Abstract
The euopisthobranchs constitute a taxon of marine gastropods with around 1000 described species. This taxon has a worldwide distribution, from tropical to polar seas, ranging in habitats from intertidal to the deep marine ecosystems. The euopisthobranchs present a large morphological diversity. In some species the shell is external, but there is a strong tendency to shell reduction and internalization. Hence, they range from the limpet‐like Umbraculida and bubble‐shelled cephalaspideans to a variety of sea slugs, including the sea hares (Anaspidea). The Euopisthobranchia comprise both herbivores and carnivores. Most are benthonic, but the pteropods are pelagic swimmers.