Draconematidae (Nematoda) from cold-water corals in the Porcupine Seabight: The genus Cygnonema Allen & Noffsinger, 1978

Two new and closely related species of the genus Cygnonema Allen & Noffsinger, 1978 are described from a cold-water coral degradation zone in the Porcupine Seabight (NE Atlantic). Both species differ from C. steineri Allen & Noffsinger, 1978 by more pronounced pharyngeal and posterior swellings, a smaller body, a shorter pharynx in relation to body length, a higher number of CAT, and by the absence of a dorsal tooth. Cygnonema verum sp. n. differs from C. belgicae sp. n. by its greater body length, the relatively larger head capsule, a higher number of CAT, a more anteriorly positioned anteriormost laterodorsal CAT, a higher number of PAT, by the external labial sensilla being setiform, a higher number of subcephalic setae, and by a more anterior position of the amphidial fovea on the head capsule. Males of C. verum sp. n. are easily recognised by the presence of two large subventral, precloacal corniform setae. They also differ from males of C. belgicae sp. n. in the smaller amount of cytoplasm in the sperm cells, a knob-like capitulum, and a relatively shorter tail tip. The diagnosis of Cygnonema is emended, a dichotomic identification key to the three species is provided, and their biogeography is discussed.