Is this a Tunicate?

[GoReefin]

Came in as a hitchhiker

 

[ISpeakForTheSeas]

Yeah, that's a solitary tunicate - neat and harmless filter-feeder:

If you want to try and help the tunicates do well, offering some phytoplankton would probably be wise. Isochrysis and Rhodomonas or a blend containing at least one of these would be my first choice. For a more intensive diet that would likely show better results, see "Table 3" in the link below:

Coupling feeding activity, growth rates and molecular data shows dietetic needs of Ciona robusta (Ascidiacea, Phlebobranchia) in automatic culture plants - PMC

The sea squirt Ciona robusta is a model organism characterized by a transparent body, exhibiting peculiar physiologic and evolutionary characters. In vitro fertilization and breeding of sea squirts is possible, in order to preserve consistent ...

www.ncbi.nlm.nih.gov