Polyeunoa McIntosh 1885

Polyeunoa McIntosh, 1885

Type species. Polyeunoa laevis McIntosh, 1885.

Diagnosis. Body long, with about 70 segments or more. Elytra at least 15 pairs, on segments 2, 4, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 26, 29, 32, with or without additional, sporadically and irregularly arranged pairs of elytra. Elytra nearly covering dorsum or leaving middorsum uncovered; most of posterior region of body uncovered. Prostomium bilobed with cephalic peaks poorly developed or absent; with three antennae; lateral antennae inserted ventrally to median antenna. Notopodia with prominent, digitiform acicular lobe; neuropodia with prominent, subtriangular acicular lobe, tip not extended to supra-acicular process; tips of noto- and neuroacicula penetrating epidermis. Notochaetae few, about as stout as neurochaetae, with blunt tip; neurochaetae numerous, with uni- or bidentate tip.

Remarks. Pettibone (1969) discussed the differences of Polyeunoa McIntosh, 1885 and Hololepidella Willey, 1905 and other related genera in detail. Therefore, we will focus here on the distinction from other relevant genera in this context, i.e. Polynoe Savigny in Lamarck, 1818 (with regard to Polynoe thouarellicola Hartmann-Schröder, 1989, junior synonym of Polyeunoa laevis), Enipo Malmgren, 1866 (with regard to Enipo rhombigera Ehlers, 1908, junior synonym of P. laevis), Neopolynoe Loshamn, 1981 (genus attributed to Polynoe antarctica Kinberg, 1858 herein), and Parapolyeunoa n. gen. (new genus established herein for Hololepidella flynni Benham, 1921). The variability in the number of pairs of elytra (15 or more), as described for Polyeunoa laevis below, might be problematic when specimens of P. laevis show exactly 15 pairs, like in specimens originally described as Polynoe thouarellicola. But, due to its prominent notopodium, Polyeunoa is easily distinguished from Polynoe which has a rather short, conical notopodium.

Differentiation of Polyeunoa and Enipo is also rather easy due to the absence of notochaetae tapering to a capillary tip in Polyeunoa, which is a typical character of Enipo.

As in Polyeunoa, the notopodium of Neopolynoe, is prominent, but Neopolynoe never shows more than 15 pairs of elytra. Only in the case of P. laevis having exactly 15 pairs of elytra might its differentiation from Neopolynoe be problematic. But the fact that Neopolynoe always has distinct cephalic peaks and a thick, stout supra-acicular process at the tip of the neuropodial acicular lobe versus cephalic peaks poorly developed or absent and tip of acicular neuropodial lobe not extended to supra-acicular process as in Polyeunoa allows a clear identification.

Parapolyeunoa n.gen., described below, is easily distinguished from Polyeunoa because of its obvious, distinct cephalic peaks and the presence of a supra-acicular process at the neuropodial tip.

For further details on distinctive characters see Table 1 and remarks related to species descriptions below.

The variability observed in some of the morphological characters of Polyeunoa, such as number of pairs of elytra or the presence/absence of dorsal tubercles (see description of P. la ev i s below) for example, suggests that the type species of the genus might represent a species complex. Currently the DNA-sequences of Polyeunoa and some other genera are analysed by two Italian colleagues, Stefano Schiaparelli and Maria Chiara Alvaro (University of Genova), but some more material has still to be checked before any definite conclusions can be drawn.