Until very recently, no evidence had been found for the existence of a hydroid stage, and it was generally considered that development must proceed from the egg through some larval form direct ...

How many species of jellyfish are there? Jellyfish are sometimes called sea jellies. They belong to a group called Medusozoa which is divided into four classes: Hydrozoa, Scyphozoa, Cubozoa and ...

told BBC News NI they are "quite different from the usual jellyfish you might find stranded on beaches". "These small, oval-shaped organisms, about 5-8cm long, belong to a group called Hydrozoa ...