Habitat
A. ephippium is found primarily in sheltered conditions in the low intertidal and sublittoral zones. They are a benthic species that lives in depths from 25-200m. They are distributed along coasts around the world. They are found on the South and West coasts of Britain, stretching North to Shetland and are also found on all coasts of Ireland. They are also found along the Atlantic Coasts of the United States ranging from Massachusetts to Florida. Specifically within the Massachusetts region, they have commonly been found in the Woods Hole region.

