Drilonereis orensanzi, 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 : 760-762

Drilonereis orensanzi n. sp.

( Fig. 8 )

Material examined. Holotype: AM W.44913, MI QLD2429 (1), fixed in formalin few median chaetigers fixed in ethanol. Paratypes: AM W.44797 (1), fixed in formalin; AM W.44923 (1), fixed in formalin few median chaetigers fixed in ethanol.

Measurements. Table 2.

Description. Live specimens whitish to yellowish with internal red hues due to blood ( Fig. 8 A). Specimens fixed in formalin dark brown with lighter (yellowish to white) anterior and posterior ends ( Fig. 8 B–E).

Body long, slender, about the same width along its whole length slowly tapering towards posterior end ( Fig. 8 A, E); dorsoventrally rounded, dorsal side as convex as ventral. Chaetigers becoming longer and narrower towards posterior region, some longer than wide, all with a transverse median groove, appearing to be double ringed.

Prostomium as long as to longer, about as wide and as half as deep as peristomium; proximal end deeper than distal; triangular, anteriorly tapering, dorsoventrally flattened; median longitudinal groove present on dorsal and ventral sides, dorsal groove extends to anterior peristomial ring ( Fig. 8 B–D). Eyes absent. Peristomium double ringed, first twice as long as second, longer dorsally than ventrally ( Fig. 8 B–D). Margin between prostomium and peristomium inconspicuous dorsally ( Fig. 8 B).

Mandibles forward to maxillae in pharyngeal bulb while retracted; reduced, subtriangular, round anterior end, plates diverging posteriorly ( Fig. 8 F). Maxillae dorsal carrier narrower at anterior end than beginning of the furcula; ventral carrier falcate ( Fig. 8 G). Maxillae with four pairs of plates symmetrical regarding shape and size ( Fig. 8 G–K). MxI distally falcate with 2–3 inconspicuous teeth at the base ( Fig. 8 K). MxIV inconspicuous poorly sclerotized ( Fig. 8 I). Maxillary formula: (1, 2) + (1, 3), 7 (8) + 8 (9), 4 (3) + 5 (3), 2 + 2. Most teeth fang shaped.

Parapodia inconspicuous in anterior region, becoming more conspicuous towards posterior end. Pre-chaetal lobe rounded, becoming longer than chaetal lobe in posterior region. Post-chaetal tapering (digitiform), twice to two and half times as long as chaetal lobe, longest in median to posterior chaetigers. Notopodial cirri absent.

Neuroaciculae 2 to 3 present, mucronate. Two to four limbate capillary present in supra and subacicular position, 2–3 in anterior and posterior, 3–4 in most neuropodia ( Fig. 8 L, M). Acicular spine chaeta straight on one side and tapering on the other, in neuropodia ventralmost position along most of the body, about half as long to as long as post-chaetal lobe ( Fig. 8 M).

Pygidium with a pair of button shaped structures ( Fig. 8 E).

Variation. There is little variation among examined specimens. The main variation is the number of teeth in MxII and III.

Remarks. The teeth at the base of MxI are very inconspicuous. Thus, we are not sure about the exact number of teeth. It was not possible to observe MxIV in W44797, since the maxillae broke during mounting. It is not clear if the button shaped structures are the complete pygidial cirri or just remains of those.

Drilonereis orensanzi n. sp. belongs to the group of species with four maxillary plates, MxI basally dentate and reduced mandibles present, which also includes D. australiensis , D. cylindrica Hartman, 1951 , D. longa Webster, 1979 , D. pinnata Treadwell, 1921 , D. robustus ( Moore, 1903) and D. similis Treadwell, 1921 (Table 3). Among these, it is most similar to D. australiensis , D. longa and D. pinnata . It shares similar prostomium and peristomium with the first two, mandible shape with D. longa and inconspicuous teeth at the base of MxI and two teeth in MxIV with D. australiensis and D. pinnata .

However, these three species have contrasting features with those of D. orensanzi n. sp. Drilonereis australiensis and D. pinnata have distinct mandible shape, respectively, single plate mandible similar to an upside down heart of spade and subtriangular mandible with parallel plates and flat anterior end. Drilonereis longa has conspicuous teeth at the base of MxI and aciculae chaetae clearly longer than post-chaetal lobe. Drilonereis pinnata has conspicuous anterior parapodia, a unique feature among species of the genus. Thus, D. orensanzi is differentiated from all other species described for the genus in its unique combination of prostomium, peristomium, maxillae, mandible features as well as of acicular spine chaeta shorter than post chaetal lobe (Table 3).

Etymology. The name is in honour of José María (Lobo) Orensanz, scientist who has published important studies on the systematics of Eunicida .

Habitat. Intertidal sand bottom.

Type locality. Lizard Island, Casuarina Beach.

Figures

FIGURE 8. Drilonereis orensanzi n. sp. A. Whole body of live specimen; B. Anterior end, dorsal view, arrow to median groove; C. Anterior end, ventral view, arrow to median groove; D. Anterior end, lateral view; E. Posterior end, dorsal view; F. Mandibles, ventral view; G. Maxillae and carriers, dorsal view, arrow at beginning of the furcula; H. MxI and II, dorsal view, rectangle highlights region magnified in K; I. Right MxIII and MxIV, ventral view; J. Left MxIII; K. Base of MxI, detail of inconspicuous teeth; L. Right parapodium 34; M. Right parapodium 149, arrow to chaeta acicular spine. A – D, W. 44797; E – H, K – N, AM W. 44913; I – J, AM W. 44923.