Paracomesoma longissimum, Huang & Shi & Wang & Xu, 2021

Huang, Mian, Shi, Benze, Wang, Chunguang & Xu, Kuidong, 2021, Two new species of nematodes from shallow and deep-water sediments in the South China Sea, Zootaxa 5016 (4), pp. 490-502 : 496-499

Paracomesoma longissimum sp. nov.

( Figs 4–5 ; Table 2)

Diagnosis. Body length 2514–2750 μm, a=94.8–96.7; cuticle with fine transverse rows of punctuations, without lat- eral differentiation; buccal cavity elongate conical, about 13 μm long, with three small teeth; two lateral outer labial setiform sensilla about 1.5 times as long as the other four outer labial sensilla; cephalic setiform sensilla 20–32 μm long; multispiral amphideal fovea with 2.5 turns; spicules 350–360 μm long, about 16 times as long as cloacal body diameter; gubernaculum plate-like, without apophyses; and 25–28 papilliform precloacal supplements.

Type material. Holotype: one male on slide MBM286826 , Paratype: one male on slide MBM286827 .

Type locality and habitat. Continental slope in the northeastern South China Sea (21°04′09′′N, 115°31′44′′E), where the water depth was about 273 m and the sediment was muddy at station W7 .

Etymology. The Latin adjective longissimus (very long) refers to a distinct feature of the species, viz. the very long spicules.

Description of male holotype. Body slender, about 2750 μm long. Cuticle with transverse rows of fine punc- tuations, without lateral differentiation ( Fig. 3C ). Head slightly set off by a contraction at the level of cephalic setae, and the head diameter (the body width at the level of cephalic setae) is 13 μm. Buccal cavity 13 μm long, conical. Head sensilla arranged following 6+6+4 pattern. Inner labial sensilla papilliform; six outer labial setae unequal in length, lateral outer labial sensilla about 8 μm long, 1.5 times as long as the other four outer labial sensilla ( Fig. 3A, C ). Cephalic setiform sensilla 32 μm long, located at 0.5 of the head diameter from the anterior end. Scattered somatic setae present in pharyngeal region, about 10 μm long. Multispiral amphideal fovea with 2.5 turns, located just posterior to cephalic setae ( Figs 3A, C , 4A ). Pharynx cylindrical, 226 μm long, posterior portion not enlarged. Cardia well developed. Nerve ring about 130 μm from anterior body extremity (58% of the pharynx length). Secre- tory-excretory system consisting of an unicellular gland located at the level of anterior part of intestine; secretoryexcretory duct with distinct ampulla and opening just posterior to nerve ring ( Fig. 3A ).

Male reproductive system diorchic. Two testes opposed and outstretched, anterior testis on the left of intestine and posterior testis on the right. Spermatozoa irregularly oviform. Spicules very long and slender, 350–360 μm long, about 15.7 times as long as cloacal body diameter, parallel to body axis with slightly swollen proximal end and pointed distal end, gubernaculum plate-like, without apophysis, about 16 μm long ( Figs 3B, D , 4C, D ). One short precloacal seta located just in front of cloaca. 25–28 papilliform precloacal supplements. Tail composed of a slightly conical anterior half and a cylindrical posterior half slightly swollen posteriorly, about 168 μm long and equal to 7.3 body diameters at the level of cloaca, with three terminal setae about 22 μm long. Three caudal glands and spinneret.

Male paratype showing similar morphology. Female not found .

Figures

FIGURE 3. Gomphionema setiforme sp. nov. female paratype.A. overall view, showing the two opposed and reflexed ovaries (arrow); B. reproductive system, showing vulva (arrow) and two opposed and reflexed ovaries. Scale bars:A = 100 µm. B = 20 µm.

FIGURE 4. Paracomesoma longissimum sp. nov. male holotype (A, B) and male paratype (C, D, E). A. lateral view of anterior portion, showing the cervical setae and excretory system (arrow); B, D. lateral view of posterior portion, showing the long spicules, plate-like gubernaculum and papilliform precloacal supplements (arrow); C. lateral view of anterior portion, showing the conical buccal cavity, unequally long cephalic setae (arrow) and multispiral amphideal fovea (arrow); E. high magnification drawing of spicules and gubernaculum (arrow). Scale bars: A, B, D = 30µm, C, E = 20µm.

FIGURE 5. Paracomesoma longissimum sp. nov., male holotype (A–C) and male paratype (D). A, B. lateral view of anterior end, showing the conical buccal cavity, unequally long cephalic setae, multispiral amphideal fovea (arrow) and the cervical setae (arrow); C. lateral view of tail end, showing the plate-like gubernaculum and papilliform precloacal supplements; D. lateral view of cloacal region, showing the long spicules and papilliform precloacal supplements. Scale bars: A, B: 10 µm; C, D: 20 µm.