Most modern groups of invertebrates

Most modern groups of invertebrates also appeared during the Triassic. A number of new orders of echinoderms (starfish, sea urchins and their relatives) evolve, although echinoids remain rare and of specialized types. Modern scleractinian corals appear, and in the equatorial Tethyean regions form small patch reefs no more than a meter high and often build on the decaying remains of sponge reefs. There are no massive reefs like those that exist today.
There are very little remains of phytoplanktonic. It is likely that the phytoplanktonic of the time were - soft-bodied forms, and hence they were not preserved as fossils.
Insects included many modern orders, as well as several extinct lineages. Little is known of other terrestrial groups of arthropods, but since they are known from both the Paleozoic and the later Mesozoic they must have been present.