A sponge is full of holes but still holds water. Sponges are the simplest of multicellular animals and are found on the ocean floor.
Sponges are from the primitive, multi-cellular animals under the phylum of porifera. Porifera translates to "pore bearing" as they are the ostia that covers their exterior. There are approximately 5,000 discovered species with habitats in bodies of water. Sponges attach themselves to surfaces on the ocean floor and some species can survive up to 28,000 feet below sea level.
The sponge's anatomy lends itself to filter feeding with flagella beating water, nutrients and bacteria through the sponge's spongin. Spongin is a mesh of protein used to capture nutritious bacteria and particles. Sponges are hermaphroditic, but produce only one type of gamete during their spawn. All sponges are capable of playing both roles, but use one each spawn. The male releases sperm that is absorbed by the female. Internal fertilization and gestation occur until planktonic larvae are released by the female. After a few days, the larvae settle on the ocean floor and begin to grow.
Sponges are split into two types, encrusting and free standing. Encrusting sponges cover rocks like a moss and maintain their shape. Free-standing sponges are more versatile and have a greater inner volume compared to their outside surface area. Free-standing sponges grow into varying shapes and sizes.