Trissonchulus latispiculum, Chen, Yu Zhen & Guo, Yu Qing, 2015

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 : 161-162

Trissonchulus latispiculum sp. nov.

( Figure 7 , Figure 8 , Table 3 )

Type material. Five males and two females were collected from Station QZLY H2 and QZLY H 4 in July 2012.

Holotype, ♂1 on slide number QZLY 20120713 H204. Paratypes: ♂2 and ♀1 on slide number QZLY 20120713 H207, ♂3 on slide number QZLY 20120713 H403, ♂4 and ♀2 on slide number QZLY 20120713 H204, ♂5 on slide number QZLY 20120713 H206.

Type locality and habitat. All specimens were collected from a mangrove ( Aegiceras corniculatum ) forest in the Luoyang River estuary in Quanzhou City. Station QZLY: 24.94°N, 118.67°E. Characteristics of surface sediments: total nitrogen (mg·g -1): 1.31; total phosphorus (mg·g -1): 0.40; organic carbon (%):1.72; sulfide (10-6): 16.89.

Etymology. The name refers to the broad spicules.

Measurements ( Table 3 )

Description. Male. Body cylindrical. Cuticle smooth without transverse or longitudinal striations. Head conical, continuous with body contour, with an inner circle of six small labial papillae. Six smaller outer labial papillae and four larger papilliform cephalic sensilla arranged in a crown. Amphids pouch-shaped, about 0.31–0.43 cbd and situated just posterior to the lateral outer labial papillae. Buccal cavity in the shape of a sclerotized tube which Inglis (1961) called a “pharynx rod”, and with a vestibular part, length 54–57 µm and 10–12 µm respectively. Three solid curved claw-like teeth embedded on the anterior edge of the sclerotized tube of buccal cavity, with the two subventral teeth almost equal in size and larger than the dorsal one. The inner wall of the vestibular part of buccal cavity lined with many minute denticles. Pharynx 0.13–0.16 times body length, gradually enlarging posteriorly, corresponding body diameter 75–95 µm at its posterior extremity. Сardia large, nearly heartshaped, surrounded by intestinal tissue. Nerve ring not very distinct, encircling pharynx at about 35–44% of its length. Excretory pore opening at the labial region, about equal distance to inner labial papillae and to cephalic sensilla. Ventral gland small, situated at 55–60% of pharynx length. Tail short, stout and blunt, armed with several papillae which are associated with more or less marked elevations of the cuticle. Spinneret opening slightly ventrally.

Reproductive system diorchic with two opposed testes, the anterior one longer than the posterior one; anterior testis situated to left and posterior testis mainly to right of intestine. Spicules paired, broad and alate, with prominent central septum and slight proximal cephalation. The median ridge of spicule slightly swollen to the lateral side. Gubernaculum relatively short and slightly thinner in proximal part, distally thick and well developed.

Female. Similar to male in general characteristics, except tail more round and slightly longer than male (c’ 1.32–1.42 vs. 1.23–1.31), the total length of buccal cavity in female slightly longer than in male (70–81 µm in female vs. 64–68 µm in male).

Reproductive system didelphic, opposed and reflexed, located at right side of intestine. Vulva at about 49.0% of body length. Oviduct twisted, ovaries asymmetrical.

Diagnosis and discussion. The genus Trissonchulus was erected by Cobb in 1920 with the type species T. oceanus . The taxonomy of this genus is still uncertain: the generic diagnosis and composition have been changed many times ( Schuurmans Stekhoven 1943, Wieser 1953, Chitwood 1960, Yeates 1967, Gerlach & Riemann 1974). However, the genus Trissonchulus in general can be distinguished from other genera of Ironidae by the papilliform or very short setiform head sensilla, the absence of posterior pharyngeal bulb and the relatively short tails, etc.

