Scuba diving in Belize, off Placencia.
Gorgonians (Sea Fans, Sea Whips) are sessile colonial animals belonging to the order Gorgonacea in the class Anthozoa. They might look like plants, but they are actually animals belonging to the same subclass as soft corals, sea anemones and sea pens/ sea pansies (Alcyonaria). A central internal skeleton, composed of a flexible, horny substance called gorgonin, supports all branches of the colony, and the living tissues form a layer over its entire surface. The polyps spread out their tentacles to form a plankton-catching net. In most cases the fan-shaped colonies grow across the current, which increases their ability to ensnare prey. Sponges are the primitive multicellular aquatic animals that constitute the phylum Porifera. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through them, consisting of jelly-like mesohyl sandwiched between two thin layers of cells. Many sponges have internal skeletons of spongin and/or spicules of calcium carbonate or silica. They can have various shapes, sizes, and colors. Sponges do not have nervous, digestive or circulatory systems. Instead, most rely on maintaining a constant water flow through their bodies to obtain food and oxygen and to remove wastes. Without sponges, many species of fish and aquatic animals would lack food and shelter and reefs would be significantly less diverse.