Thecacera nudibranch feeding on bryozoa Caulibugula inermis

It is a bryozoan of the family Bugulidae with Indo-Pacific distribution.
Bryozoans in this family form erect, branched, unjointed and unilaminar colonies, attached by rhizoids. Zooids long, parallel-sided, with almost all of the frontal surface membranous; lateral walls lightly calcified; marginal spines usually present. Pedunculate “bird’s head” avicularia characteristically present. Ovicells independent and hyperstomial, with ectooecium membranous.