The Doliolida are an order of small marine animals of the subphylum Tunicata. They are in the class Thaliacea, which also includes the salps and pyrosomes. The doliolid body is small, typically 1–2 mm long, and barrel-shaped; it features two wide siphons, one at the front and the other at the back end, and eight or nine circular muscle strands reminiscent of barrel bands. The Doliolida have a complicated life cycle that includes sexual and asexual generations. They are nearly exclusively tropical animals, although a few species do occur as far to the north as northern California.