Phylum Cnidaria General Information Cnidaria means a stinging

Phylum Cnidaria

General Information: • Cnidaria means ‘a stinging thread’ • Examples: sea anemones, corals, jellyfish, freshwater Hydra, and the Portuguese man of war • Habitat: marine and fresh water

Soft Coral Sea Anemone, Clover Point, Victoria B. C.

Portuguese Man Of War Brain Coral

Characteristics: Characteristics • All cnidarians have a basic radial symmetry and possess only 2 layers of living tissues. • 2 tissue layers: ectoderm and endoderm • Contain a mesoglea • Some possess an exoskeleton (for protection) made up of Ca. CO 3 (e. g. corals)

Characteristics • Have 2 body forms: a. Polyp (sessile) – e. g. hydra, coral, or sea anemone b. Medusa (free swimming) – bell shaped – e. g. jellyfish

• Some cnidarians contain only one body shape during their life cycle, while others contain both during their life cycle • When a cnidarian exhibits the 2 body forms in its life cycle, it is called polymorphism (‘many shapes’) • The evolution of a primitive nervous system sets these organisms apart from the sponges – called a nerve net • They contain nematocysts found on the tentacles used for capturing prey and for protection

• Mesoglea is sandwiched between ectoderm and endoderm • There amoebocytes in the mesoglea of cnidarians, much like in sponges • Cnidarians possess a simple digestive system – the gastrovascular cavity – where digestion and circulation of nutrients occur http: //shapeoflife. org/video/cnidarians life move

Sea Anemones – Class Anthozoa: • • No medusa stage They are all marine Polyp body form exclusively Reproduce asexually through longitudinal or transverse fission (like binary fission, but on a much larger scale) • Are primarily carnivorous – capture food using nematocyst studded tentacles and transfer it to a central mouth opening • There around 6000 species of sea anemones

Coral – Class Anthozoa • Colonial form of Class Anthozoa • Can have soft and hard corals • Hard corals secrete external Ca. CO 3 skeletons and are called ‘stony corals’ • Stony corals make up coral reefs (not all make reefs though) • Coral add about 10 kg of additional Ca. CO 3 per m 2 of reef yearly • Soft corals do not have hard external skeletons

The Anatomy of A Coral • Many corals have symbiotic green algae called zooxanthellae living in their polyps • Warmer ocean temperatures can cause these algae to die, resulting in a phenomenon known as “coral bleaching”

Corals are an important part of BC marine ecosystems! • In BC, deep water corals such as the red tree or “Gorgonian coral” provide shelter for juvenile rockfish such as the yelloweye rockfish or sharpchin rockfish

Jelly Fish – Class Scyphozoa • Only a few hundred species – nearly all are marine • The body is in the form of an inverted cup, with nematocyst studded tentacles extending downward from the cup. • Some jellyfish have symbiotic unicellular algae that give them nutrients • The life cycle of jelly fish involves the two different body forms: polyp and medusa

A Typical Jellyfish Life Cycle

A Typical Cnidarian – Hydra Class Hydrozoa Structure: • Polyp body form Locomotion: • Sessile; however, some can somersault and glide along while secreting mucus

Ingestion, Digestion, Elimination • Food is captured by nematocysts in the tentacles by stinging or stunning prey • Tentacles push food through mouth into gastrovascular cavity • Flagella line the endoderm layer and create a current • The endoderm cells secrete enzymes to break down food • Food is taken into cells and nutrients are circulated by amoeboid cells • Wastes are eliminated out through the mouth • https: //www. youtube. com/watch? v=Kukv 0 At. IVd

Respiration • O 2 enters the cells by diffusion • CO 2 leaves the cells by diffusion

Nervous System • Have a nerve net within the mesoglea • When stimulated, the nerve net will respond by contracting / relaxing the muscles • Have sensory cells that are sensitive to touch, light, chemicals, and balance

Muscular System • Longitudinal and circular muscle fibres are found in the endo / ectoderm layers

Excretion • Nitrogenous wastes leave the cells by diffusion • Solid wastes enter the gastrovasuclar cavity and leave via the mouth (Elimination)

Reproductive System A. Asexual • Budding (bud breaks away) • Regeneration (re growth of missing parts) A Hydra Budding

Reproductive System B. Sexual • Some are hermaphrodites • Ovaries and testes grow on the side of adults • Ovary produces an egg and remains attached to the adult • Testes produce the sperm which swim to the egg, resulting in a zygote • Zygote develops into a ball of cells called the blastula, which develops into a ciliated larva called a planula, planula which can swim to another location, settle, and develop into a polyp adult

Evolutionary Significance • Cnidarians are the first animals to have organized true cell tissues • They are therefore the first true multicellular organisms to appear • They are the first organisms to have muscle tissue and nervous tissue • Cnidarians, having radial symmetry are thought to share a common ancestor with all other multicellular animals