Author: John Turnbull
Identifying fish is easy! You start to think that when you try to identify sessile organisms like sponges, ascidians and bryozoans. To identify these correctly often requires a sample and a microscope, as it’s the shape of the tiny structures inside that tell you the species.
Sponges have the additional complication that their shape and form can change as they grow, and according to environmental factors like currents. An encrusting sponge can grow upwards into a massive form, and a given species will look different in strong currents vs weak.
So instead of trying to identify to the species level, we can identify based on shape or morphology. In recent work by scientists, most notably Christine Schoenberg in WA, sponges are being classified into categories according to shape. These include:
Each category is then subdivided, for example erect shapes include laminar (flat), palmate (hand-like), branching and stalked. The "cheat sheet" is here.