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Guide to New Zealand's freshwater invertebrates
Hydrozoans (Phylum Cnidaria) are small, predatory animals, most of which are marine, but a few live in fresh water. Cordylophora is a colonial genus with many small anemone-like animals at the ends of branching stalks. At first glance the colony looks like a brown moss or a bryozoan colony.
Cordylophora is rarely recorded in New Zealand freshwaters. Our only specimens came from a muddy site in the lower Waipori River in Otago, where there was some tidal influence.
They use stinging tentacles to capture small invertebrate prey.
The site where we found Cordylophora is more influenced by tidal influence (including some salinity) than other aspects of water quality. No tolerance values have been assigned to this genus, but the nearest relative with tolerance values is Hydra with values of 3 (hard bottom sites) and 1.6 (soft bottom sites).