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. The polyps belong to a group of animals known as Cnidaria, which also includes sea anemones and jellyfish. Unlike sea anemones, corals secrete hard carbonate exoskeletons which support and protect the coral polyps. Reefs grow best in warm, shallow, clear, sunny and agitated waters. Often called 'rainforests of the sea', shallow coral reefs form some of the most diverse ecosystems on Earth. Cuttlefish are marine animals of the order Sepiida. They belong to the class Cephalopoda, which also includes squid, octopodes, and nautiluses. Cuttlefish have a unique internal shell, the cuttlebone. Despite their name, cuttlefish are not fish but mollusks. They have large, W-shaped pupils, eight arms, and two tentacles furnished with denticulated suckers, with which they secure their prey. They eat small mollusks, crabs, shrimp, fish, octopodes, worms, and other cuttlefish. Their predators include dolphins, sharks, fish, seals, seabirds, and other cuttlefish. The average life expectancy of a cuttlefish is about one to two years. Illustration by John George Wood (also known as Rev. J. G. Wood), 19th century. |