Communication and Perception
All hydrozoans have tactile and chemical sensing structures. Some also have eyespots that detect light, and/or statocysts that detect gravity. They communicate mainly by chemical signals. Some free-swimming hydrozoans, including many siphonophores have bioluminescent structures. It's not known what function these serve. It is unlikely that they communicate with other hydrozoans (their light sensors are too simple for this). Possibly they are lures for prey or have some predator defense function.
Communication Channels: visual ; chemical
Other Communication Modes: photic/bioluminescent ; pheromones
Perception Channels: visual ; tactile ; chemical