Type species. Orbiniella minuta Day, 1954
Orbiniella Day, 1954: 22, Fig. 3 G–K.
Falklandiella.— Hartman 1967: 109, Fig. 35.
Orbiniella.— Fauchald 1977: 16; Solís-Weiss & Fauchald 1989: 781; Buzhinskaja 1993: 77, Figs. 1–3; Gillet 1999: 592, Figs. 1–2.
Diagnosis. Body not divided into thorax and abdomen, prostomium rounded. Eyes present or absent. Two peristomial annuli. Chaetigerous segments without branchiae or parapodial lobes; chaetae including crenulated capillaries and simple acicular spines. Noto- and neuropodial capillaries either smooth, with two rows of wide teeth along the margins, or with transverse rows of short spines. Teeth sometimes bearing long hairs at distal tips. Short and thick acicular spines (smooth or barbed) maybe present in both parapodial rami or only in neuropodia. Pygidium with two or four lobes, with or without cirri.
Remarks. Originally, Day (1954) did not provide a diagnosis of the genus Orbiniella, which is later provided by Fauchald (1977) and more recently by Solís-Weiss & Fauchald (1989), Buzhinskaja (1993) and Gillet (1999). The diagnosis followed here is that proposed by Buzhinskaja (1993), which has been slightly modified to avoid ambiguous terms such as “first two segments”; those refer to the two achaetous anterior rings. Furthermore, we consider that the pygidium may be either bilobed (as referred for previously described species) or four-lobed (the new species described herein).
There has also been confusion over the location of the peristomium and first segment in the Orbiniidae in general (Rouse 2002) and in Orbiniella in particular. Thus, genera of the Microrbiniinae Blake, 2000 have two annuli between the prostomium and the first chaetiger. Some authors consider that one of them is an “achaetous segment” (Day 1977; Fauchald 1977; Solís-Weiss & Fauchald 1989); alternatively, the peristomium would be constituted by two rings (Blake 1996). We consider that the latter would be more plausible; however, using the number of peristomial rings for separating genera or species may be not a reliable character (Blake 2000). Furthermore, the division of body into thorax and abdomen through transitional segments and presence of furcate chaetae does not seem appropriate to characterize the genus Orbiniella (Buzhinskaja 1993) and therefore O. drakei should not be included in this genus. Likewise, the presence of branchiae in O. branchiata suggests that this species should be referred to other genus (Blake 2000). Buzhinskaja (1993) also suggests that Falklandiella annulata should be transferred to Orbiniella, according to the original description and drawings by Hartman (1967). Blake (2000) considers it as valid although Fauchald (1977) places this genus as incertidae sedis but still recognising that resembles the orbiniids in chaetal features.