Psammonema Verschelde & Vincx, 1995

Genus Psammonema Verschelde & Vincx, 1995 View in CoL

Type species

Psammonema ovisetum Verschelde & Vincx, 1995 .

Diagnosis (emended from Muthumbi & Vincx 2016)

Annulated cuticle with fine lateral alae beginning posterior to, or at level of, pharyngeal region. Females usually with both long slender somatic setae and short somatic setae. Six inner and six outer labial sensilla on anterior portion of the cephalic capsule, four cephalic sensilla on main portion of cephalic capsule; additional sub-cephalic setae may also occur on main portion of cephalic capsule. Sexual dimorphism usually present in shape and size of amphidial fovea; amphidial fovea located anteriorly on main portion of cephalic capsule, may extend to anterior portion of cephalic capsule. Buccal cavity with one large dorsal tooth and two ventrosublateral teeth; denticles usually present. Pharyngeal lumen not strongly cuticularized; posterior pharyngeal bulb present, may be elongated and partitioned by discontinuities in pharyngeal tissue. Precloacal supplements usually present (thorn-like or cuticular swellings).

Remarks

When erecting the genus, Verschelde & Vincx (1995) noted that Psammonema differs from the closelyrelated genus Pseudochromadora Daday, 1899 in the following traits: 1) position and shape of the lateral alae (narrower in Psammonema and beginning at level of pharynx instead of posterior to it), 2) anterior position of the amphids on the cephalic capsule (compared to central position in Pseudochromadora ), 3) presence of denticles in the buccal cavity (absent in Pseudochromadora ), 4) fine cuticular pharyngeal lumen (thick lumen cuticle with conspicuous valves in Pseudochromadora ), 5) elongated tripartite pharyngeal bulb (bipartite in Pseudochromadora ) and 6) two or three types of somatic setae in females (no differentiation in Pseudochromadora ). Another difference between these genera is the absence of copulatory and/ or postcloacal thorns in Psammonema (present in Pseudochromadora ). The distinction between the two genera, however, has become less clear with the subsequent description of additional Psammonema species (Jacob et al. 2016; Muthumbi & Vincx 2016). The difference in lateral alae position no longer applies, as it is located posterior to the pharynx in Psammonema waweri Muthumbi & Vincx, 2016 . The latter species also lacks denticles like species of Pseudochromadora . A prolonged tripartite bulb is only found in P. ovisetum , and not in the other Psammonema species. This leaves amphid position, pharyngeal lumen cuticularisation, differentiation of somatic setae in females and presence/ absence of copulatory and postcloacal thorns as the characters that can be used to differentiate between the two genera. In the new species, the amphidial fovea is positioned anteriorly on the main portion of the cephalic capsule, the pharyngeal lumen is not cuticularised and copulatory and postcloacal thorns are absent, which agrees with the diagnosis of Psammonema . On the other hand, females of the new species have only one type of somatic setae, which agrees with the diagnosis of Pseudochromadora . On balance, my assessment is that the new species should be classified with Psammonema .

List of valid species

P. ovisetum Verschelde & Vincx, 1995

P. kuriani Jacob, Anilkumar, Philip, Rayaroth, 2016

P. waweri Muthumbi & Vincx, 2016