Ultrastructure of the organ of Bellonci in the hypogean isopod Stenasellus virei boui Magniez (Crustacea, Asellota)

Abstract

The ultrastructure of the organ of Bellonci in the hypogean isopod Stenasellus virei boui was investigated. There are two organs located anterodorsally, one on each side of the cephalon. Each organ consists of a wall surrounding a cavity with a central core irregular in shape. The bordering wall contains some glial cells and the inner dendritic segments of 25–28 sensory cells, each one bearing two cilia. Each cilium has a typical 9 + 0 axoneme, a basal body, and a long straight ciliary root that is at a right angle to the basal body; the cilium branches out into tubules that usually contain 1 microtubule, occasionally 2 or more. The ciliary tubules are gathered in three or four long bundles and are not linked to the core. The ciliary connections appear to be both conical and cylindrical. The ultrastructural morphology (polarization of the cilia, spatial arrangement of the bundles and central core) suggests that this organ can record directional stimuli.