Microrbinia Hartman, 1965

Blake, James A., Ravara, Ascensão & Bongiorni, Lucia, 2025, Two new species of Orbiniidae (Annelida, Polychaeta) from the Condor Seamount, Azores, NE Atlantic Ocean, Zootaxa 5686 (3), pp. 393-405 : 400

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 with one or two asetigerous rings. Noto- and neuropodia with welldeveloped postsetal lobes; branchiae absent; parapodia lateral to dorsolateral, some notopodia directed dorsally, but not shifted onto dorsal surface in abdominal segments. Branchiae absent. Setae include crenulated capillaries throughout; posterior notosetae include acicular spines; neuropodia with acicular spines present or absent; furcate and flail setae absent. Pygidium with 2–4 anal cirri. Males with a conical gland-like dorsal organ on a few abdominal segments.

Remarks.: The genus Microrbinia is currently known only from the type-species, M. linea from the U.S. Atlantic continental slope (600–3015 m) ( Hartman 1965; Blake 1993, 1994, 2021). The species is unusual among orbiniids in having a conical gland-like structure on the dorsal surface of some anterior abdominal segments ( Blake 1993; 2021). These structures 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. Microrbinia linea has unusual serrated notopodial acicular spines in middle and posterior abdominal segments that have not been reported in other orbiniids. Another species has been found among the orbiniids collected from the Condor seamount and has several characters that required the definition of the genus to be emended. The new species has two peristomial rings instead of one, two anal cirri instead of four, and the acicular spines occur in both noto- and neuropodia instead of only notopodia and are smooth instead of serrated.