Sponges

These colorful sessile creatures are not plants! They are among the simplest multicellular organisms - do not have heads, eyes, brains, organs, and nervous system, yet they have been in the ocean for 500 million years. The phylum Porifera is named by the appearance of sponges. The body of sponges is a network of pores, canals, and passageways. They are the most primitive animal group that is still alive today.

Sponges have no mouth. Have you ever wonder how they eat without a mouth? Well, they are filter feeders, meaning they filter out the detritus, plankton, viruses, and bacteria in the water column as their food. Water is pumped into the holes of the sponges called ostia, then the water exits through larger openings called oscula. The sponges filter the water not only to obtain food, and at the same time purify the water.

The cells of the sponges are arranged around a skeleton of spicules, which is made of calcium carbonate, silica, and spongin (animal collagen) to maintain the sponge structure. The spicules are an important element to identify the sponge species, as the same species of sponges may exist in various kinds of external morphologies, such as color, shape, and pattern, but they still have the same spicules.

Similar to corals, sea anemones, and giant clams, the sponges have a symbiotic relationship with zooxanthellae. Besides these tiny little algae, sponges are homes for marine organisms such as sea snails, shrimps, fishes, and brittle stars. Can you believe a 2 meters tall sponges is a comfy shelter for 16, 000 shrimps? Sponges may synthesize toxic to prevent them to be eaten, yet there are still animals which chemically undefended to take sponges as their food, such as hawksbill turtles and nudibranchs.

Sponges are soft-body animals. How can they become reef builders? Coral reefs and sponges are known to thrive in poor-nutrition ocean areas because the symbiotic relationship with zooxanthellae forms the plant-based food chain. The sponges play biological roles on coral reefs such as harboring tremendous species of animal and plant symbionts and influencing ocean water chemistry.