Many of the 6,000 known species of red algae (rhodophytes, from the Greek rhodos, red) are reddish, owing to a photosynthetic accessory pigment called phycoerythrin, which masks the green of chlorophyll. However, species adapted to more shallow water have less phycoerythrin. As a result, red algal species may be greenish red in very shallow water, bright red at moderate depths, and almost black in deep water. Some species lack pigmentation altogether and function heterotrophically as parasites on other red algae. Red algae are the most abundant large algae in the warm coastal waters of tropical oceans. Their accessory pigments allow them to absorb blue and green light, which penetrate relatively far into the water. A species of red alga has been discovered living near the Bahamas at a depth of more than 260m.