LeslieH
Contributor
I'd go with tunicate. There's a picture of something very similar in Gosliner, Behrens, & Williams' book "coral reef animals of the Indo-Pacific. Listed simply as Didemnid sp (meaning it's in the family Didemnidae but not identified any further than that) all the book says is "This strange didemnid tunicate is composed of an encrusting mass with stringy lobes. Color greyish-white. This species has been found on the ceilings of caves and overhangs."