ABSTRACT
Epaulets are paired swimming organs that develop from the circum-oral ciliary band of echinoid larvae. In Paracentrotus lividus, the anterior epaulets arise in 6d larvae from band areas located between the lower lip and the post-oral arm of the larva and the posterior epaulets appear in 7d larvae from band areas located between the preoral lobe and the developing postero-dorsal arm. When they separate from the ciliary band, the epaulets simultaneously migrate towards the posterior part of the larval body and grow laterally until they form a nearly continuous ring perpendicular to the long axis of the body. Epaulets are ectodermic structures consisting of several rows of spindle-shaped cells underlined by a conspicuous nerve plexus. During the last week of larval life, the swimming of the plutei is only due to the ciliary beating of the epaulets that are also used as a rudder.
