Deontolaimus uniformis ( Cobb, 1920 ) Cobb, 1920

Holovachov, Oleksandr & Boström, Sven, 2015, Swedish Plectida (Nematoda). Part 10. The genus Deontolaimus de Man, 1880, Zootaxa 4034 (1), pp. 1-44 : 10-13

Deontolaimus uniformis ( Cobb, 1920) comb. n.

( Fig. 5 ; Table 2 )

Material examined. Four males and one female (slides # 145492–145495) deposited in the general invertebrate collection of the Department of Zoology, Swedish Museum of Natural History, Stockholm, Sweden.

Habitat and locality. Sand and shells from 15–22 m deep, Bonden island in Skagerrak off the west coast of Sweden (N 58 12' 37'', E 11 18' 53''), 0 9 August 2011, legit O. Holovachov (two males); coarse gravel from 30–50 m deep, Skagerrak off the coast of Sweden (N 58° 17' 58'', E 11° 10' 05''), 0 9 August 2011, legit O. Holovachov (three males and one female).

Description. Adult. Body slender, cylindrical over most of its length, tapering anteriorly in anterior half of pharyngeal region and posteriorly on tail; strongly ventrally curved upon fixation, especially so in posterior part. Cuticle annulated; annules without ornamentation. Lateral field absent. Crystalloids absent. Body pores and epidermal glands absent. Somatic sensilla present, equally distributed along entire body; anterior-most somatic sensilla are located about two body diameters posterior to amphid. Labial region rounded, continuous with body contour; lips fused. Annulation along anterior-most part of body very weak; anterior-most annule appearing posterior to amphid and cephalic sensilla bases. One circle of labial sensilla visible on the anterior surface of labial region, they are small papilliform. Cephalic sensilla setiform, equal to 0.5–0.6 labial region diameter in length, their bases are located posterior to amphid. Subcephalic and cervical sensilla absent. Amphidial fovea ventrallyspiral, making at least two turns, located short distance anterior to cephalic sensilla bases. Ocelli absent. Nerve ring surrounding pharynx at anterior two-fifth of its length. Hemizonid not seen. Secretory-excretory system present; renette cell located on left-hand side of body along anterior part of intestine; it extends anteriorly along ventral side of pharynx and forms excretory ampulla just posterior to nerve ring level. Excretory canal weakly cuticularised, extends from excretory ampulla for a short distance and opens to exterior on ventral side, just posterior to nerve ring. Oral opening terminal. Buccal cavity uniformly tubular: cheilostom barrel-shaped; stegostom tubular, with large dorsal onchiostyle. Onchiostyle with bluntly rounded tip and subcylindrical body. Pharynx muscular in its anterior part and glandular in its posterior part, cylindrical anteriorly, expanding posteriorly; not subdivided into sections; without bulbs; valvular apparatus absent. Dorsal pharyngeal gland orifice opens at base of onchiostyle; orifices of subventral pharyngeal glands indistinct. Cardia short, embedded in intestine. Tail similar in shape in both sexes (more curved ventrad in male) elongate-conoid to subcylindrical, ventrally curved. Three caudal glands present, their nuclei are incaudal. Spinneret large conoid, with sclerotized distal part, functional.

Male. Reproductive system diorchic, both testes outstretched. Spicules paired, symmetrical, with arcuate subcylindrical shaft and small manubrium; manubrium is ventrally inclined. Gubernaculum present, plate-like, with paired dorsal apophysis. Alveolar supplements present along the entire body length, extending from anterior body end to cloaca, they are very small and located at the bottom of a narrow ventral groove. Tubular supplements absent. Midventral precloacal sensilla absent. Single postcloacal sensillum present, located subventrally at level of anterior two-fifth of tail length; sclerotized lamina absent. Tail with three pairs of papilliform sensilla: first (counting from cloaca) subventral pair located about one body diameter posterior to cloacal opening, second subventral pair located at posterior two-fifth of tail length, and third sublateral pair located at posterior one-fifth of tail length.

D. uniformis D. exilis

Recent specimens Cobb, 1920 Cobb, 1920 Blome, 1982 Female. Reproductive system didelphic, amphidelphic; ovary branches reflexed antidromously. Anterior genital branch 155 µm long (equal to 8.2% of total body length), located on right-hand side of intestine (n = 1), posterior genital branch 148 µm long (equal to 7.8% of total body length), located on left-hand side of intestine (n = 1). Oviduct short. Spermathecae indistinct. Uterus voluminous, filled with sperm. Vagina straight, 0.3 times vulval body diameter long. Epiptygmata, pars refringens vaginae and sensitive structures around vulva absent. Rectum 0.7 anal body diameter long.

