Orbiniinae Hartman 1957

Subfamily Orbiniinae Hartman, 1957. Emended by Blake 2000.

Type genus. Orbinia Quatrefages, 1866, designated by Hartman 1957.

Diagnosis. (after Blake 2017). Body large, with distinct regions; parapodia lateral in thoracic region, typically shifted dorsally in abdominal region. Prostomium bluntly rounded to acutely pointed; nuchal organs present; eyespots present or absent. Peristomium with 1–2 achaetous rings, separated from prostomium. Noto- and neuropodial postsetal lamellae single, simple lobes to multiple lobes, sometimes branched; subpodial lobes and stomach papillae present or absent; interramal cirri present or absent. Setae including aciculae, capillaries, furcate setae, spines, uncini, modified spear-like setae, and flail setae. Branchiae typically present, rarely absent; branchiae usually single, rarely branched; oval to flattened, with two longitudinal rows of cilia and typical orbiniid structure with two blood vessels connected by numerous capillaries; branchiae of abdominal region thinner, more elongate than on thorax. Pygidium with several long filamentous anal cirri, or cirri absent.

Inclusive genera. Berkeleyia, Califia, Leitoscoloplos, Leodamas, Naineris, Orbinia, Phylo, Protoaricia, and Scoloplos.

Remarks. The subfamily Orbiniinae contains most of the better-known genera and species of Orbiniidae.

Genus Leitoscoloplos Day, 1977

Type-species: Haploscoloplos bifurcatus Hartman, 1957, designated by Day 1977

Diagnosis. (after Blake 2017). Prostomium pointed, conical; peristomium typically with one achaetous ring, but with additional superficial annulae on some species. Branchiae lacking, or present from middle, to posterior thoracic, transitional, or abdominal setigers. Posterior thoracic setigers with 0–2 postsetal lobes and 0–2 subpodial lobes; abdominal setigers with 0–4 subpodial papillae; stomach papillae rare, interramal cirri present or absent. Thoracic neurosetae including only crenulated capillaries. Without abdominal neuropodial spines, with 2–3 imbedded aciculae present or absent. Notopodial furcate setae present or absent in abdominal segments.

Remarks. The genus Leitoscoloplos differs from Scoloplos in lacking spines or uncini in thoracic neuropodia. However, this classification is likely to change with further study because Leitoscoloplos species appear to contain several distinct groups. Blake (2017) divided the genus into five groups (A–E), based largely on the presence and distribution of branchiae, as a practical means to separate groups of species to facilitate their identification. Presently, the genus consists of 32 species (Blake 2020), four of which have been encountered in the present study; one new species, L. pustulus n. sp. has also been identified. The five species occur in Groups B (branchiae present from middle to posterior thoracic setigers) and Group C (branchiae present from transitional segments between thoracic and abdominal segments). Interestingly, no species in the so-called L. kerguelensis group were encountered (Group D, with branchiae first present from anterior abdominal setigers). It appears as if Group D is largely limited to the southern hemisphere and Pacific Ocean. Among species of Leitoscoloplos encountered in the present study, three are taxa with an interramal cirrus between the noto- and neuropodia of abdominal segments: L. fragilis, L. obovatus, and L. robustus. In addition, L. pustulus n. sp. has a short interramal process in the same location. Thus four of five species of Leitoscoloplos along the Atlantic coast of the US have a distinct interramal cirrus or process. Species of Leitoscoloplos having this feature are rare elsewhere.

Of the five species of Leitoscoloplos encountered in the present study, two, L. obovatus and L. pustulus n. sp., are from upper continental slope depths, while the other three species are well known and range from intertidal or shallow water to shelf depths of less than 100 m. The five species covered in this paper are: