The key is mostly dichotomous but sometimes polytomous. For most alternatives (couplet questions) there is a picture (photo or drawing) illustrating the features in question. In some cases, the same genus appears in more than one location in the key. The reason is the large ecophenotypic variation among many species.
When the key has guided you to a genus name, there are two options:
One is a link to the webpage for the genus in the database WoRMS (www.marinespecies.org).
The other option is to click on the image icon of the genus. Clicking on it results in a series of photos of species belonging to that genus.
For identification below the genus level, to species, users are recommended to use the species list in WoRMS (www.marinespecies.org) combined with other sources (handbooks, scientific literature, reliable webpages etc). Identification to species can be very difficult or uncertain because of the enormous ecophenotypic variation, hybridization, growth of chimaeras etc.