Epacanthion longicaudatum, Shi & Xu, 2016

Shi, Benze & Xu, Kuidong, 2016, Four new species of Epacanthion Wieser, 1953 (Nematoda: Thoracostomopsidae) in intertidal sediments of the Nanji Islands from the East China Sea, Zootaxa 4085 (4), pp. 557-574 : 561-564

Epacanthion longicaudatum sp. nov.

( Figs 4 , 5 ; Table 2)

Diagnosis. Body length 2–2.7 mm. Mandible about 8 mm long and 0.7–0.8 times maximum width. Three onchia of unequal size. Anterior pharyngeal bulb present. Ten groups of subcephalic setae in males, each composed of one long, one medium and one short seta. Roughly three circles of long cervical setae. A cervical circle of 16 bundles each composed of six distinctly short setae arranged in two longitudinal rows posterior to nerve ring in males. Spicules 0.9–1.2 anal body diameter, with small tubular gubernaculum. Precloacal supplement located at 3 anal body diameter anterior to the cloaca. Tail slenderly conical-cylindrical, about 7.5 anal body diameter. Three long subterminal setae.

Type material. Holotype: One male on slide NJ-20140513-1 . Paratypes: one male on slide NJ-20140513-92 and six females on slides NJ-20140513-92, -31, -93 and -115. All type slides have been deposited in the Marine Biological Museum of Chinese Academy of Sciences .

Type locality. Intertidal sandy sediment from Dasha’ao Beach of the Nanji Islands in the East China Sea.

Etymology. Composition of the Latin adjectives longus (long) and caudatus (caudate: having a tail), referring to the long tail of the species.

Measurement. See Table 2.

Description. Body cylindrical. Cuticle smooth and very thick, apparently with sub-surface annulations. Head slightly tapering, chisel-shaped. Cephalic capsule strongly sclerotized. Lips high, subsidiary lobes slit, without obvious striation. Cephalic organs circular. Anterior sensilla (6+10) in two circles: six inner labial setae, six outer labial setae and four short cephalic setae in the second row. Cephalic setae inserted at posterior part of head capsule. Three mandibles and three onchia. Mandibles strongly cuticularized and separated by a sheet of cuticle, with anterior points curved outwardly; about 8 mm long and about 0.67–0.83 times maximum width of mandibles. Three onchia unequal in size with two subventral onchia larger than the dorsal one. Pharyngeal glands opening into tips of onchia. Amphideal fovea indistinct. Pharynx very narrow and slightly muscular, narrowest at the level of nerve ring. Anterior pharyngeal bulb present. Cardia reduced. Three caudal glands, with cells positioned precaudally. Tail slenderly conical-cylindrical, length 210–236 mm and 6.7–7.9 abd. Several setae with no distinct pattern at the middle portion of tail, and about three long subterminal setae present. Terminal setae absent.

Males. Ten groups of subcephalic setae in a circle, each composed of one long, one medium and one short seta. Numerous long setae roughly arranged in three circles at pharyngeal region: the first one composed of about 40 setae, the middle and the third one each with about 20 setae. A cervical circle of 16 bundles each composed of six distinctly short setae in two longitudinal rows located posterior to nerve ring at the anterior third of pharynx ( Figs 4A, B , 5E, F ). Two testes opposed, located on the left of intestine. Spicules slightly curved, with distal end pointed, equal in length, 25–35 mm long and about 0.9–1.2 anal body diameter. Gubernaculum conical, with tip slightly curved downwards, about one fifth of spicule length. One tubular precloacal supplement about 86–92 µm distant from cloaca (about three times of anal body diameters).

Females. Females similar to males in body shape, but slightly larger in size. Only 12 subcephalic setae in a circle. Setae at pharyngeal region fewer than those in males. Three rough circles of long setae present, but without the fourth circle of bundles of short and dense setae. Vulva located at about 55% of the body. Ovaries paired, opposed reflexed, both on the left side of intestine. Vulva a transverse slit.

Figures

FIGURE 4. Epacanthion longicaudatum sp. nov. A – C: anterior portion of the male holotype, showing the mandibles and onchium, the narrow pharynx and the cervical circle of 16 bundles each composed of six distinctly short setae arranged in two longitudinal rows posterior to the nerve ring; D, E: posterior portion of the male holotype showing the spicules and gubernaculum and the long tail. Bars = 30 µm (A, D and E), 10 µm (C).

FIGURE 5. Epacanthion longicaudatum sp. nov. A, C: head and tail of the male holotype; B, D: head and tail of a female; E, F: cervical circle of 16 bundles each composed of six distinctly short setae arranged in two rows (arrows); G, H: precloacal supplement (arrow), spicules and gubernaculum of the male holotype. Bars = 30 µm (D, G), 10 µm (H).