Orbiniidae Hartman 1942

Family Orbiniidae Hartman, 1942

Type genus: Orbinia Quatrefages, 1866, designated by Hartman, 1942.

Diagnosis. (modified from Blake 2017). Body elongate, usually divided into a wide, dorsoventrally flattened thoracic region formed of firm, muscular segments and a posterior abdominal region rounded in cross-section and composed of soft, fragile segments bearing dorsally elevated parapodia, or abdominal parapodia not elevated; bodies usually with distinct body regions, or body regions indistinct. Prostomium of variable shapes, with anterior margin ranging from acutely pointed to bluntly rounded; 1–2 pair of eyespots sometimes present, but usually absent; paired nuchal organs present. Proboscis soft, eversible, saclike without armature, sometimes dendritically branched when everted. Peristomium composed of 1–3 achaetous rings; juveniles with two rings often with only one as adult. Paired cirriform and ciliated branchiae located mid-dorsally between notopodia, beginning either on or just posterior to thoracic region, continuing to posterior end; or branchiae entirely absent. Small dorsal sense organs sometimes present anterior and medial to branchiae in some thoracic and abdominal parapodia. Notopodia simple, with fingerlike postsetal lobes; sometimes divided or forked. Interramal cirri sometimes present between notopodia and neuropodia of posterior thoracic and/or abdominal segments. Neuropodia well developed in thoracic region, sometimes forming elevated ridges bearing numerous setae; one to many postsetal lamellae often present, sometimes continuing ventrally as additional subpodial or stomach papillae. Abdominal neuropodia extending laterally and dorsally, usually bilobed; ventral cirrus often present; ventral flange may be present. Lateral ciliated organ sometimes present between noto- and neuropodia. Notosetae include capillaries, flail setae, and furcate setae; modified spines sometimes present in abdominal notopodia. Thoracic neurosetae may include crenulated capillaries, blunt-tipped crenulated setae, crenulated or smooth uncini, and modified spines; or any combination of capillaries, uncini, and spines. Abdominal neurosetae include capillaries and flail setae; imbedded aciculae usually present, protruding on some genera. Multidentate swan hooks or bidentate hooks or crotchets known from two genera. Pygidium simple, collar-like, often with 2–4 long filamentous anal cirri.

Remarks. A few edits to the diagnosis of Blake (2017) serve to update minor details. However, this diagnosis essentially follows the more extensive family definition of Hartman (1957). With the inclusion of the genus Questa, orbiniids now contain a few species having bidentate hooks or crotchets similar to those found in some paraonids (Giere et al. 2008). The multidentate swan hooks found in Proscoloplos are a more complex manifestation of hooked setae. When present, furcate setae of orbiniids typically have two long tynes from which numerous thin needles or spines project into the space between forming a web. In species of Questa, however, two long, thick tynes have either one or two shorter and thinner basally attached prongs arising between them.