Oenone ventrioculata, Zanol, Joana & Ruta, Christine, 2015

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 : 766

Oenone ventrioculata n. sp.

( Fig. 10 )

Material examined. Holotype: AM W.44002, MI QLD 2341 (1), fixed in ethanol. Paratype: AM W.44354, MI QLD 2371 (1), fixed in formalin, few median chaetigers fixed in ethanol.

Measurements. Table 2.

Description. Live specimens yellow ( Fig. 10 A–C, G). Specimens fixed in formalin beige, fixed in ethanol yellow ( Fig. 10 D–F, H). All live specimens have round prostomium and round body ( Fig. 10 A–B). Body long, slender, evenly tapering towards anterior and posterior ends, median region widest; dorsoventrally rounded, dorsal side around twice as deep as ventral.

Prostomium longer, about as wide and half as deep as peristomium, proximal end deeper than distal; anteriorly rounded, dorso-ventrally flattened ( Fig. 10 D–F). All antennae tapering to digitiform covered by anterior edge of peristomium in fixed specimens, about same length, reaching posterior to median eyes ( Fig. 10 A, D, F). Two pairs of dorsal eyes arranged in line at the posterior region of the prostomium, lateral larger round to elongated, median round; median eyes closer to each other than to lateral eyes ( Fig. 10 A, D). One pair of ventral eyes at the ventroanterior end of prostomium, smaller than dorsal median eyes ( Fig. 10 B, E). Peristomium single ring dorsally, double ringed ventrally, anterior dorsal edge complete ( Fig. 10 A, B).

Mandibles with cutting plates diverging anteriorly and converging posteriorly, bear an inner conspicuous tooth; mandible carriers longer than mandible cutting plates ( Fig. 10 I). Maxillae dorsal carrier anterior end as wide as beginning of the furcula ( Fig. 10 J); ventral carrier not observed. Maxillae with five pairs of plates; shape of plates asymmetric ( Fig. 10 J, K). Left MxI distally falcate. Right MxI shorter than left one, anteriormost tooth fang like, teeth decrease in size from anterior to posterior ( Fig. 10 K). Anteriormost tooth of left MxII and both MxIII and MxIV fang like. In right MxII, two anteriormost teeth fang shaped placed side by side, most lateral one smaller and appears to be an independent plate under superficial observation. Maxillary formula: (1, 6) + 6 (7), 8 (7) + 9 (7), 6 (5) + 6, 5 (7) + 5, 1 + 1.

Pre and post-chaetal lobe longer than chaetal lobe; pre-chaetal rounded; post-chaetal widest at anterior end, twice as long a pre-chaetal. Notopodial cirri digitiform with narrow base, flattened in anterior chaetigers; around as long as post-chaetal lobe in most of the body, shorter in posterior chaetigers.

Notoaciculae present, at least 1 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. 10 L, M). Ventral bidentate subacicular hook starting at chaetiger 21 (14), one in more anterior and two in more posterior neuropodia; proximal teeth laterally directed ( Fig. 10 M, N).

Pygidium with a pair of dorsal and ventral cirri placed laterally and as long as two posteriormost chaetigers ( Fig. 10 H). Dorsal cirri digitiform. Ventral cirri wide dorsoventrally, about twice as wide as dorsal.

Variation. In the paratype, the antennae are triangular, reaching beyond the anterior end of the lateral eyes. Lateral eyes vary from rounded to elongated. In elongated eyes, pigments are loosely distributed but more concentrated in an anterior circle similar to lateral round eyes. Median notopodial cirri are shorter than postchaetal lobe, which is almost inconspicuous in poorly preserved median region.

Remarks. Many of the anterior chaetae are broken in the holotype. Therefore, the distribution of bidentate hooks may start earlier than observed.

This species differs from the other Oenone species in having the right MxI with an anteriormost tooth larger than the other teeth in the plate and a pair of ventral eyes at the anterior end of the prostomium. Similar MxI has been described for one specimen from Zanzibar Archipelago ( Tanzania) identified as O. fulgida ( Crossland 1924 pp. 88 fig. 108). Shape and placement of antennae in the paratype are similar to those in Haswell (1886) illustration of Halla australis . However, proportions and placement of the eyes do not match to what was observed here. Both species also differ in the shape of MxI.

Etymology. Name refers to pair of ventral eyes at the anterior end of the prostomium.

Habitat. Coral rubble, 9–16 m deep.

Type locality. Lizard Island, reef between Bird and South Islands.

Figures

FIGURE 10. Oenone ventrioculata n. sp. A, G. Anterior end of live specimens, dorsal view; B. Anterior end of live specimen, ventral view; C. Whole body of live specimen; D. Anterior end, dorsal view; E. Anterior end, ventral view; F. Anterior end, lateral view; H. Posterior end, dorsal view; I. Mandibles, ventral view; J. Maxillae and carriers, arrow at beginning of the furcula; K. Maxillae; L. Right parapodium 17, anterior view; M. Right parapodium 20, anterior view; N. Bidentate subacicular hook, parapodium 31. A – F, H – K, M, AM W. 44002; G, L, N, AM W. 44354.