Diplopeltoides pumilus ( Vincx & Gourbault, 1992 ) Holovachov & Boström, 2017

Holovachov, Oleksandr & Boström, Sven, 2017, Three new and five known species of Diplopeltoides Gerlach, 1962 (Nematoda, Diplopeltoididae) from Sweden, and a revision of the genus, European Journal of Taxonomy 369, pp. 1-35 : 20-22

Diplopeltoides pumilus ( Vincx & Gourbault, 1992) comb. nov.

Fig. 8 ; Table 5

Diagnosis

Diplopeltoides pumilus is characterised by by a body of 0.43–0.58 mm long; cuticle with longitudinal striation; cuticularised plate absent; cephalic sensilla setiform, 2–3 µm long; amphidial fovea an inverted U-shape, 8–17 µm long and 8–11 µm wide in female and 13–19 µm long and 8–9 µm wide in male; narrow space between amphidial branches not ornamented; secretory-excretory pore indistinct; tail conoid; testes opposed; spicules 24–27 µm long, strongly curved, with weakly defined manubrium and conoid shaft; gubernaculum plate-like, without apophyses.

Material examined

SWEDEN: 1 ♂, 1 ♀, Gullmarn Fjord near Fiskebäckskil, 58°15′13″ N, 11°27′31″ E, mud from 30–39 m deep, 21 Aug. 2010, M. Clément leg. (SMNH-159551); 1 ♂, Skagerrak, 58°20′06″ N, 11°09′24″ E, muddy sediment from 53 m deep, 9 Aug. 2011, O. Holovachov leg. (SMNH-159549); 2 ♀♀, Gullmarn Fjord near Fiskebäckskil, 58°15′09″ N, 11°27′54″ E, muddy sand from 8–15 m deep, 11 Aug. 2011, O. Holovachov leg. (SMNH-159550).

Description

Adult

Body cylindrical, posteriorly tapering in tail region, straight or curved upon fixation. Cuticle coarsely annulated along entire body, except for smooth anterior end (annulation starts at level of anterior ¼ of amphid) and terminal part of tail; annules 2.5 µm wide at mid-body region; longitudinal striation is distinct under light microscope, covers annules over entire body length. Somatic setae present on tail. Labial region bluntly rounded. Cuticularised plate underlying cephalic cuticle around amphid absent. Inner and outer labial sensilla not seen. Cephalic sensilla setiform, equal to 0.2–0.3 labial region diameters in length, their bases are located 2–5 µm from anterior end. Amphids similar in shape and size between sexes: amphidial fovea an inverted U-shape with branches equal in length. Narrow space between amphidial branches (amphidial shield) not cuticularised and not ornamented. Stoma very small, its cuticularised lining is uniform with lining of pharynx. Pharynx distinctly subdivided into anterior corpus and posterior postcorpus; corpus cylindrical or slightly fusiform, muscular; postcorpus consists of anterior narrow non-muscular isthmus and pear-shaped glandular basal swelling. Pharyngeal gland nuclei and orifices indistinct. Nerve ring surrounding isthmus. Secretory-excretory system indistinct. Tail conoid. Caudal glands opening via three separate openings, spinneret absent.

Female

Reproductive system didelphic, amphidelphic, reflexed; ovary branches symmetrical. Anterior ovary situated to either right or left of intestine; posterior ovary situated to either left or right of intestine. Vulva located immediately posterior to mid-body. Vagina straight, 0.2 of the vulval body diameter, with thick walls; pars refringens vaginae absent. Intrauterine egg not seen; sperm is sometimes visible in the uterus. Rectum short, 0.7–0.8 of corresponding body diameter long.

Male

Reproductive system diorchic, testes opposed: anterior testis outstretched and posterior testis reflexed. Spicules paired and symmetrical, strongly curved, with weakly defined manubrium and conoid shaft. Gubernaculum plate-like, without apophyses. Caudal setae present, arranged in subventral and subdorsal rows but difficult to observe and count.

Remarks

The recently collected population of D. pumilus is similar to the type specimen in general morphology and measurements, structure of cuticle and anterior end, differing only in the larger body size (0.50– 0.58 mm vs 0.29 mm in the type specimen), the longer amphid (16–19 µm vs 10 µm in the type specimen), the longer tail (c’= 4.0–4.5 vs c’= 3.5 in the type specimen) and the longer spicules (24–26 µm vs 19 µm in the type specimen). It is also similar to D. holovachovi from the Sea of Japan in general morphology, structure of cuticle and anterior end, except for the longer body (0.50–0.58 mm vs 0.43–0.50 mm in D. holovachovi ) and less pronounced sexual dimorphism in the shape of the amphid (more elongated in females vs more rounded in females from the type population).

Figures

Fig. 8. Diplopeltoides pumilus (Vincx & Gourbault, 1992) comb. nov. A. Female pharyngeal region, optical median section. B. Female tail. C. Female anterior end, surface view. D. Male tail. E. Male anterior end, surface view. F. Vulval region. Scale bar = 20 µm.

Tables

Table 5. Measurements (in µm) of Diplopeltoides pumilus (Vincx & Gourbault, 1992) comb. nov., presented as mean and (range) for females and and each male individual measurement separated with a semicolon; “?” indicates that the character can not be observed or measured.

Sex	Female	Male
Number of specimens	3	2
Body length	543 (520–564)	504; 578
Body diameter (BD)	36 (32–38)	22; 28
Pharynx length	115 (107–121)	121; 119
Tail length	81 (77–85)	77; 91
Anal body diameter (ABD)	20 (19–21)	17; 21
a	15.3 (14.6–16.4)	22.8; 20.4
b	4.7 (4.6–4.9)	4.2; 4.8
c	6.7 (6.6–6.8)	6.5; 6.3
c’	4.0 (4.0–4.1)	4.5; 4.4
V or T (%)	52.4 (52.1–52.9)	?; 44.5
Labial region diameter	10.4 (10.0–12.0)	8.0; 10.5
Cephalic setae length	2.5 (2.0–3.0)	3.0; 2.0
Amphid from anterior end	6.7 (6.0–7.0)	6.0; 5.0
Dorsal amphid branch length	16.3 (16.0–16.5)	19.0; 16.0
Ventral amphid branch length	16.1 (15.0–16.5)	19.0; 16.0
Amphid width	9.0 (7.5–10.5)	9.0; 8.0
Nerve ring from anterior end	65 (62–68)	65; 68
Nerve ring from anterior end as % of pharynx length	58 (56–58)	53; 57
Anterior gonad length (to flexure)	107 (95–130)	–
Posterior gonad length (to flexure)	97 (77–119)	–
Vagina or spicules length	8 (7–9)	24; 26
Rectum or gubernaculum length	14 (14–15)	4; 8
Vagina length / BD	0.2	–
Rectum or spicules / ABD	0.7 (0.7–0.8)	1.4; 1.3