Microrbiniinae Blake, 2000

Blake, James A., 2017, Polychaeta Orbiniidae from Antarctica, the Southern Ocean, the Abyssal Pacific Ocean, and off South America, Zootaxa 4218 (1), pp. 1-145 : 108

Subfamily Microrbiniinae Blake, 2000

Type genus. Microrbinia Hartman, 1965 , designated by Blake 2000.

Diagnosis. Body small, lacking distinct regions; parapodia lateral throughout, none shifted dorsally. Prostomium broad, bluntly rounded or more elongate and conical; nuchal organs present. Peristomium with 1–3 achaetous rings, separated from prostomium. Noto- and neuropodial postsetal lamellae reduced to short lobes. Bases of podia separated throughout; setal tori simple. Setae consisting of capillaries always present, blunt-tipped spines or uncini and swan hooks present or absent; furcate setae typically absent. Branchiae typically absent, rarely present, if present; simple throughout, oval to flattened with two longitudinal rows of cilia. Pygidium with few cirri or cirri absent.

Inclusive genera. Microrbinia , Orbiniella , Proscoloplos , and Pettibonella .

Remarks. Two genera, Orbiniella and Proscoloplos and seven species including two new species were encountered in the present study. The species and genera presently assigned to this subfamily are largely defined on negative characters including the absence of distinct body regions, unmodified posterior parapodia, and often the absence of branchiae. Modified setae are rare and when present are similar to the aciculae found in larger species of the Orbiniinae . Several described species are literally microscopic in size (1–3 mm long), approximating dimensions reported for post-larvae of other orbiniids (e.g., Okuda 1946; Blake 1980), suggesting that many species of this subfamily may be juveniles of species in other orbiniid genera. This does not apply to Microrbinia linea Hartman, 1965 , a small deep-water species off the U.S. Atlantic coast that Blake (1993) determined was sexually mature year round. Mature ova are also reported for Orbiniella andeepia , O. uniformis , and O. landrumae n. sp. in this paper, and O. nuda , and O. plumisetosa in previous reports (see Table 2; this study, see below). Reports of gametes or other evidence of sexual maturity in other species in this subfamily are rare.