Phylum Cnidariastinging-celled animals

• Jellyfishes, corals, anemones• Radial symmetry• Two tissue layers with inner mesoglea • Primitive nerve net but no brain• 2-way digestive tract• Stinging cells for capturing food.

Introduction to Cnidaria

• There are four major groups of cnidarians:1 Anthozoa2 Cubozoa3 Hydrozoa4 Scyphozoa

Body Plans of Cnidarians• Cnidarians have two basic body

forms–medusa –polyp

Medusa• adult jellyfish • free-swimming or floating• usually have umbrella-shaped bodies four-part

symmetry. – The mouth is usually on the concave side, and the

tentacles originate on the rim of the umbrella.

Medusae

Polyps• usually sessile. • have tubular bodies; one end is attached to the

substrate. – The mouth (usually surrounded by tentacles) is found

at the other end. – Polyps may occur alone or in groups of individuals;

different individuals sometimes specialize for different functions, such as reproduction, feeding or defense.

Polyp

Cnidarians are the simplest organisms that have attained a tissue level of organization.

Body Plan

Reproduction

• Reproduction in polyps is by asexual budding (polyps) or sexual formation of gametes (medusa).

– The result of sexual reproduction is a planula larva, which is ciliated and free-swimming.

Characteristics of Cnidaria• Radially Symmetrical • Body multicellular, few tissues, some organelles. • Body contains an internal cavity and a mouth. • Two different forms exist, medusa and polyp

• Reproduction is asexual or sexual.

Characteristics continued• Has a simple net like nervous system

• Has a distinct larval stage which is planktonic • Lives in aquatic environments, mostly marine

• Mostly carnivorous otherwise filter feeders • May have a minimal skeleton of chiton or

calcium carbonate

Polyp life cycle

Medusa life cycle

Class Anthozoa

• The true corals – anemones, and sea pens– Anthozoans do not have a medusa stage

Anthozoa

Sea Pen

Anthozoa

Sea anemone

Anemone

Sea anemone and clown fish

Sea anemone

Aggregating anemones

Brain coral

http://www.imagequest3d.com/cgi-bin/ImageFolio4/imageFolio.cgi?img=&search=coral&cat=aquatic&bool=and

Zooxanthellae and coral

• All cnidarian species can feed by catching prey with nematocysts

• Some of the species have a symbiotic relationship with a dinoflagellate called zooxanthellae.

• The zooxanthellae benefit by using nitrogenous waste and carbon dioxide produced by the host, and the cnidarian (coral) benefits from the photosynthesis and increased calcium carbonate production.

Class Cubozoa• Box jellyfish belong to the class Cubozoa, named for

their cube-shaped medusa• The name sea wasp is applied to some species of

cubozoans• Box jellies can be found in many tropical areas• Box Jellyfish are best known for the extremely

powerful venom possessed by some of their species – Stings from these species are painful, and are

often fatal– The Chironex fleckeri and the Carukia barnesi

species are among the most venomous creatures in the world.

Chironex fleckeri

Class Hydrozoa

• the most diverse group with siphonophores, hydroids, and fire corals

• Hydrozoa are predatory animals which can be solitary or colonial and which mostly live in saltwater. A few genera within this class live in freshwater.

• Some examples of hydrozoans are: Hydra, Obelia, and Portuguese Man o' War (Physalia).

Hydra

Hydras are very small and must be seen with a microscope

Class Scyphozoa

• the true jellyfish• include most of the familiar jellyfish • Their stings may cause skin rashes, muscle cramps,

or even death. • They can be found in every ocean in the world and in

some fresh waters.

Moon Jelly

Fried egg jelly

Ctenophores

• Comb jellies• Bioluminescent• Do not have stinging cells

CtenophoreNot a true jellyfish