'ascidian' originates from Modern Latin 'Ascidiacea', ultimately from Greek 'askidion', where 'askos' meant 'bag'.

'askidion' (Greek) changed into Latin/Medieval forms such as 'ascidia' and New Latin 'Ascidiacea', and eventually became the modern English word 'ascidian'.

Initially it meant 'little bag' (referring to the saclike shape); over time it came to refer specifically to the group of sea-squirts (tunicates) known as ascidians.