These are found in the Phylum Porifera, and there are four classes, 5 subclasses, 28 orders, 232 families, and 977 valid genera, and probably over 15,000 species. Most are found in marine waters, and vary in size, shape, and color. Porifera means 'pore-bearer,' and these animals are sessile filter feeders usually found attached to hard surfaces and they are the simplest of multicellular creatures.
Even though there appears to be four Classes of Sponges, (Demospongiae; Calcarea; Hexactinellida; and, Archaeocyatha) only two, Demospongiae and Calcarea have those containing anything that might even remotely be of interest to aquarists having tropical or temperate aquaria. Yet the taxonomy labels relating to these creatures in these classes of interest contain 'numerous' subdivisions/subtitles that would overly complicate their display here. Therefore, to facilitate finding species of interest I'll simply divide this subject matter into four categories;
(1) Those appearing in the trade on purpose and having some value in our aquariums - General Aquarium Sponges
(2) Those that may arrive as hitchhikers on corals or live rock and rarely survive - Hitchhiker Sponges
(3) Those seen in tropical areas in the wild and should remain there - Best Left in the Wild Sponges
(4) Those that are cool water species possibly having value for temperate aquariums or should simply remain in the wild in their locations - Cool Water Sponges
In each category their scientific names will be listed in alphabetical order within their families, followed by their common name. Each description will also contain its taxonomy should that be of interest. This way, you can cut to the chase so to speak if wanting to find information on a sponge normally seen in the trade, or one that may be a hitchhiker on some piece of live rock or coral. Then again, if temperate systems are of interest, then go directly to those cool water species. Otherwise, maybe you just want to ID some interesting sponges seen while diving or those that 'should' be left in the wild, if so then go to that category. Hopefully, this division of interesting sponges will be helpful. And if there are changes that you would like to see, just contact me and we can go from there.
I've also tried to up-to-date this phylum, which may be the first time any hobbyist has made such an attempt! In doing so, John N. A. Hooper's 'Sponguide: Guide To Sponge Collection And Identification' was quite helpful as to their taxonomy aspects.
Please click on the Sponges group you are interested in viewing.