PHYLUM 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 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: � 1. 2. 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

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

Classes of Cnidarians � Hydrozoans �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: 1. Extracellular 2. Intracellular �

BEHAVIOR OF 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)