Synoecnema watinagii, Ivanova, Elena S., Sumaya, Nanette Hope N. & Spiridonov, Sergei E., 2015

Ivanova, Elena S., Sumaya, Nanette Hope N. & Spiridonov, Sergei E., 2015, Synoecnema watinagii (Drilonematoidea: Ungellidae: Synoecneminae), a new nematode species parasitic in earthworms from the Philippines with the first molecular and SEM data for the genus, Zootaxa 3957 (1), pp. 120-130 : 121-126

Synoecnema watinagii sp. n.

( Figs 1 & 2 )

Measurements. Table 1 .

Adult: Small but corpulent nematodes lacking sexual dimorphism in body shape and the morphology of anterior end. Body tapered towards anterior extremity, posterior body portion massive, almost uniformly broad, tail tip broadly conical, short ( Fig. 1 A & B) or forming exceedingly short spike ( Fig. 2 A). Cuticle thin, transversely striated. Epidermis thick. Lateral fields absent. Anterior usually curved, may be ventrally or dorsally. Cephalic hooks sub-terminal, paired, small, curved, thickened, and directed dorsad. Hook bases 5–6 µm long, blades 4–5 µm long, closely positioned with distal tips moderately diverging and directed toward hook base at acute angle. Hook blade positions relatively fixed, with apparently limited ability to move toward or away from sagittal plane. Cephalic sensilla and amphids indiscernible. Mouth and stoma indistinct. Pharynx clavate, always with strongly curved muscular corpus and basal muscular-glandular, rounded bulb which is displaced dorsally in the body. Corpus cylindrical, ca. 3–4 times longer than bulb, isthmus absent. Nerve ring quite thick, surrounding posterior of corpus. Excretory pore on slight protuberance at the level of nerve ring. Excretory duct moderately cuticularized, collapsed or inflated up to 3 µm diameter. Excretory gland large. Intestine thick-walled, forming a prominent bubble-like structure (cardia?) at junction with basal bulb. Posterior course of intestine difficult to see. Caudal organs long deep slits surrounded by striated band situated mid-laterally on the surface of posterior half of body; slits lacking cuticle. Modified, amorphous mass present inside tail region. No duct inside caudal organ observed.

Female: Body tapering towards head end from level of vulva. Pharynx with corpus 58–80 (65±9) µm long and 8–10 (9±1) µm wide, and basal bulb 17–27 (22±5) µm long and 15–20 (18±2) µm wide. Anus absent. Tip of ovary extending into tail. Genital tube broad, initially composed of 3 rows of small, flattened cells. Ovary forming a loop around caudal organs, then from the level of the anterior margin of the caudal organ, the gonad is straight to the anterior, making a spermatheca a short distance from pharynx base ( Fig.1 A); spermatheca not distinctly offset, 20– 61 (38±16) µm long and 24–40 (30±6) µm wide. Uterus spacious, twisted, containing 19–27 (22±3) fully-formed eggs plus 2–5 immature eggs. Egg-shells ca.1 µm thick, very slightly tapered towards poles and evenly covered with tiny tubercles. Vulva situated at level of anterior third of body. No post-uterine sac present. Anterior vulva lip enlarged. Vagina straight, 12–37 (21±10) µm long. Caudal organs more than half-body length long, expanding from near the vulva to near the tail end; slit 391–547 (490±53) µm long and 14–20 (17±3) µm wide; total width 35–57 (48±8) µm ( Fig. 1. A, K; Fig. 2 A, G, H).

Females Males Holotype Paratypes Paratypes Male: Very similar to female in general appearance and morphology of anterior end and caudal organs but smaller by about half length and somewhat slimmer ( Fig. 1 B; Fig. 2 B). Body tapering anteriad from the level of pharynx base. Pharynx with corpus 47–72 (57±9) µm long and 8–10 (9±0.6) µm wide and basal bulb 17–24 (22±3) µm long and 17–28 (22±5) µm wide. Bulb more rounded than in females. Distal part of excretory cell nearly reaching tail end. Monorchic. Testis short, reflexed ventrally at 102–148 (117±17) µm from anterior end; reflexed section straight, 83–102 (91±8) µm long; posterior part of gonad coiled ( Fig. 1 J). Spermatocytes small, in 4 rows in distal region of gonad. Vas deferens and ejaculatory ducts difficult to trace because of coiled gonad. Cloacal aperture slightly elevated, just posterior to mid-body and surrounded by convex striated rim around 15 µm thick (pericloacal disk) ( Fig. 1 J; Fig. 2 F). No caudal sensilla present. Anterior margin of caudal organ at the level of cloacal aperture or slightly anterior to it, posterior margin near tail end, slit 140–188 (169±18) x 6–10 (7±2) µm with total width of caudal organ 20–37 (27±8) µm.

