Orbiniella Day, 1954

Meca, Miguel A., Kongsrud, Jon Anders, Kongshavn, Katrine, Alvestad, Tom, Meißner, Karin & Budaeva, Nataliya, 2024, Diversity of Orbiniella (Orbiniidae, Annelida) in the North Atlantic and the Arctic, ZooKeys 1205, pp. 51-88 : 51-88

Orbiniella Day, 1954

Falklandiella Hartman, 1967: 109. Fide Parapar et al. 2015: 333.

Orbiniella – Parapar et al. 2015: 333; Blake 2017: 109; Blake 2020: 38; Blake 2021: 99.

Type species.

Orbiniella minuta Day, 1954 , by monotypy.

Diagnosis

(emended from Blake 2021). Body usually elongated, not divided into thorax and abdomen. In some species segmental size can change gradually between anterior and posterior body. Prostomium broad or elongate with rounded anterior margin. One pair of nuchal organs usually present, sometimes pigmented. Eyes present or absent. Peristomium usually bearing two segments. Secondary annulation present with segments being uniannulate, biannulate, triannulate, or quadriannulate. Parapodia biramous with only simple postchaetal lobes, or these entirely absent. Capillary noto- and neurochaetae always crenulated or weakly crenulated with pointed tips; prominent acicular spines present in neuropodia and, usually, also in notopodia; furcate chaetae absent. Branchiae absent. Pygidium with two or four anal lobes, with or without cirri.

Remarks.

Blake reviewed Orbiniella in his monographs from 2017, 2020 and 2021, updating its generic diagnosis and the checklist of species. He reported segmental annulation pattern as a key character to separate Orbiniella species ( Blake 2020), but this character was not included in the generic diagnosis. Similarly, Blake (2020) also reported and illustrated the anal lobes and cirri in the species descriptions without including them in the diagnosis. We consider these two characters, in combination with other characters discussed below, of high diagnostic value to separate Orbiniella from other orbiniid genera and here we include them in the generic diagnosis of Orbiniella .

The main diagnostic characters to identify Orbiniella species are absence of branchiae along with presence of acicular spines through the whole body, secondary annulation, and pygidium with or without anal cirri. Microrbinia linea Hartman, 1965 , and some species of Questa also do not have branchiae; however, the former can be separated from Orbiniella by the presence of unusual long and serrated spines and the latter by the presence of bi- or tridentate crotchets. The other orbiniid having acicular spines through the whole body is Methanoaricia dendrobranchiata Blake, 2000 . However, this species has very specialised morphology (i. e., elongate and narrow prostomium, long branched branchiae, long and cirriform parapodial lobes and pygidium with many anal cirri) and is easily distinguished. Secondary annulation has been reported also in some species of Questa and in Microrbinia linea Hartman, 1965 , but they can be separated from Orbiniella by their unique chaetae mentioned before. Most orbiniids bear two or four (rarely many) anal cirri in the pygidium, and only some Orbiniella and Questa show no anal cirri, being a unique feature of both genera.