Tunicates can be found in a variety of colorationsAmong the more fascinating creatures that commonly make their way into marine aquariums as stowaways on good-quality live rock are tunicates, or sea squirts. In terms of visual interest, these animals can be quite dazzling, with some exhibiting spectacular coloration or resembling small, delicate, translucent pitchers or urns. What are they? Tunicates are filter-feeding marine organisms with a very simple body plan. Essentially, they’re water-filled sacks with two openings—an incurrent (or oral) siphon and an excurrent (or atrial) siphon. As you’ve probably deduced already, sea water is drawn into the animal through the incurrent siphon, tiny planktonic particles are filtered out, and then the water is expelled through the excurrent siphon. These creatures can be either solitary or colonial and are often mistaken for sponges.
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