Cupular sense organs in Ciona (Tunicata: Ascidiacea)

TLDR

Ciona is sensitive to near‑field vibrations even after brain removal. The study discusses the significance of this observation and the arrangement of the cupular organs. The cupular organs of Ciona’s atrial siphon resemble vertebrate acoustico‑lateralis structures, with ciliated sensory cells and supporting cells secreting a polysaccharide‑protein cupula, indicating that tunicates provide a suitable morphological starting point for the vertebrate system.

Abstract

The cupular organs of the atrial (exhalent) siphon of Ciona have been studied with scanning and transmission microscopy and are shown to resemble those of the vertebrate acoustico‐lateralis system in several respects. The sensory cells are ciliated, and their cilia are apparently non‐motile, having a modified inner tubular array. These cells lie amongst supporting cells that probably secrete the cupula, which is composed of polysaccharide and proteins as is the test. Ciona is sensitive to near‐field vibrations, even after the brain has been removed; the significance of this observation and of the arrangement of the cupular organs is discussed. It is concluded that the tunicates show a suitable morphological starting point for the vertebrate acoustico‐lateralis system.