Oenone

Zanol, Joana & Ruta, Christine, 2015, New and previously known species of Oenonidae (Polychaeta: Annelida) from Lizard Island, Great Barrier Reef, Australia, Zootaxa 4019 (1), pp. 745-772 : 768-769

Oenone sp. 1

( Fig. 11 )

Material examined. AM W.44342, MI QLD 2359 (1), fixed in formalin. Measurements. Table 2.

Description. Specimen fixed in formalin beige ( Fig. 11 A–C).

Body evenly tapering towards posterior end, anteriormost 15 chaetigers widest; dorsoventrally rounded.

Prostomium longer, as wide and as deep as peristomium; anteriorly rounded, dorso-ventrally inflated ( Fig. 11 A–C). All antennae digitiform not covered by anterior edge of peristomium in fixed specimens, evenly spaced, about same length, reaching posterior to eyes. Two pairs of dorsal eyes arranged in line at the posterior region of the prostomium, lateral larger bean shaped, median round with pigments scattered around it; median eyes closer to each other than to lateral eyes ( Fig. 11 A). One pair of ventral eyes at the ventroanterior end of prostomium, smaller than dorsal median eyes ( Fig. 11 B). Peristomium single ring, dorsally shorter than ventrally ( Fig. 11 A).

Mandibles cutting plates bifid, inner portion evenly tapering, lateral portion tapering abruptly at distal end ( Fig. 11 D). Maxillae carriers broke during mounting. Maxillae with five pairs of plates; shape of plates asymmetric ( Fig. 11 E, F). Left MxI distally falcate. Right MxI shorter than left one, two anteriormost teeth fang like, teeth decrease in size from anterior to posterior. Anteriormost tooth of MxII, MxIII and MxIV fang like. Maxillary formula: (1, 8) + 6, 10 + 11, 14 + 10, 11 + 9, 1 + 1.

Pre-chaetal lobe shorter and post-chaetal longer than chaetal lobe; post-chaetal 1.5 times as long chaetal lobe, tapering to round distal end, widest at anterior end. Chaetal lobe pointed to round. Notopodial cirri digitiform; shorter than post-chaetal lobe ( Fig. 11 G); best developed at anterior chaetigers, by the end of fragment cirri are inconspicuous.

Notoaciculae present; at least 3 in anterior and 2 in posterior notocirri. Neuroaciculae 2 to 4 present. Capillary present in supra and subacicular position; decrease in length from dorsal to ventral; decrease in number from anterior to posterior; anterior neuropodia with 6–8, median and posterior 5–2 capillary ( Fig. 11 G, H). Ventral bidentate subacicular hook ( Fig. 11 I, J) starting at chaetiger 11, one in more anterior and two in more posterior neuropodia; both teeth directed distally.

Pygidium not observed.

Remarks. Oenone sp. 1 shares striking unique similarities with Halla sulfurea Langerhans 1880 , described from a specimen from Madeira Island (North Atlantic Ocean), such as placement of antennae and eyes, ventral eyes and shape of mandible. However, H. sulfurea can be distinguished from Oenone sp. 1 by the presence of a doubled ringed peristomium, digitiform and longer antennae, round lateral eyes, right MxI short with no anterior fang shaped teeth and minute teeth in MxIV.

We identified our specimen as Oenone based in its single peristomial ring and the lack of anterior peristomial notch, which contrast with Halla species that have a double ringed peristomium and an anterior peristomial notch. Halla sulfurea is also distinguished from other Halla species in the presence of ventral eyes and lack anterior peristomium notch. This led Crossland (1924) to question its validity. We question here its generic identification.

The shared unique features between Oenone sp. 1 and H. sulfurea , including their small size, may be due to the fact that both are, probably, juveniles. Our knowledge on the development of Oenone and Halla species is poor. Thus, we prefer not to take any further conclusion and to be conservative, leaving the Lizard Island specimen unidentified for now.

Habitat. Coral rubble, 6–12 m deep.

Figures

FIGURE 11. Oenone sp. 1. A. Anterior end, dorsal view; B. Anterior end, ventral view; C. Anterior end, lateral view; D. Mandibles, ventral view; E. Right MxI – MxV; F. Left MxI – MxV, MxII – MxIV broke during mounting; G. Right parapodium 8; H. Left parapodium 19; I. Bidentate subacicular hook, parapodium 19; J. Bidentate subacicular hook, parapodium 40. A – J, AM W. 44342.