Three new species of the genus Mononchus (Nematoda: Mononchida), and the “ real ” Mononchus truncatus Bastian, 1865
Author
Andrássy, István
text
Journal of Natural History
2011
2011-02-28
45
5 - 6
303
326
http://dx.doi.org/10.1080/00222933.2010.524947
journal article
10.1080/00222933.2010.524947
1464-5262
5204935
Mononchus oblongus
sp. nov.
(
Figures 4A–F
and
5A–F
)
Holotype
female: L =
1.72 mm
; a = 29; b = 3.7; c = 6.2; c’ = 9.0;
V
= 54
%.
Paratype
females (
n
= 5): L =
1.60–1.88 mm
; a = 25–28; b = 3.5–3.7; c = 6.0–7.1; c’ = 7.5–8.8;
V
= 52–54%.
General characters
Body medium long, on average
1.72 mm
, 39–42 µm wide at posterior end of buccal cavity, 60–65 µm wide at cardial region, 60–68 µm wide at mid-body region and 30–36 µm wide at posterior anal lip. Habitus almost straight upon fixation. Cuticle smooth, its thickness more or less uniform, 2 µm, but thicker on tail, 3.0–3.5 µm. Labial region practically not offset, 22–23 µm wide at level of lateral lips. Lips amalgamated. Body at proximal end of pharynx 2.7–2.9 times as wide as labial region. Oral field slightly protruded, about 3 µm high. Amphids small, caliciform, their aperture located somewhat posterior to beginning of buccal capsule.
Distance between the oral field and beginning of buccal capsule 7–9 µm. Buccal capsule oblong, 48–51 µm long, 18–19 µm wide at anterior third and 17–18 µm wide at posterior third, 2.6–2.8
/
2.8–3.1 times as long as wide at anterior or posterior third, respectively. It is 2.1–2.3 times as long as labial diameter, and occupies 10.0–10.8% of entire length of neck region (from oral field to cardia). Buccal walls about 1.5 µm thick, but 2.5 µm thick just posterior to dorsal tooth, at its thickest point. Dorsal tooth 5–6 µm long from base to apex, its apex situated 10.0–11.5 µm from beginning of buccal capsule or at 21–23% of buccal length. Distance between tooth apex and opposite stomatal wall 11–12 µm. Subventral transversal ridges very thin, lying at level of tooth apex. Pharynx 450–504 µm long, cylindrical and strongly muscular. Pharyngeal collar surrounding the posterior 20–25% of stoma. Nerve ring situated at 24–27% of pharynx. Cardia simple. Rectum nearly one anal body width long.
Female
Reproductive system amphidelphic with reflexed ovaries. Genital branches short, each 2.2–2.7 body widths long or occupying 7.6–9.4% of body length. Uterus separated from the oviduct by a sphincter. Vulva a transverse slit with sclerotized, drop-shaped inner lips. Vagina 18–21 µm long, nearly as long as one-third body diameter. Mature eggs not observed. Distance between posterior end of pharynx and vulva almost as long as pharynx. Vulva–anus distance equal to 1.8–2.4 tail lengths. Tail 264– 276 µm (on average 270 µm) long, occupying 14.0–16.8% of entire length of body; first quickly then slowly tapered, in posterior third cylindrical and 4–5 µm thick. Caudal glands rather small. Tip of tail rounded with a terminal spinneret and two ventral
/
subventral papillae, which are setiform, 2–3 µm long, longer than in other species of the genus.
Figure 4.
Mononchus oblongus
sp. nov.
(A) Anterior end; (B) cardial region; (C) vulval region; (D, E) female posterior end; (F) tail tip. Scale bars 20 µm.
Figure 5.
Mononchus oblongus
sp. nov.
(A–C) Anterior end; (D) cardial region; (E) vulval region; (F–H) female posterior region; (I) tail end with setiform papillae.
Male
Not found.
Diagnosis and relationships
The most striking morphological features of this new species are the shape and length of the buccal cavity, which is more elongate than in other congeners of similar body size, and the seta-like subterminal papillae on the tail. This new species is further characterized by an average body length of
1.72 mm
, a fairly robust shape, relatively anterior position of the dorsal tooth apex at 21–23%, short gonads, sclerotized vulva, and by the medium-size, on average 8.2 anal body widths long tail.
Cobb (1917)
described a new species under the name
Mononchus megalaimus
Cobb, 1917
from
Wisconsin
,
USA
, which was later synonymized with
M. truncatus
.
Although Cobb gave a brief description, he illustrated the buccal region well. The buccal capsule is elongated, oblong, about 43 µm long, 1.8–1.9 times as long as the lip region width.
Mononchus oblongus
differs from it in having a longer buccal cavity (48–51 vs 43 µm, 2.1–2.3 vs 1.8–1.9 lip region width), longer tail (264–276 vs 210 µm), and in having long, setose caudal papillae (vs “very small”).
Nakazawa (1999)
studied several specimens of
M. truncatus
from paddy fields in
Japan
. He illustrated the buccal region of one population as very similar to that of the present new species. Unfortunately, he gave no description of this form. All that is known is that the buccal capsule is about 50 µm long, and the tooth apex is located at 24%.
By virtue of the characteristic shape of the buccal cavity,
M. oblongus
sp. nov.
comes close to
M. himalayensis
Rawat and Ahmad, 2000
. It can be differentiated from the latter by the more elongate buccal cavity (2.1–2.3 vs 1.6–1.8 labial widths long), the position of the dorsal tooth apex (21–23 vs 25–31%), the lack of a prevulval papilla, the conspicuously thinner tail (4–5 vs 10 µm thick at its posterior cylindrical section), as well as by the setose subterminal caudal papillae.
As for the terminal caudal papillae, the observation of
Zullini et al. (2002)
should still be mentioned. They found in
M. truncatus
Bastian, 1865
from
Costa Rica
that “The tail bears two small projections more similar to setae than to papillae.” Because of the lack of illustrations it cannot be decided whether those specimens belonged to
M. truncatus
or to another (perhaps new) species. Yet it seems certain that the Central American nematodes were not conspecific with
M. oblongus
sp. nov.
because of their shorter buccal cavity (39–43 vs 48–51 µm; 1.6–1.7 vs 2.1–2.3 labial diameters long), more posteriorly located tooth apex (24–30 vs 21–23%) and shorter tail (185–234 vs 264–276 µm).
Type specimens
Holotype
female on slide no. 14782.
Paratypes
:
five females
and
two juveniles
; deposited in the nematode collection of the
Department of Systematic Zoology
and
Ecology
of the
Eötvös Loránd University
,
Budapest
.
Type habitat and locality
Liver mosses from the soil near the village Ossès (Basque: Ortzaize) in the Pyrénées- Atlantiques département, southwestern
France
, near the French–Spanish border, about
200 m
above sea level. Collected in
June 1997
by K. Dózsa-Farkas (Budapest).
Etymology
The species epithet
oblongus
(Latin)
means elongate or oblong referring to the shape of the buccal cavity, which is more elongated than usual.