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Sponges are notoriously difficult to identify. Colors vary and even the shape or size of a sponge does not necessarily mark its species; sometimes shape is just a response to local conditions. Scientists would call this new form an "ecomorph."

Scientists rely on detailed examination of the internal "skeleton" to identify sponges. Sponges are made of a proteinaceous secretion called spongin. This fibrous net forms the useful part of the bath sponges (Spongia and Hippospongia) harvested in the Mediterranean and Caribbean. Many sponges also contain spicules of silica or calcium carbonate, or both, bound together with spongin.

There are an estimated 830 species of sponges in Indonesia. The giant barrel sponges are most impressive to divers, but the smaller tube sponges and vase sponges also create colorful and aesthetically pleasing forms.

Marine dinoflagellate plankters, top to bottom: Gymnodinium, Gonyaulax, Peridinium, Ceratium.

Like many invertebrates, sponges can grow to a remarkable age. Experiments with commercial farming of bath sponges in the Caribbean have led researchers to estimate that larger specimens are at least 50 years old, and maybe much older.