Synonchium caudatubatum, Shi, 2018

Shi, Benze & Xu, Kuidong, 2018, Two new rapacious nematodes from intertidal sediments, Gammanema magnum sp. nov. and Synonchium caudatubatum sp. nov. (Nematoda, Selachinematidae), European Journal of Taxonomy 405, pp. 1-17 : 9-10

Synonchium caudatubatum sp. nov.

urn:lsid:zoobank.org:act:CDAACB82-D03D-4808-9B13-6B1AADFC9CF0

Figs 5–7 ; Tables 2–3

Diagnosis

Body cylindrical, length 2270–2760 μm. Labial and cephalic sensilla papillate. Anterior buccal cavity reduced, surrounded by 12 rhabdia, posterior buccal cavity with three mandibles each composed of one large tooth flanked by three smaller teeth on both sides. Amphideal fovea flattened multispiral, in about three turns. Pharynx largely cylindrical with slight anterior swelling but not forming a bulb. Two opposed testes, sperm globular to oval. Two spicules sclerotized and almost straight, 55–60 μm long. Two reflexed ovaries. Three caudal glands with spinneret. Tail bluntly rounded, with a protuberant caudal duct.

Etymology

The specific epithet is a composite of the Latin noun ‘ cauda ’ (tail) and the Latin adjective ‘ tubatus ’ (with tube), referring to the presence of a protuberant caudal duct, a main feature of the species.

Material examined

Holotype EAST CHINA SEA: ♂, Nanji Islands, Dasha’ao Beach , 27°27.76′ N, 121°3.48′ E, May 2014, intertidal sandy sediment, temperature 22°C, salinity at 28 psu during sampling, median particle diameter of sediment about 612 μm (coarse sand), sediment organic matter content about 2.5%, Benze Shi and Kuidong Xu leg. ( MBMCAS NJ-20140513-105 ) .

Paratypes

EAST CHINA SEA: 4 ♂♂, 5 ♀♀, same collecting data as for holotype ( MBMCAS NJ-20140513-9 , MBMCAS NJ-20140513-30 , MBMCAS NJ-20140513-73 , MBMCAS NJ-20140513-83 , MBMCAS NJ-20140513-84 , MBMCAS NJ-20140513-105).

Description

MEASUREMENTS. See Table 2.

BODY. Cylindrical. Anterior end of head almost truncate. Labial region with 12 lobes and six pairs of thin, membrane-like cuticle extensions ( Figs 5D–E , 6A ). Six inner labial papillae minute and conical situated on the lips, six outer labial papillae and four cephalic papillae large and conical. Cuticle thick and distinctly annulated, with lateral pores; each annule with a transverse row of punctations, without lateral differentiation. Amphideal fovea multispiral in about three turns, transverse oval-shaped ( Figs 5D , 6B ). Buccal cavity in two compartments: anterior one with 12 cuticularized rhabdia; posterior one surrounded by pharyngeal tissue, with three mandibles each bearing a large tooth flanked by three smaller teeth to each side ( Fig. 5E ). Pharynx cylindrical, with anterior end swollen. Nerve ring surrounding pharynx near its middle portion. Cardia flattened. Intestine cells large, filled with numerous small granules. Intestine lumen of irregular and variable appearance, containing remnants such as spicules and mandibles of prey nematodes ( Fig. 7C ). Three caudal glands with spinneret. Tail bluntly rounded, with a protuberant caudal duct ( Fig. 7C ).

Male

Two opposed testes short and broad, with anterior one slightly larger than posterior one, situated ventrally left to the intestine. Sperm cells globular to oval. Spicules sclerotized, almost straight, with proximal end weakly cephalated, distal end pointed and slightly bent ventrally. Gubernaculum and precloacal supplement absent.

Female

Similar to male except for reproductive system and sexual features. Two reflexed ovaries. Vulva a transverse slit in ventral view, located at posterior half of body (about 60%). Vagina short. Uterus broad.

Remarks

Synonchium Cobb, 1920 is characterized by the posterior buccal cavity equipped with three mandibles each composed of a large tooth flanked by several teeth and transverse oval-shaped multispiral amphideal fovea. The genus now contains nine valid species ( Heyns & Swart 1995; Vinciguerra & Orselli 1997; Kamran et al. 2009). Synonchium caudatubatum sp. nov. is unique in the genus by having a protuberant caudal duct in the tail end. The new species also differs from congeners by its mandibles, each with seven teeth, while all other known members have either three or five teeth ( Table 3). Synonchium caudatubatum sp. nov. lacks a gubernaculum and a precloacal supplement; both features occur in congeners except S. depressum Gerlach, 1954 , a species with a conical tail.

Figures

Fig. 5. Synonchium caudatubatum sp. nov., holotype, ♂ (A, C–F) and a paratype, ♀ (B). A. Overview, showing the slightly slender body shape, the broad anterior buccal cavity and the narrow posterior buccalcavity with threemandibles, thecylindrical pharynx with anterior end swelling, the two opposed testes with oval sperm cells, the almost straight spicules without gubernaculum, the caudal glands with spinneret, and the bluntly rounded tail with a protuberant caudal duct. B. Overview, showing same structures as male holotype except the two reflexed ovaries. C. Eachmandible has a large tooth flanked by three small teeth to each side. D–E. Head, showing the papillate sensilla, transverse oval amphideal fovea, transverse rows of punctuations, lateral cuticle pores, the broad anterior buccal cavity and the narrowposteriorbuccalcavitywiththreemandibles.F.Tail,showingthealmoststraightspiculeswithout gubernaculum, the three caudal glands with spinneret, and the bluntly rounded tail with protuberant caudal duct. Scale bars:A–B, D–F = 50 μm, C = 50 μm.

Fig. 6. Synonchium caudatubatum sp. nov. holotype, ♂ (A–C) and a paratype, ♂ (D). A–B. Head, showing the papillate sensilla, transverse ovalamphideal fovea, transverse rows of punctuations, lateral cuticle pores, the broad anterior buccal cavity and narrow posterior buccal cavity with three mandibles each with seven teeth, and the swelling anterior end of pharynx. C. Tail, showing the almost straight spiculeswithoutgubernaculum,andthebluntlyroundedtailwithaprotuberantcaudalduct.D.Overview, showing the slightly slender body. Scale bars:A–C = 30 µm, D = 100 µm.

Fig. 7. Synonchium caudatubatum sp. nov., paratypes, ♀♀. A–B. Head, showing the same structures as male holotype. C. Spicules (arrow) of prey nematodes left in the intestine. D. Tail, showing the caudal glandswith spinneretandthe bluntlyrounded tail witha protuberantcaudalduct.E. Overview, showing the slightly slender body shape and two opposed testes. Scale bars:A–D = 50 µm, E = 100 µm.