Setostephanolaimus tchesunovi, Holovachov, Oleksandr, 2014

Holovachov, Oleksandr, 2014, Swedish Plectida (Nematoda). Part 7. Setostephanolaimus tchesunovi sp. n. from the west coast of Sweden, Zootaxa 3847 (4), pp. 576-582 : 577-579

Setostephanolaimus tchesunovi sp. n.

( Fig. 1 ; Table 1 )

Type material. Holotype male (slide # Type-8666), as well as four male and five female paratypes (slides # Type- 8667–Type-8670) deposited in the invertebrate type collection of the Department of Zoology, Swedish Museum of Natural History, Stockholm, Sweden.

Type locality. Gravel, mud and algae from 30–70 m deep, Skagerrak off the coast of Sweden (N 58° 22' 14'', E 11° 05' 00''), 0 9 August 2011, legit O. Holovachov (one male).

Additional locality. Muddy sand from 8–15 m deep, Gullmarn Fjord near Fiskebäckskil, Sweden (N 58° 15' 09'', E 11° 27' 54''), 11 August 2011, legit O. Holovachov (four males and five females).

Etymology. The species is named in honour of Prof. A.V. Tchesunov, a well-known Russian nematologist, who, among other things, proposed the genus Setostephanolaimus .

Description. Adult. Body more or less cylindrical, tapering anteriorly in pharyngeal region and posteriorly on tail, ventrally curved upon fixation, more strongly curved ventrad in posterior part in males. Cuticle annulated; annuli 2.0–2.5 µm wide at mid-body, without ornamentation. Lateral field absent. Small body pores present, arranged sublaterally along the entire body. Anteriormost body pore located somewhat posterior to amphid. Labial region rounded, continuous with the body contour, lips fused. First annulus appears posterior to the amphid, 9–16 µm from anterior end. Inner labial sensilla indistinct. Outer labial sensilla setiform, located on the anterior surface of lips, 1–2 µm from anterior end. Cephalic sensilla setiform, equal to 0.9–1.3 labial region diameters in length, located 2–5 µm from anterior end. Subcephalic sensilla present, setiform, located in ventro-sublateral position 3–5 µm from anterior end. Amphidial fovea transversely ovoid, 3–3.5 µm wide. Nerve ring surrounding pharynx at about middle of its length. Hemizonid not seen. Secretory-excretory system present; renette cell elongate, with granular cytoplasm, located posterior to the pharynx base, extending along the anterior part of intestine. Excretory pore located mid-distance between the nerve ring and pharynx base. Buccal cavity narrow, funnel-shaped, undifferentiated. Pharynx cylindrical anteriorly, gradually narrowing posteriorly to nerve ring and widening again into pear-shaped basal expansion; muscularised with uniformly thickened lumen along its anterior part, mostly glandular in its posterior part. Nucleus of dorsal pharyngeal gland distinct in some specimens, located within the dorsal sector of the basal expansion. Cardia 12–25 µm long, conoid, its posterior part embedded in intestine. Tail elongate-conoid, arcuate ventrad. Three caudal glands present, their nuclei are incaudal. Spinneret functional.

Male. Reproductive system monorchic, single anterior testis outstretched. Spicules paired, symmetrical, with thin arcuate shaft and hemispherical manubrium. Gubernaculum present, wedge-shaped, with double dorsal apophysis. Accessory apparatus composed of one midventral precloacal papilliform sensillum located anterior to cloaca, at mid-distance between cloaca and posteriormost tubular supplement; 6–9 evenly spaced midventral tubular supplements extending for 127–171 µm from cloaca towards anterior end; posteriormost tubular supplement located 37–44 µm from cloaca. Tubular supplements straight, with hook like protruding distal part with biacute tips. Alveolar supplements absent. Precloacal subventral sensilla absent. Caudal setiform sensilla present, 12–15 in number, arranged in subventral and subdorsal raws.

Female. Reproductive system pseudomonodelphic, opisthodelphic: anterior ovary reduced, non-functional; posterior ovary branch reflexed antidromously. Anterior genital branch 100–169 µm long (equal to 8.3–13.9% of total body length), located on either right or left-hand side of intestine, often filled with spermatozoa; posterior genital branch 179–293 µm long (equal to 15.2–24.7% of total body length), located on either left or right-hand side of intestine. Oviduct a broad tube. Spermatheca as separate structure absent. Uterus a wide tube composed of large cells. Vagina straight, 0.3–0.5 vulval body diameters in length; pars proximalis vaginae encircled by single sphincter muscle; pars refringens vaginae absent. Epiptygmata and sensitive structures around vulva (advulval sensilla) absent. Single intrauterine egg measuring 99x25 µm. Rectum 1.4–1.5 anal body diameters long; surrounded by three gland-like cells at intestine-rectum junction.

Diagnosis. Setostephanolaimus tchesunovi sp. n. is particularly characterised by 1.0– 1.3 mm long body, outer labial setae 6.5–8.5 µm long, cephalic setae 9–11 µm long, subcephalic setae 4–6 µm long, transversely ovoid amphid, female with monodelphic opisthodelphic reproductive system, male with 6–9 tubular and without alveolar supplements, spicules arcuate and 54–64 µm long, gubernaculum with dorsal apophysis.

