Maragnopsia, Leduc, 2016

Leduc, Daniel, 2016, One new genus and three new species of deep-sea nematodes (Nematoda: Microlaimidae) from the Southwest Pacific Ocean and Ross Sea, Zootaxa 4079 (2), pp. 255-271 : 265-268

Maragnopsia n. gen.

Etymology. The genus name is derived from the greek maragna (= whip) and opsia (= evening, night), and refers to the long and thin shape of the body and tail that characterises the type species, and the dark environment in which it lives.

Diagnosis. Maragnopsia n. gen. is characterised by a minute, non-cuticularised mouth cavity without teeth, an elongated posterior pharyngeal bulb 2.4–2.9 times longer than wide, a single outstretched testis, and a conicocylindrical tail 13–16 anal body diameters (abd) long.

Remarks. A minute buccal cavity without teeth has been described for the closely related genera Cinctonema Cobb, 1920 and Crassolaimus Kreis, 1929 . Both of these genera, however, are considered genera inquirenda due to lack of detailed descriptions ( Tchesunov 2014). A number of Microlaimus and Aponema species possess a single testis, although this trait is rare within Microlaimus (e.g., M. nanus and M. nympha ). Microlaimus capillaris was also described as having only one testis but in this case it is reflexed, and not outstretched as in Maragnopsia gen. n. An elongated posterior pharyngeal bulb (at least two times longer than wide) and long conico-cylindrical tail are unique traits within the Microlaimidae . All other microlaimid genera are characterised by a rounded, pyriform, or oval-shaped posterior pharyngeal bulb, which differ markedly in shape to the elongated bulb of Maragnopsia n. gen. A tail with a short conical portion is found in Microlaimus gerlachi , M. honestoides and M. pygmaeus but tail length in these species never exceeds 6 anal body diameters (abd).

The new genus shows superficial similarities with the family Linhomoeidae (Order Monhysterida ), due to the absence of teeth in the buccal cavity, cheilostoma apparently without longitudinal folds, circular amphids, outstretched ovaries, short spicules and long conico-cylindrical tail. Maragnopsia gen. n., however, lacks two key characteristics of the family Linhomoeidae , i.e., a narrow mouth opening surrounded by bulge of inner portion of lip region, and conspicuously elongated cardia. The head of Maragnopsia gen. n. is characterised by a slightly swollen, non-annulated apical portion, a feature found in the microlaimid genera Microlaimus and Aponema , but not in the family Linhomoeidae . Microlaimids are usually characterised by the presence of four cephalic setae in a separate circle from the often minute (rarely setose) outer labial sensillae and usually lack subcephalic setae, whereas linhomoeids often have setose outer labial sensillae and/or subcephalic setae. The absence of longitudinal folds in the cheilostoma of Maragnopsia gen. n. is probably due to the small size of the buccal cavity, which makes observations difficult. In addition, the cuticle of Maragnopsia gen. n. is annulated, a feature of the Microlaimidae , and not striated, as in the Linhomoeidae .