Hydrozoan colony and amphipods. Amphipod (Stenothoe marina) crustaceans sheltering amongst the tentacled feeding structures of a hydrozoan (Tubularia larynx) colony. Hydrozoa are a type of cnidarian and are related to corals and sea anemones. Amphipods are small crustaceans that typically have a laterally flattened body and fourteen limbs. They form part of the zooplankton