Cliona viridis, commonly called the green boring sponge, is a species of demosponge in the family Clionaidae. Its form varies according to the nature of the surface on which it grows. In limestone and other calcareous substrates it excavates channels and chambers while on other types of rock it encrusts the surface or forms massive structures. It is native to the eastern Atlantic, the Mediterranean Sea and the Indo-Pacific Ocean.

Description Cliona viridis is an excavating sponge and on calcareous substrates, the mass of the sponge is largely unseen beneath the surface with just the osculi (exhalent openings) and ostioles (inhalent pores) projecting. The osculi are a few millimetres wide and are yellowish-green or light brown with pale rims. The ostioles are grouped together on flat-topped, sieve-like protuberances which may be white, yellow or brownish-green. The colour is due to the zooxanthellae which are present in the tissues. The exterior appearance of this sponge in its later growth stages is a smooth mosaic-like surface composed of a firm, tough material. Beneath this surface are galleries excavated by the sponge which are up to 2.5 mm (0.1 in) in diameter.