Pyrosoma is a genus of colonial, pelagic (open-ocean) tunicates. Colony size ranges from less than a centimeter to several meters in length. Each colony forms a transparent tube, closed at one end and open at the other, that is composed of hundreds or even thousands of outward-facing individuals (or zooids). These tiny zooids, each just millimeters long, are joined together by a gelatinous tunic. Water is drawn into each zooid through an oral siphon by beating cilia, creating a feeding current. Plankton are filtered out of the water and the depleted water is then expelled into the interior of the colony and out the posterior opening. This flow of water not only facilitates food acquisition, but also allows the colony to move by graceful jet propulsion, although Pyrosoma are mainly planktonic (passively free-floating).
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