Suctoria

Suctoria are ciliates which become sessile in their developed stage and then lose their redundant cilia. They feed by extracellular digestion. They were originally thought to feed by suction – hence their name. In fact, they use specialized microtubules to ensnare and manipulate their prey. They are found in both freshwater and marine environments, including some which live on the surface of aquatic animals, and typically feed on other ciliates. Instead of a single cytostome, each cell feeds by means of several specialized tentacles. These are supported by microtubules and phyllae, and have toxic extrusomes called haptocysts at the tip which attach to prey. Its cytoplasm is then sucked directly into a food vacuole inside the cell, where its contents are digested and absorbed. Most suctoria are around 15-30 μm in size, with a non-contractile stalk and often a lorica or shell.