Echinoderms have been used often as experimental models in developmental biology and evolutionary biology studies. Numerous data on echinoid and asteroid development are available, whereas little is known about crinoid larval biology. This contribution focussed on the life cycle of the Mediterranean feather star Antedon mediterranea. Light and electron microscopy were used to characterize, in detail, the morphology and behaviour of the main larval stages. Similarities and differences with respect to what is already known for other crinoids, and echinoderm species, were explored. In view of the importance of serotonin during settlement and morphogenesis, analyses of the distribution of this molecule were carried out on swimming larvae. Immunolabelling results suggested a role for serotonin in A. mediterranea development, underlining the ancestral importance of this conserved neurotransmitter in deuterostome evolution.