Type-material. Holotype female (on slide, accession No. 1246), paratype female (on slide, accession No. 1247), paratype male (on slide, accession No. 1252), and paratype male in copula with paratype female (on same slide, accession No. 1248), deposited in the Museum of the Helminthological Collections of the Centre of Parasitology at the Severtsov Institute of Ecology and Evolution, Moscow.

Type-host and locality. Megascolicidae gen. sp., Tinago Falls, Linamon, Lanao del Norte, Philippines (8º9'32''N, 124º11'11''E).

Etymology. The species name was constructed from the Visayan word ‘wati’ for an earthworm and Tinago for the location.

E

C 5

5

D

20

F 20

sp.

G I 40 t. int.

40

H 15

20 e.d.

e.g.

pcl.d.

K

A cl. J 20 B Abbreviations: cl., cloaca; c. o., caudal organ; e. p., excretory pore; pcl. d., pericloacal disc; v., vulva.

A B

50

C D

Diagnosis and relationships. The new species is distinctive in its small size, in the similarity in appearance of both sexes, in the characteristic body shape with tapering anterior and sausage-like posterior with a very short tip, in having very long caudal organs in the shape of slits or grooves, in the strongly curved pharynx, in the bubble-like conjunction between pharynx and intestine, in having coiled gonads in both sexes, in lacking an anus in females, in having the vulva at the level of the anterior third of body length and in having a pericloacal disk in males.

By its small body size, small cephalic hooks and the anterior position of the vulva S. watinagii sp. n. most closely resembles S. hirsutum and S. tuliemense . From the former it can be distinguished by its lack of setae, its different body shape in both sexes (not tapering towards posterior extremity vs tapering), its egg-shells being decorated differently (coated with tubercles vs cilia), its absence of an anus in females (vs an anus being present in S. hirsutum and S. tuliemense : although the anus was regarded as an additional excretory pore in the original description by Timm (1959) it was later recognized as an anus (Timm, 1966)), and its ovary having more numerous coils and a more spacious, looped uterus. S. watinagii sp. n. is close to S. tuliemense in having long slit-like caudal organs, but is distinguished by its different body shape in both sexes (not tapering towards the posterior extremity vs tapering), its shorter excretory duct which is mildly as opposed to heavily sclerotised, its indistinct amphids, and its pericloacal disk in males compared to a precloacal appendage. By its small size S. watinagii sp. n. is close to S. anseriforme and S. robustum but can be differentiated from both by its more anterior vulva position (30% vs 50- 60%).

From all the remaining species of the genus it differs in having a short, expanded body, more anterior position of vulva and smaller eggs without a polar cap or caps. From S. burmensis and S. philippinensis it differs additionally by its much smaller cephalic hooks and it differs from S. laotense , in having a pair of small hooks vs a single large hook. From S. anseriforme , S. hirsutum , S. laotense , S. modigliani , S. pingi , S. robustum , S. rodericensis , S. tsiliensis and S. tuliemense it differs in lacking an anus in females. From S. (= Siconemella ) burmensis , S. gatesi , S. hoplochaetellae , S. laotense , S. modigliani , S. pheretimae , S. pingi , S. robustum , S. rodericensis and S. tsiliensis it differs in lacking polar differentiation on egg-shells.

Figures

FIGURE 2. SEM images of Synoecnema watinagii sp. n. A, C, E, G, H, female; B, D, F, male. A: entire view (subventral); B: entire view (lateral); C: cephalic hooks (lateral); D: head end at the level of excretory pore (subventral); E: vulva region, lateral; F: male cloaca, lateral; G: middle part of caudal organ, lateral; H: margin of caudal organ, lateral. Scale bars: A, 100 Μm; B, 20 Μm; C, 3 Μm; D, 1 Μm; E, 5 Μm; F, 10 Μm; G, 5 Μm; H, 5 Μm.

Tables

TABLE 1. Morphometrics of Synoecnema watinagii sp. n. Measurements are in μm and in the form: mean ± standard error (range).

	Range	Mean	Range	Mean
n L 726	6 796–1,000	888 ± 66	6 415–478	457 ± 23
A 5.8	5.9–8.3	6.9 ± 9.8	5.3–7.1	6 ± 0.6
B 10	10.4–14.4	12.6 ± 1.3	6.1–7.8	6.8 ± 0.7
C			1.8–2.4	2.2 ± 0.2
V 31.5	29.4–34	31.5 ± 1.8
Maximum diameter 157	125–173	144 ± 18	65–90	78 ± 9
Anal diameter			65–90	77 ± 11.3
Pharynx length (straightened) 84	75–105	87 ± 10	70–95	80 ± 10
Distance from anterior extremity to 72 pharynx base	60–87	72 ± 11	59–78	68 ± 8
Distance from anterior extremity to 40 excretory pore	37–62	50 ± 8	38–54	45 ± 7
Distance from anterior extremity to 45 nerve ring	39–57	45 ± 8	32–50	42 ± 7
Tail length			175–248	212 ± 24
Egg length 40	40–43	41 ± 1
Egg diameter 21	22–23	23 ± 1