Synonchiella rotundicauda, Leduc, 2013

Leduc, Daniel, 2013, Two new genera and five new species of Selachinematidae (Nematoda, Chromadorida) from the continental slope of New Zealand, European Journal of Taxonomy 63, pp. 1-32 : 4-9

Synonchiella rotundicauda sp. nov.

Figs 1-3 , Table 1

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Diagnosis

Synonchiella rotundicauda sp. nov. is characterised by cephalic setae 0.25 cbd long, mandibles each with two pairs of hooks and two wing-like projections laterally, multispiral amphideal fovea with 3.5 turns, eight cup-shaped pre-cloacal supplements, and short tail (2.2. abd) with rounded extremity.

Etymology

The species name is derived from the Latin rotundus (= round, circular) and cauda (= tail), referring to the unusual rounded shape of the tail.

Material examined

Holotype

NEW ZEALAND: ♂, NIWA 88354 , 17 Apr. 2007, NIWA cruise TAN0705, station 172, eastern Chatham Rise crest, 43.5162° S, 178.6167° W, 422 m, fine sand (53.5%), silt/clay (23.5%), very fine sand (18.9%).

Paratype

NEW ZEALAND: 1 ♀, NIWA 88355, 15 Nov. 2011, NIWA cruise TAN1116, station 107, northern flank of Chatham Rise, 42.8625° S, 177.9253° E, 467 m.

Description

Male

Body cylindrical, tapering slightly towards anterior extremity. Cuticle ~ 2.0 μm thick throughout body, thicker in tail region, 4 μm, with transverse rows of punctations, without lateral differentiation. Somatic setae short and sparse, in four sublateral rows. Head blunt, rounded, not set off. Six conical inner labial papillae, ~ 1.5 μm long; six longer outer labial setae, 4 μm long, and four cephalic setae, ~ 1 μm long, situated close to or slightly anteriorly to outer labial setae ( Fig. 1C ). Amphideal fovea cuticularised, multispiral, 3.5 turns. Anterior portion of buccal cavity short and narrow, with inconspicuous rhabdions at anterior extremity. Posterior buccal cavity with three equal mandibles, 15 μm long, with one mandible situated dorsally and two sub-ventrally; each mandible with two pairs of hooks at anterior extremity and two larger wing-like projections emerging laterally and pointing anteriorly; mandible also with small duct apparently connecting anterior extremity of marginal tubes and opening into buccal cavity near anterior end of mandible ( Fig. 1G ). Posterior buccal cavity surrounded by slightly swollen pharyngeal tissue, pharynx widening posteriorly, not forming true bulb. Several light refractive, golden-brown corpuscules present in pharyngeal region (also present in tail; Fig. 3A, B ). Nerve ring at 45% of pharynx length from anterior end. Secretory-excretory (S-E) system present, cellular body of ventral gland small, situated immediatly posterior to pharynx, pore situated ~ 0.5 cbd posterior to nerve ring.

Reproductive system diorchic with outsretched testes. Both anterior and posterior testes on right of intestine. Oval-shaped, nucleated sperm cells, ~ 6 × 7 μm. Spicules paired, strongly curved, 1.8 abd long, widest in middle portion and tapering distally; thin cuticular projection extending from proximal end over almost half of spicule length. Gubernaculum small, plate-like, without lateral pieces, parallel to distal end of spicules. Mid-ventral row of eight cup-shaped pre-cloacal supplements, ~ 4 μm wide and 4 μm deep, situated 6-8 μm apart; distance between supplements increasing slightly anteriorly. Pre-cloacal supplements thickly cuticularised with nerve entering anterior side of cup. No pre-or postcloacal setae or papillae observed. Tail short, with rounded posterior extremity, posterior half with few short setae and ducts, some of which are not connected to setae; terminal setae not observed. Three caudal glands and small spinneret present.

Female

Similar to males, but with smaller amphideal fovea, 2.5 turns. Reproductive system with posterior ovary reflexed, on right of intestine; anterior ovary poorly developed ( Fig. 2B ). Vulva located at mid-body. Vaginal glands present, pars proximalis vaginae surrounded by constrictor muscle.

Remarks

In contrast to Synonchiella rotundicauda sp. nov., all other Synonchiella species are characterised by relatively long, conico-cylindrical tails with a thin cylindrical portion. S. minor is characterised by a relatively short conical tail (2.9 abd), but can be distinguished from S. rotundicauda sp. nov. in having smaller amphid with 1.75 turns (vs. 2.5 turns in S. rotundicauda sp. nov.), longer spicules (200 vs. 51 μm), and more pre-cloacal supplements (42-46 vs. 8).

Figures

Fig. 1. Synonchiella rotundicauda sp. nov. A. Anterior body region of female. B. Male head. C. Surface view of male head. D. Surface view of female head. E. Male posterior body region. F. Female posterior body region. G. Mandibles, en face (left) and lateral (right) views. H. Spicule and gubernaculum. Arrow shows position of duct connecting anterior end of marginal tube and buccal cavity. Scale bar: A, E-F = 25 μm; B-D = 15 μm; G = 8 μm; H =13 μm.

Fig. 2. Synonchiella rotundicauda sp. nov. A. Entire male. B. Female reproductive system. Scale bar: A = 150 μm; B = 75 μm.

Fig. 3. Synonchiella rotundicauda sp. nov. Light micrographs. A. Anterior body region of male showing buccal cavity. B. Tail of male. C. Spicular apparatus. Scale bar = 25 μm.

Tables

Table 1. Morphometrics (μm) of Synonchiella rotundicauda sp. nov. and Pseudocheironchus ingluviosus gen. et sp. nov. — a = body length/ maximum body diameter; abd = anal body diameter; b = body length/pharynx length; c = body length/tail length; cbd = corresponding body diameter; L = body length; n = number of specimens; V = vulva distance from anterior end of body; %V = V/total body length.

Species	Synonchiella rotundicauda sp. nov.		Pseudocheironchus ingluviosus gen. et sp. nov.
	Male	Female	Males	Female
	Holotype	Paratype	Holotype Paratype	Paratypes
n	-	1	- 1	2
L	1411	1172	1034 992	940, 1209
a	43	32	25 25	25,27
b	8	7	12 9	9,12
c	23	20	24 22	21,26
Body diameter at level of cephalic setae	16	18	20 18	18, 21
Body diameter at level of amphids	26	30	23 24	25, 29
Length of cephalic setae	4	4-5	2 2	2, 3
Amphid height	14	7	9 12	7
Amphid width	14	10	17 16	10
Amphid width/cbd (%)	54	33	74 67	40
Amphid from anterior end	12	11	4 6	2, 5
Length of mandibles	15	14	18-20 19-21	22, 24
Nerve ring from anterior end	79	54	49 54	53, 54
Nerve ring cbd	33	36	39 35	38, 42
Excretory pore from anterior end	98	75	84 94	-
Pharynx length	180	163	88 105	99, 104
Pharynx diameter at base	24	24	25 24	29, 31
Pharynx cbd at base	36	38	40 37	39, 41
Max. body diam.	33	37	41 39	38, 44
Spicule length	51	-	51 48	-
Gubernaculum length	11	-	11 9	-
Anal body diam.	28	27	30 31	27, 32
Tail length	61	60	43 46	44, 46
Tail length/abd	2.2	2.2	1.4 1.5	1.4, 1.6
V	-	573	- -	438, 555
%V	-	49	- -	46,47
Vulval body diameter	-	37	- -	38, 43