A review of the genus Litinium Cobb, 1920 (Nematoda: Enoplida: Oxystominidae) with descriptions of four new species from two contrasting habitats
Author
Tchesunov, Alexei V.
Author
Thanh, Nguyen Vu
Author
Tu, Nguyen Dinh
text
Zootaxa
2014
2014-08-20
3872
1
57
74
journal article
http://dx.doi.org/10.11646/zootaxa.3872.1.5
55624991-3936-4a79-9ae0-39076cc7b826
1175-5326
287220
900D59EC-C85C-4DE0-A7AE-E1731FBA4183
Litinium abyssorum
Tchesunov, Nguyen Dinh Tu, Nguyen Vu Thanh
sp. n.
Fig.
4
,
Table
3
Material.
One
holotype
male and one allotype female.
The
specimens
are deposited in the Senckenberg Natural History Museum (
Frankfurt
am Main,
Germany
) with slide numbers
SMF
16981
(
holotype
male
)
and
SMF
16982
(
allotype
female
).
Locality.
South-east
Atlantic Ocean
,
Angola
Basin,
16
°17.0'S
,
005°27.0'E
, depth
5389 m
, silt—total carbon content
0.62
%, mud content
95.23
%, chlorophyll–a content
1.67
µ
g/g. DIVA–I expedition, st.
346
/
2
, Multicorer
3
;
27
July
2000
.
Description.
Body slim, cylindrical. Cuticle smooth and evenly thick (about
2
µ
m) over entire body.
Anterior end shaped as truncated cone; ratio of body diameter at the level of inner labial setae to that of the cephalic setae is
2 in
the male and
1.8 in
the female. There are two circles of six setae (inner labial setae and outer labial setae), consecutive but close to each other. The setae of both circles slender and cylindrical, nearly equal in length. Distance from the apex to the inner labial setae
2
µ
m in the male and
7
µ
m in the female. Circle of four cephalic setae situated posterior to the amphideal fovea, far posterior to the circle of outer labial setae; cephalic setae slender cylindrical and slightly shorter than setae of the two anterior circles. Amphideal fovea in male large, rounded in outer outline, with deep sinuous invagination on the surface at the anterior edge. Amphideal nerve emerges as broad funnel from beneath the posterior amphideal fovea. Amphideal fovea in female shaped in outline as an upside-down pear, with a small groove on its anterior edge; posterior smaller lobe of the fovea set off with a constriction. A number of minute somatic sensilla distributed sublaterally along the; each inserted in the middle of a short longitudinal ‘slit’ in the cuticle.
FIGURE 4.
Litinium abyssorum
sp. n.
A:
holotype male, entire;
B:
allotype female, entire;
C:
holotype male, anterior end;
D:
anterior end of the allotype female;
E:
anterior end of the allotype female, optical section;
F:
holotype male, posterior body;
G:
allotype female, tail. Arrows indicate somatic papillae in longitudinal slits in the cuticle (lo.sl.), gubernaculum (gub.), left vestigial spicule (l.sp.). Scale bars: A, B 300
µ
m; C–G 10
µ
m.
Mouth opening tiny. Somatic cuticle thickened slightly around the mouth opening. Buccal cavity not developed as such (internal lumen of the anterior pharynx not enlarged), but internal lining of the anterior pharynx thickened and cuticularised forming a narrow buccal capsule
13
µ
m long in the male and
15
µ
m long in the female. Pharynx gradually widening to the cardia; with clear internal cuticular lining; no muscular cross striation apparent in pharynx.
Nerve ring not seen. Ventral gland not visible.
Testes not discernible. A midventral seta
2
µ
m long
2
µ
m anterior to the cloacal opening. No precloacal midventral supplementary papillae. Right spicule short, weak, slightly curved, with slightly curved anterior handle. Left spicule reduced to a short straight rod-like structure with its pointed tip directed dorsally. Gubernaculum a short bar parallel to the spicule at its posterior part.
One posterior ovary antidromously reflexed and situated on the right of the intestine. Vulva depressed, surrounded by thickened cuticle.
Tail cylindrical, with rounded tip. There is a terminal pore, thin canal and coiling ducts of caudal glands with light transparent content. Caudal gland cell bodies with nuclei not visible. There is a minute lateroventral subterminal papilla on either side of the tail.
TABLE 3.
Morphometry of
Litinium abyssorum
sp. n.
Measurements in
µ
m.
| Character |
Specimens |
| Holotype male |
Allotype female |
| L |
710 |
897 |
| a |
50.7 |
69 |
| b |
4 |
4.31 |
| c |
15.7 |
13.3 |
| c’ |
3.61 |
5.76 |
| V, % |
- |
35.4 |
| diam.c.s. |
11 |
9 |
| diam.am. |
11 |
7.5 |
| diam.n.r. |
14 |
12 |
| diam.ca. |
15 |
12 |
| diam.midb. |
14 |
13 |
| diam.ani |
12 |
9 |
| i.l.s. |
3.5 |
3 |
| o.l.s. |
4 |
3 |
| c.s. |
2.5 |
2.5 |
| dis.c.s. |
23 |
14.5 |
| dis.am. |
7.5 |
6 |
| am.l. |
10 |
6 |
| am.w. |
8 |
5 |
| spic.arc (right) |
12.5 |
- |
| spic.arc (left) |
8 |
- |
Diagnosis.
Litinium
. Body length
710–897
µ
m;
a
50.7–69
;
c
13.3–15.7
;
c'
3.61–5.76
. Inner labial, outer labial, cephalic setae
2.5–4
µ
m in length. Amphideal fovea large, with deep anterior sinuous invagination of the external contour. Cephalic setae posterior to the amphideal fovea. One precloacal midventral supplementary seta just anterior to cloacal vent. Spicules unequal, the left spicule vestigial.
Differential diagnosis.
Litinium abyssorum
sp. n.
differs from all other
Litinium
species with known males by having unequal spicules. Further,
L. abyssorum
sp. n.
has a peculiar amphideal fovea with deep anterior invagination similar to those of
L. bananum
,
L. volutum
,
L. obtusilobus
and
L. profundorum
.
Litinium abyssorum
differs from
L. bananum
by smaller body length (
710–897
µ
m
vs
2140–3225
µ
m, shorter anterior setae (
2.5–4
µ
m
vs
10–14
µ
m), presence
vs
apparent absence of precloacal midventral seta; from
L. volutum
by simpler shape of the amphideal fovea without curls, one
vs
four preanal papillae in male and longer tail (
c
'
5.76
vs
1.5
, in females), from
L. profundorum
by longer tail (
c
15.7
vs
40.6
and
c'
3.6
vs
1.2
) and two
vs
one precloacal midventral setae, from
L. obtusilobus
by short cephalic setae (
2.5
µ
m
vs
5
µ
m) and relatively longer tail (
c'
5.8
vs
1.5
).
Etymology.
Species name is derived from Hellenic "abyssus" (abyss, chasm).