Cnidaria Greek word Cnidos meaning stinging nettles Phylum Cnidaria Greek word Cnidos meaning stinging nettles

Cnidarians Their development make it possible for these organisms to: Swim Respond to external stimuli Engulf prey

Symmetry of Cnidarians Cnidarians display Radial Symmetry. similar parts of the body are arranged and repeated around a central axis Cephalization – the differentiation of the anterior end of an organism into a definite head (their bodies are not divided into distinct head and trunk) Examples: Jellyfish Corals Hydra Sea anemones

Medusoid Jellyfish

Sea Anemones

Coral

Hydra

Portuguese Man-O-War

Structure of Cnidarians Oral surface Aboral surface Centrally located mouth Tentacles Cnidarians have two basic forms: polyp – a sac-like attached stage with the mouth and tentacles oriented upward Medusa – bell-like, which is like an upside down polyp adapted for swimming

Parts of Cnidarians Mouth Gastrovascular cavity Epidermis – outer layer Gastrodermis – inner layer of cells lining the gastrovascular cavity Mesoglea – ranges from a non-cellular, thin membrane to thick jelly-like material between the epidermis and gastrodermis

Classes of Cnidarians Hydrozoans Scyphozoans Anthozoans Freshwater hydra Portuguese Man-O-War Some coral such as fire coral Cubozoans Box jellyfish Scyphozoans Jellyfish Anthozoans Sea anemones Coral

Feeding & Digestion of Cnidarians Most all are Carnivores Use Nematocysts to capture prey The stinging cells are called cnidocytes Two phases of digestion: Extracellular Intracellular

BEHAVIOR OF Cnidarians Cnidarians lack a brain or true nerves. They do, however, have specialized nerve cells Nerve cells interconnect to form Nerve Net. Cnidarians are diploblasts – they have two germ layers

Economical Importance Cnidarians have little economical importance, however reef-building corals are an exception. Fish and animals associated with reefs provide substantial amounts of food for humans Some Asian countries consume jellyfish as a delicacy.

Comb Jellies Phylum Ctenophora Resemble that of medusa Have radial symmetry Has a gelatinous body that resembles a medusa Differences they only have two long tentacles but have comb structures and lack stinging cells.

Comb Jelly (Ctenophora)