Nicidion Kinberg, 1865

Zanol, Joana, Hutchings, Pat A. & Fauchald, Kristian, 2020, Eunice sensu latu (Annelida: Eunicidae) from Australia: description of seven new species and comments on previously reported species of the genera Eunice, Leodice and Nicidion, Zootaxa 4748 (1), pp. 1-43 : 38

Nicidion Kinberg, 1865

Description (features in bold are exclusive of this genus but not necessarily present in all species). Prostomium anteriorly round, with three antennae and a pair of palps; prostomial appendages irregularly articulated; pair peristomial cirri present or absent. Mandibles flat, cutting plates medially connected. Maxillary plates paired MxI, MxII, Mx IV, MxV and unpaired MxIII, MxVI absent; each species with limited variability in numbers of maxillary teeth. MxII has teeth on anterior end only (at most on anterior half). Branchiae absent or present, usually single filaments or pectinated. Parapodia with well-developed neuropodia; notopodia represented by bases of notopodial cirri. Neuropodial chaetal lobe pointed from second quarter of the body to posterior end. Ventral cirri usually with round basal glandular inflated region at least in median chaetigers; distally tapering to distinct tips or elongated ridge. Notopodial and ventral cirri decrease towards posterior end. Internal notopodial aciculae present in anterior chaetigers. Neuropodial aciculae single or multiple, distally often projecting from neuropodia; most commonly tapering to blunt straight tips, but also hammer head and mucronate; dark. Notopodial chaetae absent. Neuropodial chaetae in, usually, two distinct fascicles; supra-acicular fascicle consisting of limbate chaetae usually in two or more oblique rows and thin pectinate chaetae usually anterior or dorsal to limbate chaetae. In median and posterior chaetigers, thin pectinate chaetae with wide blade and placed dorsal to aciculae. Subacicular fascicle usually located slightly posterior to dorsoventral midline, consisting of true-compound bidentate falciger chaetae; usually arranged in two or more, oblique rows. Chaetae composition usually similar in most chaetigers, but vary in shape and number along the body, limbate and compound falcigers chaetae often reduced in numbers in far posterior chaetigers. Subacicular hooks bidentate present from anteromedian chaetigers; occurring singly (replacement hooks often visible) or in pairs; dark along most of its distribution, with darkest colour shade on subacicular hooks restricted to distal half or distal end of the hook from second quarter to the end of the body in most species. Subacicular hooks at posteriormost chaetigers yellow. Dorsal pygidial cirri present; ventral pygidial cirri absent or present.

Remarks. Nicidion has recently been resurrected to include species considered to belong to Eunice and Marphysa sensu lato ( Zanol et al. 2014). Its type specie is Nicidion cincta Kinberg, 1865 . Darkest colour shade on subacicular hooks at distal half or distal end of the hook from mid chaetiger on the second quarter of the body to the end of the body in most species is an exclusive feature of this genus but are not present in all species. Among traditional Eunice sensu lato species, all abranchiated species are now placed in Nicidion . But not all species in the genus are abranchiated. Notopodial and ventral cirri tend to decrease towards posterior end, as well as neuropodial lobes. Thus in posterior parapodia, aciculae and subacicular hook are conspicously observed even under stereomicroscope.