Halichoanolaimus ovalis Ditlevsen, 1921

Leduc, Daniel, 2020, New and known Halichoanolaimus de Man, 1886 species (Nematoda: Selachinematidae) from New Zealand’s continental margin, European Journal of Taxonomy 726, pp. 59-82 : 61-66

Halichoanolaimus ovalis Ditlevsen, 1921

Table 1 , Figs 1–3

Material examined

NEW ZEALAND • 2 ♂♂, 1 ♀; Kaikōura Canyon , 42.5082° S, 173.6325° E; water depth 1061 m; voyage TAN1006 station 7, site K4; 3 May 2010; NIWA 139245 .

Type locality

North Arm of Carnley Harbour, Auckland Islands .

Description

Males

BODY. Cylindrical, tapering slightly towards anterior extremity. Cuticle with transverse rows of punctations; lateral differentiation consisting of larger, more widely spaced punctations. Two dorsosublateral rows of

pore complexes extending from posterior to nerve ring to cloacal region, each pore complex ca 1.5 µm in diameter, becoming more closely spaced posteriorly. Up to two or three ventrosublateral pore complexes also present in pharyngeal region or slightly posterior to pharynx. Eight longitudinal rows of short, sparse somatic setae, 2–3 µm long. Cephalic region slightly rounded, with slight indentation immediately posterior to cephalic setae. Lip region not conspicuously differentiated, bearing six inner labial papillae. Six short outer labial papillae, 2 µm long, located at base of labial region and at same level as four cephalic papillae of same length. Amphideal fovea multispiral with 5.0 to 5.25 turns, situated ~0.4 cbd from anterior end. Buccal cavity (pharyngostome) large, 25–30 µm deep, divided into anterior (gymnostome) and posterior portions (stegostome). Anterior portion of buccal cavity cup-shaped, with three sets of six cuticularized rhabdions, 12–14 µm long, terminating in three sets of at least six pairs (one anterior and one posterior) of denticles; posterior portion of buccal cavity narrower, cylindrical, surrounded by three Y-shaped pairs of cuticularized rhabdions with swollen bases, 15–17 µm long. Pharynx cylindrical, muscular, without anterior or posterior bulb. Nerve ring at ca 45–50% of pharynx length from anterior. Secretory-excretory system present; renette cell up to 18 µm wide and 18 µm long, situated at level of cardia. Several nucleated pseudocoelomocytes also present around base of pharynx and either side of secretory-excretory duct; ampulla slightly smaller than renette cell, pore situated posterior to nerve ring. Cardia small, surrounded by intestine; posterior extremity of intestine blind.

REPRODUCTIVE SYSTEM. Diorchic with outstretched testes. Anterior testis to the right or ventrally to intestine, posterior testis to the left side of intestine. Sperm cells globular, 8–12 × 15–17 µm. Spicules paired, curved, tapering distally, length 1.5–1.6 body diameters at level of cloacal opening; minute ventral denticle present at one third of spicule length from distal tip, interior of spicules granular in appearance. Gubernaculum consisting of two detached lateral pieces (crurae) tapering distally, median portion of gubernaculum (corpus and cuneus) not visible. Seven precloacal supplements present, consisting of conical papillae set on cylindrical cuticular elevations each with internal duct, supplements located 10– 14 µm from each other. Tail conicocylindrical with cylindrical portion ca two thirds of total tail length; a few short and sparse somatic setae present subventrally and subdorsally. Three caudal glands located posterior to spicules, spinneret present.

Females

Similar to males but with slightly longer tail. Reproductive system didelphic-amphidelphic, with reflexed ovaries. Anterior ovary to the left of intestine and posterior ovary to the right of intestine. Vulva situated at mid-body. Mature eggs not observed. Proximal portion of vagina surrounded by constrictor muscle, two large and conspicuous vaginal glands with coarsely granulated cytoplasm and large nucleus present. Intestine blind, no rectum or anus.

Remarks

Halichoanolaimus ovalis was originally described by Ditlevsen (1921) based on two females from the Auckland Islands, and males were later described from the littoral zone of Campbell Island by Allgén (1927) (both Auckland and Campbell islands are located in the Southern Ocean directly south of New Zealand’s South Island). The female specimen from Kaikōura Canyon broadly resembles the original description of Ditlevsen (1921), although the Kaikōura Canyon female is shorter (body length 1.4 vs 1.8 mm in H. ovalis ) and has a higher ratio of ‘a’ (24 vs 18). Ditlevsen (1921) states that the amphideal fovea of H. ovalis females has six turns; however, his figure shows only five turns, which is consistent with the Kaikōura Canyon specimen. The present description is also consistent with the observation of conspicuous vaginal glands with coarsely granulated cytoplasm by Ditlevsen (1921). The two male specimens from Kaikōura Canyon agree well with the description of Allgén (1927) in general body dimensions, although like the Auckland Islands specimens, the Campbell Island specimens are somewhat stouter as indicated by a lower value of ‘a’ (17) relative to the Kaikōura Canyon specimens (22). In addition, Allgén counted only four amphideal fovea turns in his male specimens compared to five in the Kaikōura Canyon specimens. However, the structure of the copulatory apparatus, as well as the shape and number of precloacal supplements, are the same.

