Rhadinema timmi ( Vitiello, 1971 ) Vitiello, 1971

Holovachov, Oleksandr & Boström, Sven, 2014, Swedish Plectida (Nematoda). Part 5. Rhadinema timmi (Vitiello, 1971) comb. n., Zootaxa 3779 (4), pp. 477-486 : 478-483

Rhadinema timmi ( Vitiello, 1971) comb. n.

( Figs 1–3 , 4 A–E, 5 A & C; Tables 1 & 2 )

Material examined. 31 males and 25 females (slides # 128858-128862, 133259-133266) deposited in the general invertebrate collection of the Department of Zoology, Swedish Museum of Natural History, Stockholm, Sweden.

Habitat and locality. Mud from 30–39 m deep, Gullmarn Fjord near Fiskebäckskil, Sweden (N 58° 15' 13'', E 11° 27' 31''), 21 August 2010, legit M. Clément (eight males and four females); muddy sediment from 53 m deep, Skagerrak, off the coast of Sweden (N 58° 20' 06'', E 11° 09' 24''), 0 9 August 2011, legit O. Holovachov (one female); muddy sand 8–15 m deep, Gullmarn Fjord near Fiskebäckskil, Sweden (N 58° 15' 09'', E 11° 27' 54''), 11 August 2011, legit O. Holovachov (11 males and 14 females); soft mud from 44 m deep, Gullmarn Fjord near Fiskebäckskil, Sweden (N 58° 15' 37'', E 11° 27' 43''), 11 August 2011, legit O. Holovachov (one male); soft bottom 352–374 m deep, Skagerrak, Sweden (N 58° 19' 15.6'' –20.9'', E 10° 29' 33.5'' –34.0''), 10 September 2012, legit "Inventering Bratten" expedition (4 females and 2 males); soft bottom 221–260 m deep, Skagerrak, Sweden (N 58° 28' 28.0'' –31.1'', E 10° 33' 19.1'' –23.80''), 11 September 2012, legit "Inventering Bratten" expedition (2 females and 4 males); soft bottom 232–240 m deep, Skagerrak, Sweden (N 58° 27' 36.7'' –43.3'', E 10° 32' 52.0'' –59.4''), 12 September 2012, legit "Inventering Bratten" expedition (5 males).

Description. Adult. Body cylindrical over most of its length, tapering anteriorly in pharyngeal region and posteriorly on tail; straight or curved ventrad upon fixation, more strongly curved ventrad in posterior part in males. Maximum body diameter at vulva in female; male body more cylindrical, with cloacal body diameter the same or somewhat bigger than the diameter at midbody. Cuticle thin and weakly annulated; annuli poorly discernible under the light microscope, without ornamentation. Lateral field absent. Prominent body pores present, arranged in sublateral rows in close pairs on each body side; usually 6–7 body pores are present along each side of pharyngeal region; several body pores scattered over rest of the body. Anteriormost body pore located at level of stoma, just posterior to amphid. Labial region rounded, continuous with body contour, lips fused. Inner labial sensilla indistinct. Outer labial sensilla indistinct under the light microscope, small pore-like as seen under SEM; located on the anterior surface of lips. Cephalic sensilla setiform, equal to 0.3–0.6 of labial region diameter. Subcephalic and cervical sensilla, and ocelli absent. Amphidial fovea round, located at level of middle of stoma. One male specimen with two amphidial foveae on one body side ( Fig. 4 D) and normal structure on the other side ( Fig. 4 C). Nerve ring surrounding pharynx at level of anterior part of isthmus. Hemizonid not seen. Secretoryexcretory system present, excretory pore located just posterior to nerve ring, renette cell obscure. Buccal cavity uniformly tubular: cheilostom short, with six weakly cuticularised longitudinal rugae; gymnostom short, sclerotized, with bar-shaped rhabdia; stegostom long, tubular, with uniformly thickened lumen. Pharynx muscular, cylindrical anteriorly, with weak basal expansion; basal bulb and valvular apparatus absent. Anterior cylindrical part of pharynx subdivided by breaks in muscular pharyngeal tissue into cylindrical procorpus, cylindrical metacorpus and narrow isthmus. Pharyngeal glands and their orifices indistinct. Cardia short, cylindrical, its posterior part embedded in intestine. Tail almost similar in shape in both sexes (shorter and more curved ventrad in male), elongate-conoid, with subcylindrical distal portion. Three caudal glands present, their nuclei are incaudal. Spinneret functional.

