Orbiniidae Hartman, 1942

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 : 8-9

Family Orbiniidae Hartman, 1942

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

Diagnosis. 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 indistinct body regions, or body regions absent. 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 of which the first is a true peristomial segment, with second and third, when present representing achaetous segments ( Fauchald & Rouse, 1997). Paired cirriform and ciliated branchiae located mid-dorsally between the 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 to and medial to branchiae in some thoracic and abdominal parapodia. Notopodia simple, 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 stomach papillae. Abdominal neuropodia extending laterally and dorsally, usually bilobed; ventral cirrus often present; ventral flange may be present. Lateral organ sometimes present between noto- and neuropodia. Notosetae including 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 including capillaries and sometimes flail setae with hoods or mucrons on their tips; imbedded aciculae usually present; protruding present on some genera. Pygidium simple, collarlike, sometimes with several long filamentous anal cirri.

Remarks. This diagnosis is condensed from Hartman (1957) who provided the most comprehensive modern review of the family together with summaries of the historical literature. Hartman (1957) also diagnosed most of the genera and provided a comprehensive glossary of morphological terms. Readers are referred to Hartman’s monograph for further details. Apart from micromorphology now evident in the scanning electron micrographs, the morphological criteria defined by Hartman are still relevant. However, patterns of chaetogenesis of furcate and crenulated capillary setae in orbiniids revealed by Hausam & Bartolomaeus (2001) provide important clues for understanding the relationship of orbiniids with other polychaete families. Hoffman & Hausam (2007) analyzed the setal fascicle arrangement of orbiniids and found little similarity with other families suggesting another approach for using morphology to understand phylogeny among polychaete families. Further, several new setal characters have been identified in the present study that permit a finer resolution between species.