Image (Pallas, 1771)

Cordylophora is a small invertebrate animal related to corals, sea anemones, and jellyfish (Phylum Cnidaria, Class Hydrozoa). Known originally from the Caspian and Black Seas, its range has been expanding globally since the early 20th Century, probably from boat traffic and the commercial trade of aquatic plants. It occurs in fresh and brackish water feeding on chironomid larvae, zooplankton, and other small invertebrates.

Like many bryozoans, Cordylophora grows as a colony with branching tubules attached to submerged surfaces and has a moss-like appearance. Free branches also are formed under certain conditions. Repeating units of the colony, called polyps or hydranths, grow erect from the substratum and measure about 1 mm long. Each bears a cluster of 10-20 thinly scattered tentacles at its tip capable of capturing and paralyzing microscopic prey. Unlike bryozoans, the tentacles of Cordylophora can be shortened but never withdrawn into a protective tubule.

With the onset of unfavorable conditions, such as cold temperatures or limited food, polyps lose their tentacles and the living tissue withdraws into basal tubules. Small portions of the colony, called metanonts, become dormant and capable of surviving freezing temperatures, low oxygen, desiccation, and other extreme conditions. Details of this dormancy and the tolerance of metanonts to environmental stress have not been clarified.

Sexual reproduction involves the production of gametes by male and female polyps. A cluster of 6-12 eggs is retained by the female. Shortly after fertilization, eggs develop into ciliated, nonfeeding larvae which carried off by water currents to establish new colonies elsewhere.