Microrbinia Hartman, 1965

Blake, James A., 2021, New species and records of Orbiniidae (Annelida, Polychaeta) from continental shelf and slope depths of the Western North Atlantic Ocean, Zootaxa 4930 (1), pp. 1-123 : 93

Genus Microrbinia Hartman, 1965

Type species: Microrbinia linea Hartman, 1965 , by monotypy.

Diagnosis: (Emended) Body long, threadlike; thoracic region with a few short uniannulate segments gradually transitioning to elongate (biannulate) abdominal segments. Prostomium conical, tapering anteriorly; with paired nuchal organs; eyespots absent. Peristomium a single asetigerous ring. Noto- and neuropodia with well-developed postsetal lobes; branchiae absent; parapodia lateral to dorsolateral, some notopodia directed dorsally, but not shifted on to dorsal surface in abdominal segments. Branchiae absent. Setae serrated or camerated capillaries throughout; posterior notosetae including unusual long serrated spines with curved tips; furcate and flail setae absent. Pygidium with four anal cirri. Males with conical gland-like dorsal organs on a few anterior abdominal segments. Females with 1–2 large, elongate eggs in one or two swollen abdominal segments.

Remarks: The genus Microrbinia is monotypic with the only known species, M. linea occurring on the U.S. Atlantic continental slope. The species is unusual among orbiniids in having conical gland-like structures on the dorsal surface of some anterior abdominal segments. These appear to be associated with males; females have one or two elongate swollen segments containing large eggs, but none of the gland-like dorsal organs. The unusual serrated spinous notosetae that occur in middle and posterior abdominal segments have not been reported in other orbiniids. The threadlike nature of these worms suggests that they are meiofaunal organisms.