The intestine of one of the male H. ovalis specimens contained the anterior half of a nematode prey which was identified as belonging to Halalaimus de Man, 1888 based on the structure of the cuticle, amphideal fovea and buccal cavity. The intestine of the other H. ovalis male (from the same sample) contained the posterior half of a nematode, possibly also belonging to the genus Halalaimus .

Figures

Fig. 1. Halichoanolaimus ovalis Ditlevsen, 1921 A. Male anterior body region. B. Posterior male pharyngeal region and anterior intestinal region showing location of pseudocoelomocytes. C. Female cephalic region. D. Male cephalic region. E. Male posterior body region. F. Female posterior body region. Scale bar: A = 50 µm; B = 37 µm; C, E = 27 µm; D = 25 µm; F = 35 µm.

Fig. 2. Halichoanolaimus ovalis Ditlevsen, 1921 A. Entire Ƌ. B. Entire ♀. Scale bar: 200 µm.

Fig. 3. Halichoanolaimus ovalis Ditlevsen, 1921. Light micrographs. A. Female cuticle showing lateral differentiation and pore complexes (arrow). B. Vulva, showing vaginal glands. C. Copulatory apparatus. Scale bar: A, C = 5 µm; B = 15 µm.

Tables

Table 1. Morphometrics (µm) of three new and one known species of Halichoanolaimus de Man, 1886 from New Zealand’s continental margin. Abbrevations = a, body length/maximum body diameter; b, body length/pharynx length; c, body length/tail length; cʹ, tail length/body diameter at level of cloacal opening or anus; cbd, corresponding body diameter; F, length of cylindrical portion of tail as % of total tail length; L, total body length; V, vulva distance from anterior end of body; %V, V/total body length × 100.*Because females lack an anus, tail length in females was measured from posterior edge of blind intestine, and the commonly used morphometric “anal body diameter” was measured at posterior edge of the blind intestine.

Species	Halichoanolaimus ovalis Ditlevsen, 1921			Halichoanolaimus ossilagulus sp. nov.				Halichoanolaimus funestus sp. nov.			Halichoanolaimus pumilus sp. nov.
	Males		Female	Males		Females		Male	Females		Male
Specimen	M1	M2	F1	Holotype M1	Paratype M2	Paratype F1	Paratype F2	Holotype M1	Paratype F1	Paratype F2	Holotype
L	1461	1453	1356	1068	966	1192	1267	2709	3006	2786	756
a	22222422171817232020	22222422171817232020	22222422171817232020	22222422171817232020	22222422171817232020	22222422171817232020	22222422171817232020	22222422171817232020	22222422171817232020	22222422171817232020	15
b	775	775	775	7	6	7	8	7	99	99	7
c*	89711	89711	89711	89711	913	913	9	8109	8109	8109	6
cʹ *	4.1	3.7	5.0	2.9	3.0	2.4	3.2	6.3	5.7	5.1	4.7
Head diam. at ceph. setae	29	29	30	20	23	24	23	40	46	44	20
Length of outer labial sensilla	2	2	2	1–2	1–2	1–2	1–2	3–4	4	3	3–4
Length of cephalic sensilla	2	2	2	1–2	1–2	1–2	1–2	3–4	4	3	3–4
Amphid height	12	12	12	8	8	8	9	15	12	13	10
Amphid width	15	16	16	12	11	11	11	17	17	17	15
Amphid width/cbd (%)	38	38	40	43	37	33	33	29	27	30	58
Amphid from anterior end	15	15	16	6	7	8	11	26	24	23	8
Nerve ring from anterior end	103	87	114	83	89	99	92	156	145	154	65
Nerve ring cbd	54	61	50	44	51	54	56	94	117	113	40
Excretory pore from anterior end	117	105	147	95	96	111	101	212	183	184	84
Pharynx length	211	209	256	150	151	162	160	377	348	317	115
Pharyngeal diam. at base	43	46	38	33	39	42	56	81	90	93	30
Pharynx cbd	61	64	53	47	53	56	64	110	125	121	42
Max. body diam.	65	66	56	48	58	68	75	120	148	141	49
Spicule length	68	73	–	56	59	–	–	97	–	–	49
Gubernacular apophyses length	37	43	–	26	24	–	–	47	–	–	24
Cloacal/anal body diam.*	45	46	40	33	36	38	46	54	55	62	29
Tail length*	183	170	200	95	109	91	147	341	311	317	136
F	68656654574872778077	68656654574872778077	68656654574872778077	68656654574872778077	68656654574872778077	68656654574872778077	68656654574872778077	68656654574872778077	68656654574872778077	68656654574872778077	61
V	–	–	639	–	–	625	574	–	1341	1288	–
%V	––	––	47	–	–	5245	5245	–	4546	4546	–
Vulval body diam.	–	–	56	–	–	68	75	–	130	137	–