Male. Reproductive system diorchic; both testes outstretched. Spicules paired, symmetrical, with arcuate cylindrical calamus and ovoid manubrium; velum present, broad. Gubernaculum plate-like, with long caudal apophysis and short caudal projection located closer to the ventral body side. Accessory apparatus composed of one midventral precloacal papilliform sensillum located anterior to cloaca, at mid-distance between cloaca and posteriormost tubular supplement; 10–11 evenly spaced midventral tubular supplements extending for 300–353 µm from cloaca towards anterior end; alveolar supplements absent. Tubular supplements straight, complex in shape, with blunt tips. Posteriormost tubular supplement 42–45 µm anterior to cloaca, anterior to spicules. Precloacal subventral sensilla absent. Caudal setiform sensilla present, 6–8 pairs arranged as follows: 3–5 subventral pairs along the anterior to middle part of tail, one subdorsal, one subventral and another one subdorsal pair towards tail tip. One pair of subventral papilliform sensilla located at about anterior one-third of tail, posterior to the first or second (anteriormost) pair of caudal setiform sensilla.

Female. Reproductive system didelphic, amphidelphic; ovary branches reflexed antidromously. Anterior genital branch 197–307 µm long (equal to 12.1–18.2% of total body length), located on right-hand side of intestine (n=6), posterior genital branch 183–335 µm long (equal to 11.5–20.2% of total body length), located on left-hand side of intestine (n=6). Oviduct a narrow tube. Spermathecae as separate structures indistinct. Uterus a wide and long tube. Vagina straight, 0.3–0.5 times vulval body diameters long; pars proximalis vaginae encircled by single sphincter muscle; pars refringens vaginae absent. Vulva midventral, a transverse slit with small wrinkled lips as seen under SEM. Epiptygmata absent. Two small subventral sensillae are seen under SEM, one on each side of the vulva ( Fig. 2 F), however, they are indistinct under the light microscope. Rectum 1.1–1.5 anal body diameters long; surrounded by gland-like cells at intestine-rectum junction.

Diagnosis (supplemented with literature data). Rhadinema timmi is particularly characterised by the 1.3–1.8 mm long body; rounded labial region weakly offset from body contour; cephalic setae 2–4 µm long; amphid located 12–19 µm from anterior end; first body pore located 22–30 µm from anterior end; lateral field absent; stoma tubular: cheilostom with six weakly cuticularised longitudinal rugae, gymnostom with sclerotized barshaped rhabdia, stegostom long, tubular; female without supplements, vagina without pars refringens, vulva midventral; male with 10–11 tubular and without alveolar supplements; spicules arcuate and 21–30 µm long.

Remarks. Current specimens agree well with the type specimens of R. timmi in general morphology, body size, measurements, shape of anterior end and amphids, number and shape of supplements, shape of spicules and gubernaculum. The only differences are a slightly longer and plumper body in females (L= 1534–1759 µm vs. L= 1438–1595 µm in type specimens; a=55.1–70.4 vs. a= 71.9–88.6 in type specimens), somewhat longer tail in both males (135–148 µm vs. 120–130 µm in type specimens) and females (149–162 µm vs. 145–151 µm in type specimens), somewhat longer stoma (31–36 µm vs. 27 µm in type specimens) and slightly longer spicules (23.5– 30.0 µm vs. 21.0–23.0 µm long in type specimens). Vitiello (1971) did not describe longitudinal rugae in the cheilostom in his specimens, but they are rather obvious in his drawings ( Vitiello, 1971: Fig. 5 a–b). Unfortunately, the original description of this species is not complete enough to allow any further comparisons.

