Cephalobus topali Andrássy, 1970

Nguyen, Thi Anh Duong, Bonkowski, Michael, Peña-Santiago, Reyes & Abolafia, Joaquín, 2016, Re-description of Cephalobus topali Andrássy, 1970 (Rhabditida, Cephalobidae) from Vietnam, and transfer to Acrobeloides (Cobb, 1924) Thorne, 1937, Zootaxa 4092 (4), pp. 593-600 : 594-599

Cephalobus topali Andrássy, 1970

( Figs 1–3 )

Material examined. Six females and eight larvae from Pia Oac, Vietnam, in acceptable state of preservation.

Morphometrics. See Table 1 .

Description. Female: Body 0.31–0.35 mm long. Habitus straight or sigmoid after fixation. Cuticle distinctly annulated, annuli 2 mm thick at mid-body. Lateral field occupying 15–24% of mid-body diameter, with two alae (three or four longitudinal incisures, depending on either alae are slightly separate or not) arising at pharyngeal corpus level and fading away at phasmid level, appearing only one incisure posteriorly. With SEM, anterior region seen to comprise three pairs of asymmetrical conoid lips, and three low and rounded labial probolae separated from the corresponding pair of lips by an incisure; primary axils deep, U-shaped, lacking guard processes; secondary axils shallow, V-shaped, lacking guard processes. Sensillae papilliform, six labial and four cephalic. Amphids slitlike, with thickened margin. Stoma cephaloboid: cheilostom with rounded rhabdia; gymnostom narrower than cheilostom, and as wide as stegostom, the latter with small rhabdia. Pharynx also cephaloboid: slightly fusiform corpus, 2.6–3.1 times the isthmus length, with procorpus longer than metacorpus; isthmus narrower than corpus; basal bulb pyriform, bearing well developed valves at its middle. Cardia hemispheroid, surrounded by intestinal tissue. Intestine lacking specialization; its lumen often sigmoid. Nerve ring located at 56–76% of neck (stoma + pharynx) length, at level of the posterior part of corpus, near its junction to isthmus. Excretory pore at 61–87% of neck length, 44–48 annuli from the anterior end, at level of corpus-isthmus junction, in front of hemizonid. Deirid at 63–81% of neck length, 49–53 annuli from the anterior end, at level of basal bulb. Reproductive system monodelphic-prodelphic: ovary posteriorly directed, with or without a double flexure posterior to vulva level; oviduct short, difficult to distinguish; spermatheca poorly developed, 0.3–0.4 times the corresponding body diameter in length; uterus tube-like, as long as the corresponding body diameter, consisting of a shorter proximal part with thin walls and distinct lumen and a longer distal section having thick walls and small lumen; post-vulval sac 0.2–0.4 times the corresponding body diameter in length; vagina extending inwards to one-third of body diameter. Rectum 1.3–1.7 anal body widths in length. Tail conoid, with 11–13 annuli on the ventral side; terminus rounded, ending in an acute or wart-shaped mucro. Phasmid situated at 29–34% of tail length.

Male: Unknown.

Diagnosis (based on the 6 specimens studied). This species is characterized by its body length (306–347 µm in females), lateral field with two alae or 3–4 longitudinal incisures, lip region with three pairs of asymmetrical conoid lips, three low and rounded labial probolae separate from the corresponding pair of lips by an incisure, Ushaped primary axils without guard processes, V-shaped secondary axils without guard processes, pharyngeal corpus slightly fusiform and 2.6–3.1 times the isthmus length, spermatheca and post-vulval sac poorly developed, female tail conoid (18–24 µm, c = 12.7–17.0, c’ = 1.8–2.7) with rounded terminus ending in an acute or wartshaped mucro, and phasmid at 29–34% of tail length. Males are unknown.

Locality and habitat. Pia Oac (GPS coordinates: 22º36'28''N and 105º52'15''E, elevation 1150 m), Cao Bang Province, Vietnam, collected from the rhizosphere of Zea mays L. growing in an area of intensive agricultural crops alongside the Pia Oac Natural Reserve.

* Measurements from drawings, ** from other measurements.

Discussion. Cephalobus topali was originally described from only one female and three larval specimens. The material herein studied perfectly fits Andrássy’s (1970) description. The SEM observations reported here provide additional information that raises doubt about the position of this species. For example, instead of connecting the corresponding adjacent pairs of lips, a typical diagnostic feature of the genus Cephalobus Bastian, 1865 (see Abolafia & Peña-Santiago 2009), the labial probolae of the specimen examined here are clearly separated from the lips by an incisures ( Fig. 3 A–C). This fits the pattern observed in representatives of the genus Acrobeloides (Cobb, 1924) Thorne, 1937 (see Abolafia & Peña-Santiago, 2003). Consequently, this species is transferred to the genus Acrobeloides as A. topali (Andrássy, 1970) comb n.

