Up for sale are brown tube sponges. Sponges are simple multicellular animals that sessile filter feeders. Sea sponges do not have a digestive, nervous, or circulatory systems but rely on the constant flow of water to obtain food and oxygen and to remove wastes by the beating of flagella by the collar cells of the organism. These tube sponges would be great for beach or ocean decor or for collectors of strange and unique curiosities.