Systematic position. This species fits within the diagnosis of the genus Rhadinema and of the family Rhadinematidae Lorenzen, 1981 but does not fit within the diagnosis of the genus Leptolaimus de Man, 1876 and of the family Leptolaimidae Örley, 1880 based on the following features: cheilostom with six longitudinal rugae (vs. without rugae in Leptolaimus ), lateral field absent (vs. present in Leptolaimus ), precloacal sensilla located middistance between the posteriormost supplement and cloacal opening (vs. on the anterior cloacal lip in Leptolaimus ); precloacal subventral setiform sensilla absent (vs. present in Leptolaimus ).

R. timmi can be easily distinguished from the type and only other known species of the genus Rhadinema , R. flexile ( Figs 4 F–H, 5 B & D) in a number of morphological and morphometric characters ( Cobb, 1920; Lorenzen, 1972; Holovachov & Boström, 2004; Holovachov, 2006): narrower labial region (5.0–8.0 µm vs. 10.0–13.0 µm in R. flexile ), smaller stoma (vs. stoma bigger and more spacious in R. flexile , see Fig. 4 F), absence of sublateral sensilla around the vulval region in females (vs. present in R. flexile , see Fig. 4 H), more anterior position of vulva (V=47–50% vs. V=59% in R. flexile ), less arcuate spicules, different shape of gubernaculum (caudal apophyses cup-shaped in R. flexile ), and longer tail (c'=6.9–10.8 vs. c'= 5.1–7.2 in R. flexile ).

Figures

FIGURE 1. Rhadinema timmi (Vitiello, 1971) comb. n., male (A – C) and female (D – E). A: Pharyngeal region, median section; B: Anterior end, surface view; C: Male posterior region; D: Female vulval region; E: Female tail. Scale bar: A – E = 20 µm.

FIGURE 2. Rhadinema timmi (Vitiello, 1971) comb. n., male (A – E) and female (F – I). A: Anterior end, apical view; B: Anterior end, lateral view, ventral to the right; C: Anterior end, lateral view, ventral to the left; D: Anterior end, subventral view; E: Excretory pore (arrow); F: Female vulval region, ventral view showing subventral sensillae (arrows); G: Spinneret; H – I: Tail. Scale bars: A, E – G = 5 µm, B – D = 10 µm; I – H = 50 µm.

FIGURE 3. Rhadinema timmi (Vitiello, 1971) comb. n., male (A – E). A: Posterior region, subventral view (arrow and arrowhead as in D); B: Cloacal region, lateral view with protruding spicules; C: Caudal region, lateral view; D: Posteriormost supplement (arrow) and precloacal papilliform sensillum (arrowhead); E: Caudal sensillum (arrow). Scale bars: A – B = 20 µm, C = 50 µm; D – E = 10 µm.

FIGURE 4. Rhadinema timmi (Vitiello, 1971) comb. n., male (A – E), and Rhadinema flexile Cobb, 1920, female (F, H) and male (G). A, G: Anterior end, surface view; B, F: Stoma; C, D: Anterior end, amphid variability in the same specimen; E: Pharynx base; H: Advulval sensilla. Scale bars: A – H = 10 µm.

FIGURE 5. Rhadinema timmi (Vitiello, 1971) comb. n., male (A) and female (C), and Rhadinema flexile Cobb, 1920, male (B) and female (D). A – B: Caudal region; C – D: Vulval region. Scale bars: A – D = 10 µm.

Tables

TABLE 1. Morphometrics of Rhadinema timmi (Vitiello, 1971) comb. n. from the Swedish west coast compared to type specimens from the Mediterranean (all measurements are in µm, except for the ratios a, b, c, c', V, NR).

