For 20-gallon tank
1 Sea anemone (Condylactus, Calliactis, Bunodactis, Ceriantheopsis, species as available).
1 Starfish (Echinaster/ Luidia/ Astropecten)
2 Brittlestars (Ophioderma)
2 Sea urchins (Arbacia/ Lytechinus)
1 Colorful and hardy sponge (Axinella/ Xestospongia/ Cliona)
1 Sea whip (Leptogorgia)
2 Living shells or rocks (Chitons/ Feather Duster Worms/ Serpulids/ Boring Sponges/ etc.)
2 Hermit crabs (Clibanarius/ Pagurus)
2 Snails (Cantharus/ Nassarius)
1 Algae
1 Sea Cucumber (Pentacta/ Thyonella)