Three new species of the free-living marine nematode Metoncholaimus Filipjev 1918 (Enoplida, Oncholaimidae) from Argentinean coasts
Author
Russo, Virginia Lo
Author
Pastor De Ward, Catalina T.
text
Zootaxa
2019
2019-10-21
4688
1
86
100
journal article
25184
10.11646/zootaxa.4688.1.4
467d7661-2612-4093-9bde-1ccb1f653152
1175-5326
3514856
99EAED44-1050-4571-B02C-5B1BEE9B3B56
Metoncholaimus perdisus
sp. n.
(
Figure 3
;
Table 2
)
Measurements.
See
Table 2
.
Description. Males:
Body cylindrical, slender, tapering towards the posterior end. Cuticle smooth. Lip region with six inner labial sensilla (R1) papilliform, 6 + 4 outer labial sensilla (R2) + cephalic sensilla (R3),
7–10 µm
and
6–7 µm
long respectively, arranged in a single circle just in the limit of endocupola. Buccal cavity with sclerotized walls, narrower in posterior part. Two subventral teeth and one dorsal tooth. Left subventral tooth is the longest (
21 µm
) and others are similar in length (ca
15 µm
). Amphids opening oval (about 1/3 of the corresponding diameter) and fovea bowl-shaped. Some short cervical setae (
3–5 µm
) distributed anterior to nerve ring. Then, few longer somatic setae (ca
10 µm
) scattered throughout body. Excretory pore faintly visible located in anterior part of pharynx at about two buccal cavity lengths from anterior end. Nerve ring lying at about 45% of pharynx length. Pharynx cylindrical. Cardia conoid, large. Diorchic reproductive system, with opposed and outstretched testes, in right position relative to intestine. Spicules paired, short, slender, not cephalate, ca 2 anal body diameter long. Gubernaculum small, delicate and tubular, 25% of the spicules length. Two pairs of precloacal setae and three pairs of postcloacal setae are present. Two tiny pre- and one postcloacal pore can be observed at cloaca. Tail ca 3 anal body diameters in length, conico-cylindrical in shape. Two pairs of short ventral and two dorsal (
6 µm
) caudal setae. Spinneret well developed with two short and two longer terminal seta. Dorsolateral and ventrolateral metanemes not observed.
Females:
Similar to males in general body shape, anterior sensilla, amphideal fovea and cuticle. One anterior ovary, reflexed, on right side of intestine. Vulva slightly sclerotized, slit-like. Post-uterine sac present. Demanian system present (
Figure 5
). Uterus connects through ductus uterinus with uvette (located ca
170 µm
after vulva). Osmosium is located at ca
440 µm
from vulva. Ductus entericus was not observed. The main tube starts at osmosium, ending at ca
170 µm
into two terminal pores. Tail conico-cylindrical, but with cylindrical portion longer.
Type
material.
All
the specimens are deposited in the CNP-NEM collection in the
Centro Nacional Patagónico
(
Chubut
,
Argentina
)
.
FIGURE 3.
Metoncholaimus perdisus
sp. n.
: (A) Head region (internal) of holotype male (CNP-NEM 16668); (B) Head region (external) of holotype male (CNP-NEM 16668); (C) Posterior end of paratype female (CNP-NEM 16827); (D) Head region (in- ternal) of paratype female (CNP-NEM 16827); (E) Head region (external) of paratype female (CNP-NEM 16827); (F) Posterior end of holotype male in ventral view (sketch); (G) Posterior end of holotype male (CNP-NEM 16668). Scale bars: 1= 20 µm.
Type locality and habitat.
Holotype
: adult male.
Registration
number CNP-NEM 16668; type locality:
Banco Perdices
(
San Antonio bay
); coordinates:
40°46ʹ52ʺ S
;
64°51ʹ05ʺ W
; low littoral, fine sand sediments. Collected by
V. Lo Russo
y
G. Villares
,
12 February 2009
.
Paratypes
: Four males and five females. Registration numbers CNP- NEM 16521/16727/16745/16798 (males) and CNP-NEM 16564/16711/16769/16827/19959 (females). Same data as
holotype
.
TABLE 2.
