Phylum Cnidaria

Hydra, jellyfish, coral, & sea Hydra, jellyfish, coral, & sea anemonesanemones

•Both phyla Cnidaria and Both phyla Cnidaria and Ctenophora make up the Ctenophora make up the radiate animals. radiate animals.

•They don’t have They don’t have advanced beyond tissue advanced beyond tissue level of organizationlevel of organization although a few organs although a few organs are seen. are seen.

•No respiratory or No respiratory or excretory system.excretory system.

–They have an They have an internal body cavity: the internal body cavity: the gastrovascular gastrovascular cavitycavity in which extracellular digestion occurs. in which extracellular digestion occurs.

–The cavity has The cavity has a single opening a single opening (it’s both mouth and (it’s both mouth and anus)anus)

–TentaclesTentacles around the opening. around the opening.

Special Special stinging cellsstinging cells (cnidocytes) that contain (cnidocytes) that contain a specialized stinging organelle, the a specialized stinging organelle, the nematocystnematocyst are are abundant on tentaclesabundant on tentacles. . Coiled thread discharges like a harpoon. It Coiled thread discharges like a harpoon. It contains neurotoxin that paralyze preyscontains neurotoxin that paralyze preys

– The simplest animals with nerve cells; The simplest animals with nerve cells; there is no central nervous system. there is no central nervous system.

– The simplest animals with sense The simplest animals with sense organs (statocysts –balance- and ocelli organs (statocysts –balance- and ocelli –eyespots-)–eyespots-)

–They move with the water currents or They move with the water currents or by contracting their bodyby contracting their body..

–Two typesTwo types according to their body according to their body shape: shape:

–Polips (cylindrical and attached to Polips (cylindrical and attached to floor)floor)

–Medusae. (umbrella-shaped, Medusae. (umbrella-shaped, gelatinous and free-swimming)gelatinous and free-swimming)

- Sea anemones and corals are all polyps with no medusa stage.- Some have an exoskeleton or endoskeleton of chitinous, calcareous or protein components.

•Cnidaria Cnidaria

– All are aquatic and mostly marine. All are aquatic and mostly marine.

– Radial symmetry. Radial symmetry.

– Reproduction is either asexual or sexual; a Reproduction is either asexual or sexual; a planula larva may be present.planula larva may be present.

Class Hydrozoa Class Hydrozoa

–HydraHydra are solitary polyps and are solitary polyps and one of a few cnidarians found in one of a few cnidarians found in freshwater. freshwater.

Class AnthozoaClass Anthozoa

• 1. 1. Sea AnemonesSea Anemones

– a. They attach to shells, rocks, wood, etc.; some a. They attach to shells, rocks, wood, etc.; some burrow in mud or sand. burrow in mud or sand.

–Some have a mutualistic relationship with hermit Some have a mutualistic relationship with hermit crabs. crabs.

Clown fish with sea anemone

Class Anthozoa Class Anthozoa

• 2. Corals 2. Corals

– They are miniature sea anemones that live in They are miniature sea anemones that live in calcareous cups they have secreted.calcareous cups they have secreted.

– Hermatypic corals and coralline algae form most Hermatypic corals and coralline algae form most coral reefs. These corals require full salinity of coral reefs. These corals require full salinity of seawater and warmth and light, limiting them to seawater and warmth and light, limiting them to waters between 30 degrees north and south. waters between 30 degrees north and south.

Class Scyphozoa: True Jellyfish

Fried egg jelly

Jellyfish