-ēən noun
( -s )
Etymology: New Latin Ascidia (II) + English -an
: a simple or compound tunicate of the order Ascidiacea suggesting as a larva a minute active tadpole with an elongated tail that contains a distinct notochord and dorsal nerve chord showing obvious relationship to the vertebrates but as an adult lacking the tail and being reduced to a sessile saclike form with an anterior branchial opening through which water passes to a branchial sac having perforated walls which strain microscopic food into the digestive tract before the water emerges by way of an atrium and dorsal atrial opening ; broadly : tunicate