Trissonchulus oceanus Cobb 1920

Chen, Yu Zhen & Guo, Yu Qing, 2015, Three new and two known free-living marine nematode species of the family Ironidae from the East China Sea, Zootaxa 4018 (2), pp. 151-175 : 169-170

Trissonchulus oceanus Cobb 1920

( Figure 12 , Figure 13 , Table 6 )

Material. Five males and two females were collected from Station ZZDS H1, H2 and H 3 in May 2013. ♂1 on slide number ZZDS 20130518 H3U104, ♂2 on slide number ZZDS 20130518 H2D116, ♂3 on slide number ZZDS 20130518 H1U101, ♂4 on slide number ZZDS 20130518 H2U104, ♂5 on slide number ZZDS 20130518 H1D103, ♀1 on slide number ZZDS 20130518 H3U103, ♀2 on slide number ZZDS 20130518 H2D116.

Material locality and habitat. All specimens were collected from intertidal sandy sediment at Dongshan Island, Zhangzhou City, East China Sea. Station ZZDS: 117.4836°E, 23.7081°N. Silt+clay: 3.27%.

Measurements ( Table 6 )

Description. Male. Body cylindrical. Cuticle smooth and unornamented. Head region set off by a suture line, bearing an inner circle of six minute labial papillae near the anterior end of the lips. Ten cephalic papillae small and rounded, the submedian pairs scarcely distinguishable as double. Amphids pouch-shaped, about 0.38–0.46 cbd, adjacent to the suture line of the head. Buccal cavity consists of a cup-shaped anterior section and a strongly cuticularized posterior tube, length 7–10 µm and 37–41 µm respectively. Three solid teeth of almost equal size embedded on the border of the cup-shaped anterior section and cuticularized posterior tube of buccal cavity. The inner wall of cup-shaped anterior section of buccal cavity covered with numerous rows of minute denticles. Pharynx 0.12–0.14 times body length, slightly swelling in stomatal region and gradually enlarging at posterior end but not forming a bulb, corresponding body diameter 40–56 µm at posterior extremity. Сardia well developed, surrounded by intestinal tissue. Nerve ring encircling pharynx at about 42–48% of its length. Excretory pore opening ventrally 30–40 µm from anterior end, ventral gland not observed. Tail short, stout and slightly curved ventrally, with three pairs of scattered papillae, which are associated with more or less marked elevations of the cuticle. Spinneret opening ventrally. Anterior lip of the cloaca with a swelling pierced by a pore, and a similar swelling on the tail behind the spinneret. Male caudal region armed with 2–4 pairs of precloacal and 1–2 pairs of postcloacal, but pre-spinneret ventral submedian papillae. Both precloacal and postcloacal ventral submedian papillae appear to be tube-like under the cuticle.

Testes paired and opposed. Spicules paired and broad, slightly curved ventrally, with cephalated proximal end and central septum. Conspicuous copulatory muscles are present. Gubernaculum relatively short and well developed in its distal part.

Female. Similar to male in general characteristics, except tail more round, neither precloacal nor postcloacal ventro-submedian papillae present, the swellings pierced by a pore on the anterior lip of the anus and behind the spinneret are both absent, but with three pairs of papillae which are associated with more or less marked elevations of the cuticle present, as in male.

Reproductive system with anterior oviduct present but anterior ovary strongly reduced and apparently nonfunctional, posterior oviduct and ovary well developed and reflexed. Vulva strongly cuticularized, situated at about 47%–49% of body length.

Diagnosis and discussion. Trissonchulus oceanus was described by Cobb in 1920 and has been described several times. It is characterized by its buccal cavity with minute denticles; tail short, wide and bluntly rounded; spicules stumpy and strongly blunt; male with caudal papillae and supplements; female reproductive system with anterior oviduct present but anterior ovary strongly reduced and posterior oviduct and ovary well developed. ( Cobb 1920, Platonova & Mokievsky 1994). Our specimens conform to the original description by Cobb in 1920, but differ from it in smaller body size (2.3–2.7 mm vs. more than 3.6 mm) and the number of precloacal and postcloacal ventro-submedian papillae (2–4 pairs of precloacal and 1–2 pairs of postcloacal vs. 3 precloacal and 4 postcloacal on each side) ( Cobb 1920). Compared with the redescription of the holotype from the Red Sea by Gerlach in 1967, our specimens differ in smaller body size (2273–2673 µm vs. 3247–3335 µm), longer pharynx (b 7.3–8.4 vs. 8.6–9), posterior situation of vulva (V 47 %–49% vs. 41%); fewer precloacal supplements (2–3 vs. 9) ( Gerlach 1967).

Figures

FIGURE 12. Trissonchulus oceanus Cobb 1920 A: lateral view of female anterior part; B: lateral view of female posterior part; C: lateral view of male tail region and copulatory apparatus; D: lateral view of male anterior part; E: lateral view of male head; F: lateral view of female reproductive system. Scale bar: 50 Μm.

FIGURE 13. Trissonchulus oceanus Cobb 1920 A: lateral view of male head end, showing buccal cavity and teeth; B: lateral view of male head end, showing cephalic sensilla and amphid; C: lateral view of female head end, showing amphid; D: lateral view of female body part, showing vulva; E: lateral view of male body part, showing spicule; F: lateral view of male tail region, showing gumbernaculum; G: lateral view of male tail region, showing caudal papillae; H: lateral view of male tail region; I: lateral view of female tail region. Scale bar: A ~ G = 10 Μm; H, I = 25 Μm.

Tables

TABLE 6. Individual measurements of Trissonchulus oceanus Cobb 1920 (in µm).

Characters	♂1	♂2	♂3	♂4	♂5	♀1	♀2
Body length	2673	2273	2640	2343	2587	2668	2492
Head diameter	25	23	22	24	24	24	25
Total length of Buccal cavity	47	47	46	48	47	49	47
Amphids from the anterior end	9	9	9	10	10	9	8
Amphid diameter	11	10	10	11	10	9	10
Excretory pore from the anterior end	30	30	36	30	40	35	31
Excretory pore cbd	34	34	30	32	35	33	35
Nerve ring from the anterior end	145	136	153	135	141	145	141
Nerve ring cbd	45	50	36	39	41	42	51
Pharynx length	319	286	324	321	325	329	317
Pharynx cbd	49	51	40	41	43	43	56
Maximum body diameter	51	55	42	42	48	54	59
abd	38	42	36	38	38	38	42
Tail length	55	53	57	53	59	49	53
c’	1.4	1.3	1.6	1.4	1.6	1.3	1.3
Spicule length as chord	41	44	39	41	42	-	-
Spicule length as arc	42	46	41	43	43	-	-
Length of gubernaculum	21	24	20	20	19	-	-
V’	-	-	-	-	-	1320	1183
vbd	-	-	-	-	-	48	54
V (%)	-	-	-	-	-	49	47.5
a	52.4	41.3	62.9	55.8	54.0	49.4	42.2
b	8.4	7.9	8.1	7.3	8.0	8.1	7.9
c	48.6	42.9	46.3	44.2	43.8	54.4	47.0