Relationships. In having distinct subcephalic setae and opisthodelphic female reproductive system, the new species can be separated from all but three species of the genus Setostephanolaimus : S. bicoronatus ( Boucher & Helléouët, 1977) Tchesunov, 1994, S. orientalis Fadeeva & Mordukhovich, 2007 and S. spartinae . The new species can be separated from S. bicoronatus by longer spicules (54–64 µm vs. 30–38 µm in S. bicoronatus ) and shape of gubernaculum (with dorsal apophysis vs. with caudal apophysis in S. bicoronatus ). From S. orientalis it differs in longer spicules (54–64 µm vs. 36 µm in S. orientalis ) and shorter cephalic setae (9–11 µm vs. 14 µm in S. orientalis ), and from S. spartinae in longer spicules (54–64 µm vs. 17–20 µm in S. spartinae ) and shape of gubernaculum (with dorsal apophysis vs. with caudal apophysis in S. spartinae ). In having long spicules and opisthodelphic female reproductive system, the new species also closely resembles S. longispiculum ( Vadhyar, 1981) Tchesunov, 1994 . Nonetheless, both species can be easily separated by their body length (1.0– 1.3 mm in S. tchesunovi sp. n. vs. 1.7–2.1 mm in S. longispiculum ), length of outer labial (6.5–8.5 µm in S. tchesunovi sp. n. vs. 11–13 µm in S. longispiculum ) and cephalic (9–11 µm in S. tchesunovi sp. n. vs. 15–19 µm in S. longispiculum ) seetae, presence of subcephalic setae (present in S. tchesunovi sp. n. vs. absent in S. longispiculum ) and number of tubular supplements (6–9 in S. tchesunovi sp. n. vs. 12–15 mm in S. longispiculum ). Further characters summarising the differences between all species of the genus Setostephanolaimus are given in Table 2.

Figures

FIGURE 1. Setostephanolaimus tchesunovi sp. n., holotype male (A – C) and paratype female (D – F). A: Pharyngeal region; B: Male caudal region; C: Anterior end, surface view; D: Female tail; E: Anterior part of the female reproductive system; F: Posterior part of the female reproductive system. Scale bar: A – E = 20 µm.

Tables

TABLE 1. Morphometrics of Setostephanolaimus tchesunovi sp. n. (all measurements are in µm, except for the ratios a, b, c, c', V and T).

Character	Holotype, male	Males (n=5, incl. holotype)	Females (n=5)
Body length	1169	1151±73 (1059–1259)	1174±53 (1083–1217)
a	48.1	54.5±4.1 (48.1–58.8)	48.5±2.8 (44.9–52.7)
b	5.3	5.7±0.4 (5.3–6.5)	5.6±0.3 (5.3–6.0)
c	9.6	10.5±0.8 (9.5–11.4)	10.9±0.6 (10.2–11.6)
c'	6.1	5.5±0.5 (5.0–6.1)	6.8±0.9 (6.1–8.3)
V or T (%)	?	?	40.3±2.5 (37.1–43.0)
Body diameter	24.0	21.2±1.7 (19.0–24.0)	24.3±2.0 (22.0–27.0)
Pharynx length	216	203±17 (180–220)	209±8 (199–217)
Tail length	122	110±8 (101–122)	108±9 (93–116)
Anal or cloacal body diameter	20.0	19.9±0.9 (18.5–21.5)	15.9±2.1 (13.5–18.0)
Labial region diameter	10.0	9.5±0.4 (9.0–10.0)	9.6±0.8 (8.5–11.0)
Outer labial setae length	7.0	7.5±0.7 (6.5–8.5)	7.0±0.6 (6.5–8.0)
Cephalic setae length	9.0	10.2±0.6 (9.0–11.0)	10.3±0.4 (10.0–11.0)
Subcephalic setae length	6.0	5.2±0.6 (4.0–6.0)	4.8±0.4 (4.0–5.0)
Amphid position from ant. end	5.0	8.3±1.7 (5.0–9.0)	8.9±1.3 (7.0–10.0)
Stoma length	3.0	3.0±0.7 (2.0–3.5)	2.5±0.5 (2.0–3.0)
Nerve ring from ant. end	107	102±9 (92–115)	103±6 (94–111)
NR (%)	48.7	50.8±1.5 (48.7–52.1)	49.3±1.8 (47.4–51.3)
Excretory pore from ant. end	144	144	137±3 (133–140)
EP (%)	65.8	65.8	66.3±2.1 (63.4–69.1)
Vagina length	-	-	10.0±2.0 (7.0–12.0)
Rectum length	-	-	21.6±3.0 (19.0–25.0)
Spicule length	55.0	58.8±4.0 (54.0–63.5)	-
Gubernaculum length	11.0	10.7±1.0 (9.0–12.0)	-
Apophysis length	5.0	5.0±0.5 (4.0–6.0)	-
Precloacal sensilla from cloaca	21.0	23.8±2.9 (20.0–26.5)	-
Tubular supplements	8	6–9	0