description of a Lavareda female. Lavareda iramscotti sp. nov. females are characterized by two reflexed genital branches, as in the closely-related genus Rhadinema Cobb, 1920 and like the majority of other plectid taxa. The new species does not exhibit pronounced sexual dimorphism in features such as the buccal cavity, amphids, or tail. The diagnosis of the genus was modified to take into account the presence of body pores and epidermal glands in both sexes of the new species.
Lavareda coronatus was described from ca. 64 m water depth in the Colville Channel (Hauraki Gulf), North Island of New Zealand. Lavareda iramscotti sp. nov., also described from a New Zealand locality though from greater depth and further south, shows some close similarities with L. coronatus in the structure and size of the amphids and spicular apparatus, and both species have the same number of precloacal supplements. Some of the features of L. coronatus which differ from the new species, i.e., the apparent absence of body pores, cephalic setae, and precloacal seta in L. coronatus, may conceivably be the result of poor specimen condition (e.g., broken cephalic setae) or may have been missed in the original description. However, given the additional differences between Ditlevsen's and my male specimens, notably in the 'a', 'b', and 'c' ratios, arrangement of the precloacal supplements, and number of testes, I consider it most likely that the two species are indeed different, even though they belong to a rare genus and were both described from New Zealand localities.

CONCLUSIONS
The present study provides the first record of a Leptolaimus species from the New Zealand region and the first description of a female specimen of the genus Lavareda. At least a dozen additional, yet to be described Leptolaimus species inhabit continental slope environments of New Zealand (D Leduc, 2012, unpublished data). Further research is needed to better characterise the diversity of this genus as well as that of other plectid nematodes across the region's seabed habitats.

Abbreviations a
body length/maximum body diameter b body length/pharynx length c body length/tail length c tail length/anal or cloacal body diameter cbd corresponding body diameter L total body length n number of specimens V vulva distance from anterior end of body %V V/total body length × 100