Hydroids and hydromedusae are abundant and widespread, but they can be difficult to identify, in part due to the overwhelming amount of terminology used to describe their polyps, colonies and medusae. The diversity of shapes and life cycle strategies in Hydrozoa is in fact so high that it is almost impossible to find a single set of descriptive terms for all species, and different glossaries have been developed for closely related families, sometimes genera, and also for the different stages in the life cycle of the same organism. To further complicate things, the terminology we use for the characterization of hydrozoan morphology has been adapted in many cases from other fields of science (like botany and geometry), and some of the words ended up with very different meanings depending of the organism we are looking at.
But if you are interested in these fascinating creatures, fear not! We at the invertebrate collections have thought about giving you a little visual aid in the form of four plates including some of the basic structures of hydroids and hydromedusa (courtesy of artsprosjekt HYPNO and upcoming artsprosjekt NORHYDRO).
Hopefully these images can be used as a starting point for the uninitiated, and why not? perhaps also as a source of inspiration for cool marine-related presents for the season!
-Luis Martell and Joan J. Soto Àngel