	Recent specimens from Gullmarn Fjord	Types (after Vitiello, 1971)
	6 ♂♂ 6 ♀♀	3 ♂♂ 2 ♀♀
Body length	1490±39 (1448–1531) 1657±84 (1534–1759)	1295–1548 1438–1595
a	81.5±3.8 (75.1–85.7) 63.3±5.6 (55.1–70.4)	70.0–78.4 71.9–88.6
b	9.9±0.3 (9.3–10.3) 10.8±0.2 (10.5–11.0)	10.0–10.6 9.2–11.8
c	10.6±0.3 (10.3–11.1) 10.7±0.4 (10.1–11.4)	10.7–12.2 9.9–10.5
c'	7.3±0.3 (6.9–7.6) 10.1±0.6 (8.9–10.8)	7.3–7.6 10.4–10.8
V (%)	- 47.9±0.6 (47.3–49.1)	- 49–50
Body diameter	18.3±1.0 (17.0–19.0) 26.3±2.1 (23.5–29.0)	18.5–20.0 18.0–20.0
Pharynx length	151±5 (144–158) 154±7 (147–165)	129–150 134–155
Tail length	140±4 (135–148) 155±5 (149–162)	120–130 145–151
Anal or cloacal body diam.	19.3±0.9 (18.5–21.0) 15.3±1.0 (15.0–17.0)	16.5–17.0 14.0
Labial region diameter	6.7±0.4 (6.5–7.0) 7.3±0.3 (7.0–8.0)	5.0–7.0 6.0–6.5
Cephalic setae length	2.6±0.6 (2.0–3.5) 2.9±0.8 (2.0–4.0)	2.6
Amphid from ant. end	15.4±2.0 (12.0–18.0) 17.0±1.2 (16.0–19.0)	13.0
Amphid width	5.1±0.5 (4.0–6.0) 4.8±0.4 (4.0–5.0)	5.2
First body pore	24.8±2.9 (22.0–28.5) 28.6±1.3 (26.5–30.0)	?
Stoma length	32.6±1.5 (31.0–35.0) 34.4±1.2 (33.0–36.0)	27.0
Procorpus length	22.5±2.4 (20.5–27.0) 22.5±1.5 (21.5–25.0)	?
Metacorpus length	25.9±2.4 (24.0–31.0) 25.3±1.4 (24.0–27.0)	?
Isthmus length	54.1±4.6 (48.0–59.0) 52.9±4.6 (46.5–58.0)	?
Bulbus length	16.1±1.0 (15.0–17.0) 18.9±3.8 (15.0–25.0)	?
Nerve ring from ant. end	86.3±2.1 (84.0–88.5) 89.1±3.1 (86.0–94.0)	?
NR (%)	56.7±1.0 (55.4–57.7) 57.7±1.1 (56.5–58.9)	55.0
Vagina length	- 10.1±0.8 (8.5–11.0)	-?
Rectum length	- 19.5±2.0 (17.0–23.0)	-?
Spicule length	26.7±3.2 (23.5–30.0) -	21.0–23.0 -
Tubular supplements	10–11 -	10–11 -

TABLE 2. Selected diagnostic characters of species of the genus Rhadinema Cobb, 1920 based on literature data supplemented with recent observations (all measurements are in µm, except for the ratios a, b, c, c', V). Main morphometric differences between the two species are highlighted by figures in bold font.

Body length	Rhadinema timmi (Vitiello, 1971) comb. n. 1295–1759	Rhadinema flexile Cobb, 1920 1400 –2157
a b c	55.1–88.6 9.2–11.8 9.9–12.2	66.9–78.0 10.2–12.9 13.7–15.5
c' V (%) Body diameter	6.9–10.8 47.3–50.0 17.0–29.0	5.1–7.2 58.9 20.0–32.0
Stoma length Pharynx length Tail length	27.0–36.0 129–165 120–162	18.0–21.5* 130.0–168.0 100.0–144.5
Anal or cloacal body diam. Labial region diameter Cephalic setae length	14.0–21.0 5.0–8.0 2.0–4.0	18.0–22.0 10.0–13.0 5.5
Amphid from ant. end Amphid width First body pore	12.0–19.0 4.0–6.0 22.0–30.0	10.0–11.0 5.0–7.0 12.0–13.0
Vagina length Rectum length Spicule length	8.5–11.0 17.0–23.0 21.0–30.0	12.0 22.0 18.0–25.5
Tubular supplements	10–11	7–10
* new data for two specimens from Germany.