Sea turtles are reptiles of the order of Testudines. There are seven species of sea turtles. Four of the species have been identified as "endangered" or "critically endangered" with another two being classed as "vulnerable".
Sharks are a group of fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Evidence of the existence of sharks dates back to approximately 480 million years ago.
There are approximately 560 described species of skates and rays in thirteen families. They are in the fish subclass Elasmobranchii, along with sharks, to which they are closely related. Rays are distinguished by their flattened bodies, enlarged pectoral fins that are fused to the head, and gill slits that are placed on their ventral surfaces.
Osteichthyes, also called bony fish, are a taxonomic group of fish that have bone, as opposed to cartilaginous, skeletons. This gallery also portrays a few members of the phylum Cnidaria, commonly known as Jellyfish. Though these creatures aren't fish at all, being more closely related to coral polyps.
Coral reefs are diverse underwater ecosystems held together by calcium carbonate structures secreted by corals. Coral reefs are built by colonies of tiny animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups.