Critter of the week: Ophiactis abyssicola
Ophiactis abyssicola (Sars, 1861) is a very common deep sea species of brittlestar distributed throughout New Zealand waters and in temperate regions in the Pacific, Indian, and Atlantic Oceans.
It lives on sponges, inside dead snail shells, and in the matrices and crevices of live deep sea branching corals like Solenosmilia variabilis Duncan, 1873 up off the seafloor from where they filter-feed by extending their mucus covered arms into the water column (Pearson & Gage, 1984). These types of habitats, and hence this species, are commonly found on seamounts and knolls.
In the NIWA Invertebrate Collection we have records of specimens that look morphologically like Ophiactis abyssicola at depths from 378–2675 m but recent genetic research has shown that the sub species known as Ophiactis abyssicola cuspidata Lyman, 1879 found widely distributed from SE Australia, throughout New Zealand and down to the sub-Antarctic Macquarie Ridge region is only found from 174-1801 m (O’Hara et al., 2014). Our deeper records might well be the closely related species Ophiactis amator Koehler, 1922 found from 1142–2640 m deep (O’Hara et al., 2014).
For budding taxonomists of the brittlestars, this is a really easy species to identify in deep sea samples from seamounts, and you can find a diagnosis here from ophiuroid expert Dr. Tim O’Hara at the Museum of Victoria.