Lithocytes are transported along the ciliary surface to build the statolith of ctenophores

All organisms capable of locomotion possess equilibrium receptor systems that use the gravitational field as a reference. In aquatic invertebrates, gravity receptors (statocysts) are considered to be the earliest known sense organs. Statocysts are composed of a dense mass (statolith or statoconia) that loads and mechanically stimulates sensory receptors, which are commonly cilia. Ctenophores, or comb jellies, are gelatinous marine zooplankton with eight meridional rows of locomotory ciliary comb plates [1,2]. Their aboral statocyst contains a single massive statolith, which consists of numerous living cells (lithocytes), each with a nucleus and a large membrane-bound concretion [1,3]. Correspondences