Phylum Cnidaria

Phylum Cnidaria Radial symmetry Mouth at oral end surrounded by tentacles. One opening into and out of gastrovascular cavity. Cnidocytes that discharge pneumatocysts Two body forms Polyp Medusa Two germ layers Nerve net

Radial symmetry

Mouth and Tentacles

Cnidarians are the oldest existing animals that have specialized tissues. Cnidarians have two body forms. polyps In the polyp form of a coral, the tentacles and mouth face upward.

medusas In the medusa form of a jellyfish, the tentacles and mouth face downward.

The four major cnidarian classes are defined by their dominant body form. Anthozoans such as sea anemones have a dominant polyp stage.

The four major cnidarian classes are defined by their dominant body form. Hydrozoans such as hydra alternate between forms.

The four major cnidarian classes are defined by their dominant body form. Scyphozoans are jellyfish with a dominant medusa form.

The four major cnidarian classes are defined by their dominant body form. Cubozoans such as sea wasps have a dominant medusa form.

Fig. 13.2 Fig. 13.2

Generalized Cnidarian Life Cycle Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Generalized Cnidarian Life Cycle

Cnidocyte Structure and Nematocyst Discharge Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cnidocyte Structure and Nematocyst Discharge

Cnidarians are made up of two tissue layers separated by mesoglea. gastrovascular cavity mouth mesoglea tentacle oral arms The outer tissue layer has three cell types. contracting cells nerve cells cnidocytes (which contain nematocysts) barbs coiled nematocyst discharged

Nervous System Nerve cells, arranged in a nerve net.

Class Hydrozoa Freshwater & marine. Cnidocytes present only on epidermis. Medusa (if present) with a muscular velum. Mesoglea without ameboid cells. Asexual reproduction by budding. Sexual reproduction via gametes produced by epidermis & released into water.

Class Hydrozoa Hydra Obelia Gonionemus Physalia

Class Hydrozoa Hydra Encapsulated embryo Ovaries Budding Spermaries Sexual cycle Asexual cycle

Hydra Body Wall Gastrovascular cavity Gastrodermis Mesoglea Epidermis

Fig. 13.9

Obelia

Obelia Gonangium Medusae Medusa bud

Class Hydrozoa Gonionemus Fig. 13.12b

Class Hydrozoa Gonionemus Velum

Class Hydrozoa Physalia

Class Scyphozoa Tentacles up to 70 meters in length Cnidocytes present in gastrodermis & epidermis Thick mesoglea contains ameboid cells Gametes produced by gastrodermis All marine

Class Scyphozoa Aurelia

Copyright © The McGraw-Hill Companies, Inc Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Aurelia Life History

Fig. 13.18 Fig. 13.18

Planula Larva Ciliated larva that can swim to a new location

Aurelia Mesoglea Eggs Gastrovascular cavity Mouth

Aurelia Oral arm Gastric pouch Mouth Tentacles

Class Cubozoa Medusa dominant & cuboid Tentacles arise at four corners from blade-like pendalium. All marine Strong swimmers which prey primarily on fish Stings of some may be fatal within minutes to humans.

Class Cubozoa Gonad Pedalium Tentacle

Class Cubozoa Chironex Sea Wasp

Class Anthozoa Medusa stage absent Solitary or colonial Some produce protective skeletons Gastrovascular cavity subdivided by at least 8 mesenteries Cnidocytes on mesenteries Mesoglea contains ameboid cells All Marine

Class Anthozoa Sea Anemone

Class Anthrozoa Metridium Tentacles Mouth Pharynx Septum Gastrovascular cavity

Symbiosis

Sea Anenome Feeding

Class Anthozoa Corals Protective skeleton of calcium carbonate Polyp retracts when not feeding

Zooxanthellae Photosynthetic dinoflagellates (brown) Live in corals Provide nutrients for coral by photosynthesis Mutualism

Corals Colony of interconnected polyps

Class Anothozoa Meandrina Brain Coral

Class Anothozoa Gorgonia Sea Fan

Class Anothozoa Tubipora Pipe Organ Coral

Class Anothozoa Actinodiscus Mushroom Coral

Class Anothozoa Acropora Staghorn Coral

Coral Reefs Formed over thousands of years from successive layers of coral skeleton deposits (calcium carbonate forms underwater mountains of coral animal skeletons) The underwater equivalent of the amazon jungle- very high species diversity and biomass Reefs contain sponges, colonial hydrozoans, anemones, many varieties of coral, fish, many types of worms we’ve not discussed, not to mention bryozoans, ctenophores, protists, bacteria, etc etc..

Copyright © The McGraw-Hill Companies, Inc Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Coral Reef Ecosystem Photo © McGraw-Hill Higher Education, Barry Barker, Photographer

Cladogram of Cnidaria Anthozoa Scyphozoa Cubozoa Medusa cuboidal Loss of medusa Hydrozoa Polyp stage reduced Septa divide gastrovascular cavity Radial symmetry, cnidocytes, planula larva

The End