A scidia mentula is a species of solitary tunicate it has a tough leathery envelope or tunic composed partly of cellulose. The translucent tunic encloses a fluid-filled body with irregular bulges and two inconspicuous siphons. It is 5 to 18 cm (2 to 7 in) tall, bottle or flask-shaped with the oral (inlet) siphon at the tip and the six-lobed atrial siphon half to two thirds of the way down.