( Platt & Warwick 1983; Keppner & Tarjan 1989). There are 15 species in this genus at present; most of them were transferred from Dolicholaimus De Man, 1888 or Syringolaimus De Man, 1888 . ( Gerlach & Riemann 1974, Orselli & Vinciguerra 1997, Gagarin et al 2012; Electronic database: http://nemys.ugent.be; http:// www.marinespecies.org/index.php). However, T. nudus Schuurmans Stekhoven, 1943 was described from a single female; Gerlach & Riemann (1974) regarded it as a synonym of T. oceanus Cobb, 1920 ; T. reversus Chitwood, 1951 and T. acutus Gerlach, 1953 were described based on juvenile and female specimens respectively. Therefore, there are 14 species including 12 valid species and 2 species inquirenda in this genus ( Schuurmans Stekhoven 1943, Chitwood 1951, Gerlach 1953; Gerlach & Riemann 1974; Platonova & Mokievsky 1994,electronic database: http://www.marinespecies.org/index.php, http://nemys.ugent.be;). A pictorial key to 12 valid species as well as the newly described species of the genus Trissonchulus is given in Figure 9 , differentiating characters of all known male Trissonchulus species are given in Table 4 ( Bresslau & Schuurmans Stekhoven 1940, Wieser 1953, Gerlach 1967, Wieser 1959, Chitwood 1960, Inglis 1961, Yeates 1967, Orselli & Vinciguerra 1997, Gagarin et al. 2012).

Trissonchulus latispiculum sp. nov. is characterized by its continuous head (not set off from rest of body), short and blunt tail, buccal cavity with minute denticles, spinneret opening slightly ventrally, spicule broad and alate with proximal end with head, female reproductive system didelphic, etc. It most closely resembles T. latus ( Wieser, 1953) Inglis,1961 . However, in comparison with the original description of T. latus by Wieser (1953), the new species can be easily distinguished by its more slender body (a 36.4–54.2 vs. 22.2), shorter tail (c 45.3–61.4 vs. 44.3; c’ 1.2–1.3 vs. 0.9), slightly ventral spinneret opening (opening at the apex in T. latus ) and differently shaped spicule ( Wieser 1953; Platonova & Mokievsky 1994).

Figures

FIGURE 7. Trissonchulus latispiculum sp. nov. A: lateral view of male anterior part; B: lateral view of male posterior part; C: lateral view of female posterior part; D: lateral view of female anterior part; E: lateral view of male head end; F: lateral view of male copulatory apparatus G: lateral view of female reproductive system. Scale bar: 100 Μm.

FIGURE 8. Trissonchulus latispiculum sp. nov. A: lateral view of male head end, showing buccal cavity and teeth; B: lateral view of male head end, showing cephalic sensilla; C: lateral view of female head end, showing amphid; D: lateral view of female body part, showing reproductive system; E: lateral view of male tail region, showing copulatory apparatus; F: lateral view of female tail region. Scale bar: A, E, F = 25 Μm; B, C = 10 Μm; D = 50 Μm.

FIGURE 9. Pictorial key for valid species of genus Trissonchulus.

Tables

TABLE 3. Individual measurements of Trissonchulus latispiculum sp. nov. (in µm).

Characters	Holotype	Paratypes
	♂1	♂2 ♂3	♂4	♂5	♀1	♀2
Body length	3734	3643 3560	4123	4120	3352	4545
Head diameter	25	26 25	27	27	28	27
Total length of Buccal cavity	66	68 68	64	68	81	70
Amphid from the anterior end	10	13 14	12	14	15	14
Amphid diameter	12	12 11	10	12	10	10
Amphid cbd	28	28 30	30	30	32	30
Nerve ring from the anterior end	191	215 246	-	252	191	239
Nerve ring cbd	63	69 69	-	65	82	72
Pharynx length	551	576 571	544	570	465	572
Pharynx cbd	75	94 79	95	75	91	95
Maximum body diameter	77	95 80	96	76	92	95
abd	53	54 51	57	54	56	52
Tail length	65	65 67	74	69	64	74
c’	1.2	1.2 1.3	1.3	1.3	1.3	1.4
Spicule length as chord	65	69 71	66	64	-	-
Spicule length as arc	77	84 77	76	75	-	-
Length of gubernaculum	30	30 24	25	25	-	-
V’	-	- -	-	-	1631	2232
vbd	-	- -	-	-	73	84
V?%?	-	- -	-	-	48.7%	49.1%
a	48.5	38.3 44.5	42.9	54.2	36.4	47.8
b	6.8	6.3 6.2	7.6	7.2	7.2	7.9
c	57.4	56.0 53.1	55.7	59.7	45.3	61.4