Aricia Savigny, 1820: 12, 35–36. Preoccupied. Type-species: A. sertulata Savigny, 1820, by monotypy.
Orbinia Quatrefages, 1866: 288.
Type-species: Aricia cuvieri Audouin & Milne-Edwards, 1833 (= Aricia sertulata Savigny), designated by Hartman 1942.
Diagnosis. Prostomium conical, pointed; peristomium with one achaetous ring. Branchiae from thoracic setigers (5–20). Posterior thoracic segments with postsetal lobes (2–many) and subpodial lobes (3–many), usually forming ventral encircling fringe of five or more lobes. Thoracic neurosetae including blunt uncini, crenulated capillaries and rarely subuluncini; heavy spear-like or brush-tipped spines absent. Abdominal neuropodia with flail setae.
Remarks. Three species— Orbinia swani Pettibone, 1957, O. riseri (Pettibone, 1957), and O. americana Day, 1973 —have been described and reported from the U.S. Atlantic coast. Each of these species was originally de- scribed from a single incomplete specimen. No specimens of O. riseri or O. americana were available in any of the new collections, but numerous specimens of O. swani were collected offshore on Georges Bank in the 1980s as part of the MMS long-term monitoring program. The specimens of O. swani include a range of sizes and a few complete specimens that provide additional details on the adult morphology as well as providing important information on morphological changes during growth.