Phylum Cnidaria Class Anthozoa By Richard and Tony
Phylum CnidariaIncludes organisms such as jellyfish, hydra, sea anemones, and corals.Are radially symmetric.Have two basic body forms, Medusae and Polyp.Have complex life cycles with asexual polyp stages and sexual medusae stages.Organisms in phylum Cnidaria also have colonial forms.
Characteristics of Corals Are colonies of tiny polyps which reproduce both asexually and sexually. Have a colonial form that allows for sharing of nutrients Can produce exoskeletons to protect against predators. Do not form medusa unlike other Cnidarians.
Types of CoralsHard corals (hermatypic): secrete a limestone exoskeleton around itself as protection. The exoskeleton or shell of the coral remains even after the organism dies.Soft corals (ahermatypic): are tree-like and flexible with a skeleton within their bodies giving them shape but allowing movement with the waves
Life History Corals first appeared during the Cambrian period, 542 million years ago Didn’t build reefs but existed as small solitary organisms During the Ordovician period 488 million years ago, tabulate corals become widespread Corals were very abundant. Like modern corals, these ancestors built reefs, some of which ended as structures in sedimentary rocks A coral reef exoskeleton found in the Coloured Canyon in Sinai, Egypt.
Reproduction Corals reproduce either asexually by budding or by sexually releasing gametes (sperm and eggs). Asexually, budding occurs when a new zygote grows onto another one and remains attached, separating only when mature. Sexually, fertilization can occur within a coral known as “brooding” or outside of a coral known as “broadcasting”
Life Cycle For brooders, internal fertilization occurs with gametes within the coral For broadcasters, fertilization occurs outside of the coral The zygote formed then enters the stage as a free- swimming larva until it matures and becomes a polyp Once it becomes a polyp it remains rooted and when matured, releases gametes
Consumption Polyps feed on organisms from microscopic plankton to small fish. Polyps release nematocysts from their calices to stun and kill their prey
Habitat and NicheCorals are found in all oceans from tropical to polarregions, but coral reefs are formed mostly in tropicaloceans near the equator. Coral reefs, which are consolidated limestone coral,provide shelter, spawning, nursery, and feeding area formarine organisms. They even act as physical barriers toprotect the shores from waves.