Andrássy (1984) regarded C. topali as identical to and a junior synonym of Cephalobus quadrilineatus Eroshenko, 1968 , only known to occur in Russian Far East Territories. Both species have similar morphology and morphometry (see comparison in Table 1 ), and both have an acute mucro at the tail tip. Later, however, Andrássy (2005) maintained both species as valid, but examination of specimens of the Russian species is necessary to confirm it. Provisionally, we accept that the two species are valid as differences between them were noted: isthmus size (as long as vs one-third of the corresponding body diameter), excretory pore location (at level of the corpusisthmus junction vs at isthmus posterior portion, near the basal bulb), presence of a short vs absence of a postvulval sac, and rectum length (as long as vs shorter than the corresponding body diameter).

The distribution of A. topali appears to be restricted to the north of Vietnam, associated with modified soils. Andrássy (1970) found it among grass roots in the municipal cemetery of the district of Yen So (Hanoi), and here it is reported from further north, in agricultural plots opened in the rain forest, close to the Pia Oac Natural Reserve. In the last two years, several hundred specimens of nematodes have been examined from this area but, only a few specimens of this rare species were found, and none came from natural, unaltered areas.

Figures

FIGURE 1. Acrobeloides topali (Andrássy, 1970) n. comb. (female, in lateral view). A: Anterior end. B: Lip region. C, D: Reproductive system. E: Lateral field. F: Entire female. G – I: Posterior end.

FIGURE 2. Acrobeloides topali (Andrássy, 1970) n. comb. (female, light micrographs). A: Anterior end (white arrow indicates the excretory pore, black arrow pointing at the deirid). B: Stoma. C: Hemizonid (arrowed). D: Reproductive system. E, F, H: Tail (arrows pointing at the phasmid). G: Deirid (arrowed). I, J: Lateral field.

FIGURE 3. Acrobeloides topali (Andrássy, 1970) n. comb. (female, scanning electron micrographs). A – D: Lip region (right lateral, left subventral, frontal and right subventral, respectively). E: Lateral field. F, G: Posterior end (arrows indicate the phasmid).

Tables

TABLE 1. Morphometrics of Cephalobus quadrilineatus Eroshenko, 1968 and C. topali Andrássy, 1970. Measurements in Μm and in the form: mean ± standard deviation (range) where appropriate.

Species Locality/District Province	C. topali Pia Oac Cao Bang	Yen So, Hanoi Hanoi	C. quadrilineatus Pogranichny and Khankaysky Primorsky Krai
Country Habitat	Vietnam Maize	Vietnam Grass	Russia Wheat
Reference n	Present paper 6♀♀	Andrássy (1970) ♀	Eroshenko (1968) 13♀♀
Body length a	317.7 ± 14.4 (306–345) 17.6 ± 1.4 (15.9–19.2)	310 17.0	310–387 13.8–18.7
b c	3.1 ± 0.2 (2.9–3.3) 14.4 ± 1.5 (12.7–17.0)	3.1 15.0	3.2–3.7 13.0–14.7
c' V	2.1 ± 0.3 (1.8–2.7) 64.3 ± 1.4 (62–65)	1.7 65	2.1* 61–68
Labial probolae	1.0 ± 0.1 (1.0-1.2)	1.4*	?
Lip region width Stoma length	6.0 ± 0.6 (5–6) 10.5 ± 0.6 (10–11)	7 13	??
Pharyngeal corpus Isthmus	56.5 ± 3.0 (51–59) 20.0 ± 1.6 (18–22)	62* 21*	??
Bulbus Pharynx length	15.2 ± 2.3 (14–20) 94.0 ± 5.0 (83–96)	14 97*	??
Nerve ring - anterior end	76.0 ± 7.4 (60–77)	67*	?
Excretory pore - anterior end Deirid - anterior end Neck length	68.0 ± 7.3 (57–72) 75.0 ± 6.0 (65–78) 104.5 ± 5.4 (93–107)	58* 71** 105*	?? 95**
Cardia Annuli	4.5 ± 0.8 (4–6) 1.0 ± 0.2 (1.0-1.4)	4* 1.3	??
Cuticle at midbody	0.8 ± 0.0 (0.8)	0.8	?
Body diameter at neck base Body diameter at midbody	18.5 ± 1.5 (16–20) 18.5 ± 1.9 (16–20)	20** 18**	? 22
Lateral field width Anterior ovary	4.0 ± 0.5 (3–4) 58.0 ± 16.9 (57–96)	3* 108*	??
Spermatheca Anterior uterus length	6.5 ± 0.6 (6–7) 19.5 ± 2.6 (18–24)	0? 47*	??
Postvulvar sac Vagina length	6.5 ± 1.3 (4–7) 5.0 ± 0.0 (5)	8* 4*	0?
Vulva - anterior end	201.8 ± 11.8 (189–224)	210**	192**
Rectum length Anal body diameter Tail length	15.0 ± 1.9 (14–19) 10.5 ± 1.5 (9–13) 23.0 ± 2.3 (18–24)	13** 13** 22	?? 25**
Phasmid - anus distance	8.5 ± 1.0 (7–9)	9**	?