Measurements (μm) of
Metoncholaimus perdisus
sp. n.
including mean values (range).
| Holotype ♂ |
4 ♂ |
5 ♀ |
| L |
2620.0 |
2628 (2550–2720) |
2470 (2220–2680) |
| a |
68.9 |
72.3 (63.7–85) |
58.7 (49.3–70.8) |
| b |
6.6 |
6.6 (6.4–6.8) |
5.9 (4.9–6.5) |
| c |
35.4 |
34.8 (32.7–36) |
21.4 (17.8–23.1) |
| Cephalic sensilla (R3) |
6.0 |
6.4 (6–7) |
5.6 (5–6) |
| Outer labial sensilla (R2) |
7.0 |
8.6 (7–10) |
7.8 (7–8) |
| Buccal cavity diameter |
18.5 |
18.6 (14–24.5) |
15.8 (12.5–18) |
| Buccal cavity length |
30.0 |
30.6 (27–38) |
26 (23–28) |
| Lip region diameter |
28.0 |
24 (21–28) |
27.3 (20–37) |
| Amphid diameter |
9.0 |
8.94 (7–10) |
7.6 (6–9) |
| Width of amphideal fovea as percentage of corresponding body diameter (%) |
30.0 |
32 (23.3–42.2) |
28.7 (20–38.1) |
| Cervical setae length |
4.0 |
3.9 (3–5) |
4.2 (3.5–5) |
| Excretory pore from anterior end |
60.0 |
67.4 (60–76) |
73.2 (61–93) |
| Nerve ring from anterior end |
178.0 |
179.2 (170–188) |
169 (153–175) |
| Body diameter at nerve ring |
34.0 |
31.4 (28–36) |
36.4 (30–39) |
| Pharynx length |
400.0 |
397.6 (380–410) |
416 (380–450) |
| Body diameter at pharynx base level |
36.0 |
32.2 (28–38) |
38.1 (29.5–43) |
| Maximum body diameter |
38.0 |
36.6 (32–40) |
42.4 (37–46) |
| Anal/cloacal distance from anterior end |
2546.0 |
2552.4 (2472–2640) |
2354.2 (2095–2564) |
| Anal/cloacal body diameter |
28.0 |
26.2 (23–29) |
28 (26–30) |
| Spicule length |
51.0 |
50.4 (48–54) |
– |
| Spicule length as cloacal diameter |
1.8 |
1.9 (1.8–2.1) |
– |
| Gubernaculum length |
11.0 |
12.4 (11–13) |
– |
| Gubernaculum length as cloacal diameter |
0.1 |
0.07 (0.06–0.09) |
– |
| Vulva from anterior end |
– |
– |
1582 (1320–1730) |
| V (%) |
– |
– |
64 (58.1–67.6) |
| Tail length |
74.0 |
75.6 (71–80) |
115.8 (100–125) |
| c’ |
2.6 |
2.9 (2.6–3.4) |
4.1 (3.8–4.3) |
Etymology.
In reference to “Banco Perdices”, the name of the site where the sample was collected.
Differential diagnosis.
Metoncholaimus perdisus
sp. n.
is characterized by small size, short spicules, small gubernaculum, presence of long pre- and postcloacal setae and presence of pre- and postcloacal pores.
Metoncholaimus perdisus
sp. n.
belongs to the species of
Metoncholaimus
with short spicules (4 or less anal diameters in length) and presence of gubernaculum (
Table 4
).
Metoncholaimus perdisus
sp. n.
is thus related to
M. amplus
,
M. anthophorus
,
M. moles
,
M. murphyi
,
M. pelor
and
M. siddiqii
.
M. amplus
,
M. pelor
and
M. siddiqii
are bigger than the new species, have longer spicules, do not have somatic setae after the nerve ring (
vs
present in
M. perdisus
sp. n.
) and just one precloacal pore (
vs
two pre- and one postcloacal pores in
M. perdisus
sp. n.
) (
Table 4
).
M. amplus
has spicules with cuticular ridges in the distal extremity unlike the new species that has spicules with smooth end. The females of
M. amplus
,
M. pelor
and
M. siddiqii
have slit-like pores in the Demanian system.
M. perdisus
sp. n.
has rounded pores.
M. anthophorus
and
M. moles
have the excretory pore at the base of the buccal cavity
vs
two stomatal lengths from the anterior end in the new species. Also, they have many more cloacal setae (
Table 4
).
M. moles
has a curved spicule (
vs
straight in
M. perdisus
sp. n.
) and gubernaculum with apophysis (
vs
gubernaculum without apophysis).
M. murphyi
is similar to
M. perdisus
sp. n.
in general body size and number of cloacal setae (
Table 4
). The species can be differentiated by the presence of a bump in the males of
M. murphyi
, absent in the new species and in the length of the spicules. The Demanian system of females in
M. murphyi
has only one terminal pore
vs
two pores in
M. perdisus
sp. n.
(
Table 4
).