Yellow ascidian

Scientific name : Ascidia sp. 4

Different specioes of ascidians are living into crevices, on the underside of corals, with siphons popping out. Some have siphons with a distinctive coloration, like this yellow-translucent species.
Living on the reef front and along the external reef, in crevices and under corals.
Similar to a Phallusia sp.