sponge
i think its alright to leave sponge in the sand. n they don't require intense light. however, it do need strong water flow.. as sponge get their food by filtering the water through its body. orange colour sponge should be fine, it strive better in the aquarium than the blue or purple one.. another thing, sponge do not like to be lift up above the water and get into contact with air.. their colour will fade and die slowly.. better watch out!