Diagnosis. Deontolaimus uniformis ( Cobb, 1920) comb. n. is characterized by having body 1.8–2.4 mm long; anterior-most somatic sensilla located some distance posterior to amphid; cephalic sensilla equal to 0.5–0.6 labial region diameter in length; amphidial fovea ventrally-spiral with two turns, located short distance anterior to cephalic sensilla bases; excretory pore located just posterior to nerve ring level; onchiostyle with bluntly rounded tip and subcylindrical body; male with alveolar supplements extending from anterior end to cloaca, tubular supplements absent; spicules 43–46 µm long; and didelphic female reproductive system.

Relationships. Original description of this species is based on one female from the Atlantic coast of the USA. Swedish specimens agree with the original description in body size, shape of labial region, shape (with two turns) and position (anterior to cephalic sensilla bases) of amphid, relative length (equal to ≈ 0.5–0.8 labial region diameters) and position (some distance posterior to amphid) of labial sensilla, shape of onchiostyle, and shape of spinneret. The only morphometric difference between recent specimens and the female described by Cobb (1920) is the relative length of the tail (c' = 4.5 in Swedish specimens vs c' = 3.3 in type female), while the absolute tail length is almost the same (124 µm in Swedish female vs ≈ 120 µm in type female).

The recently collected population also closely resembles Deontolaimus exilis ( Cobb, 1920) comb. n. as described by Cobb (1920) in body size and other measurements, shape of labial region, and shape of amphid with two turns. Cobb described three minute supplementary organs located in front of cloaca. Males of recent specimens also have alveolar supplements in the same locations. The Swedish population differs from the original description of D. exilis in having shorter cephalic setae (equal to 0.5–0.6 labial region diameters in Swedish specimens vs equal to>1 labial region diameter in D. exilis ), shape of onchiostyle (without strongly sclerotized dorsal edge in Swedish specimens vs with strongly sclerotized dorsal edge in D. exilis ), alveolar supplements extending from anterior end to cloaca (vs present in front of cloaca only in D. exilis ), and longer tail (c' = 4.2–5.4 in Swedish specimens vs c' = 3.3 in D. exilis ). From the single female of D. exilis described from Germany by Blome (1982), our specimens differ in having shorter cephalic setae (6.5–8.5 µm Swedish specimens vs 18 µm in female from Germany), shorter onchiostyle (12–13 µm Swedish specimens vs 25 µm in female from Germany), and longer tail (c' = 4.2–5.4 in Swedish specimens vs c' = 3.4 in female from Germany).

Figures

FIGURE 5. Deontolaimus uniformis (Cobb, 1920) comb. n. male (C – F) and female (A – B, G – H). A & C: Anterior end, surface view; B & D: Anterior end, median section; E: Pharyngeal region, median section; F: Male posterior region; G: Female tail; H: Female reproductive system. Scale bar: A – H = 20 µm.

Tables

TABLE 2. Morphometrics of Deontolaimus uniformis (Cobb, 1920) comb. n. compared to D. exilis (Cobb, 1920) comb. n. based on literature data and specimens from the Swedish coast (all measurements are in µm, except for the ratios a, b, c, c', V, T, NR, EP). * Calculated from data in the original publication.

	4 ♂♂	1 ♀	1 ♀	1 ♂	1 ♀
Body length	1841–2396	1896	≈2400	≈2000	2075
a	53.7–85.4	40.9	50*	38.5*	53.2
b	7.7–9.8	7.7	5.9*	5.9*	8.0
c	13.0–16.5	15.3	20*	25*	21.2
c'	4.2–5.4	4.5	3.3*	2.5*	3.4
V(%) or T(%)	44.4–46.8	50.5	51	?	54
Body diameter	26–37	46	48*	52*	39
Pharynx length	225–289	248	408*	340*	261
Tail length	111–159	124	120*	80*	98
Anal or cloacal body diam.	27–32	27	36*	32*	29
Labial region diameter	13–15	13.5	?	?	10
Cephalic setae length	7–8.5	6.5	?	?	18
Setae bases from ant. end	8.5–9	8	?	?	?
Amphid from ant. end	1.5–2	1.5	?	?	1.5
Amphid width	4–5	4	?	?	?
Onchiostyle	12–12	13	?	?	25
Anterior-most body pore	41–42	41	?	?	?
Nerve ring from ant. end	90–116	108	?	?	?
NR (% of pharynx length)	39.9–41.9	43.6	?	?	?
Excretory pore from ant. end	91–124	110	?	?	116
EP (% of pharynx length)	40.4–43.3	44.5	?	?	44
Vagina length	–	12.1	?	–	?
Rectum length	–	19.3	?	–	?
Spicule length	43–46	–	–	?	–
Gubernaculum length	10–13	–	–	?	–
Apophysis length	6–6.5	–	–	?	–
Ant. alveolus from ant. end	27–30	–	–	?	–
Post. alveolus from post. end	8.5–16.5	–	–	?	–
Number of alveoli	≈190–255	0	0	present	0