The Echinarachniidae are found from Eocene deposits to the present day. There are a number of recognized genera: Faassia (Miocene Kamchatka), Proescutella (Eocene France), Pseudastrodapsis (Miocene-Pliocene Japan and Kamchatka), Astrodapsis (Miocene-Pliocene California to Baja California), Echinarachnius (Miocene-Recent), Scutellaster (Oligocene-Pleistocene Pacific Coast of North America), and Vaquerosella (Miocene California and Baja California) (Squires and Demetrion 1993; Martinez-Melo and Alvarado-Ortega 2020). The tiny sand dollar Kewia (see, for example, Wagner 1974, Linder et al. 1988) is sometimes synonymized with Scutellaster (e.g. Smith and Kroh 2011), but not always (Kroh and Mooi 2021). There is likely a need to re-evaluate the family. The Pliocene genus Remondella is sometimes included within the Echinarachniidae (Beadle 1991).
Echinarachnius parma, the northern sand dollar, is the only living species of the family. It is native to the oceans of the Northern Hemisphere. In the U.S., it is most common on the northern East Coast to the Maritimes, and along the coastline of the Pacific Northwest up to Alaska and the Aleutians.
