Genus Nais Müller, 1773

Nais communis Piguet, 1906 / Nais variabilis Piguet, 1906

Nais communis Piguet, 1906: 247 .

Nais variabilis Piguet, 1906: 253 .

MATERIAL EXAMINED. — Station 7: slide 10.357.04(c); station 12: slide 10.349.01(b); station 14: slide 11.251.03(a); station 25: slides 11.264.07, 11.264.08; station 28: 11.265.03; station 30: slide 10.349.06(a); station 37: slides 11.259.04, 11.259.05; station 38: slide 11.258.03(a,b); station 49: slide 10.351.02; IRScNB, I.G. 32392.

REMARKS

Recent molecular data have shown that these two species are actually an assemblage of at least five distinct evolutionary lineages, representing a morphological continuum covering the variation of the Nais communis / variabilis complex (Envall et al. 2012). No morphological revision of this complex has been carried out so far, which prevents an identification of these cryptic species otherwise than with molecular data. Although morphologically very similar, N. communis and N. variabilis are said to be different in their ability to swim ( N. variabilis) or not ( N. communis), and in an abrupt or gradual dilatation of oesophagus from VII ( N. variabilis and N. communis, respectively) (Piguet 1906). On preserved material, only this last character can be assessed. In spite of uncertainties about the exact nature of both species, we tentatively distinguish our taxa (Table 1) on the basis of this character, pending an assessment of its discriminatory value in the future.