Radiata

Cnidaria and Ctenophora

Radial or Biradial symmetry and diploblastic development.

Radial - body shape where ANY slice through the centre of the organism would divide the animal into equal halves. Biradial - at least one set of structures is paired, resulting in only two planes of symmetry.

This is when an organism develops from two embryonic tissue layers, separated by a non-cellular layer. (Ectoderm, mesoglea and endoderm) This is achieved through gastrulation of the blastula into a gastrula.

They diverged from sponges c. 700 mya. They are diverse; with over 10000 living species.

• 1. Mostly marine: most prefer shallow tropical seas, a few live in fresh water.
• 2. All are carnivorous.
• 3. May be solitary or colonial.
• 4.Can be sessile, floating, or slow moving. Can alternate in different stages of the life cycle.

Main part of the body is a body stalk which is hollow, containing a gastrovascular cavity. This has a single opening which serves as both a mouth and an anus. The mouth/anus is surrounded by a hypostome attached to which is a whorl of tentacles.

• 1. Epidermis
• 2. Mesoglea
• 3. Gastrodermis

It is the outer layer contacting the environment, consisting of tightly packed cells resting on a basal membrane. It tightly regulates what passes through the body wall.

• 1. Epitheliomuscular cells - serve as a protective layer and muscle contraction (cell base contains contractile myofibrils)
• 2. Nerve cells. - Form a nerve net which conducts in all directions.
• 3. Sensory cells - balance, touch, light, chemosensory ("taste/smell")
• 4. Gland cells - Secrete glue for attachment and sometimes release gas bubbles for floating.
• 5. Cnidocytes - Stinging cells
• 6. Interstitial cells - undifferentiated cells which form any of the above (except 1 that reproduce themselves), and gametes.

• 
• Stinging cells used for feeding and defence located on the tentacles of a Cnidaria.
• Each has a stinging capsule (nematocyst) containing a coiled stinging thread that
• everts when the "trigger" is touched and injects venom into the prey/preadetor.

• 1. Nutritive cells - Muscular cells that may have cilia (create water flow)
• 2. Gland cells - Secrete enzymes for digestion and mucous for lubrication
• 3. Nerve cells - Sensory input and motor output (sometimes found)
• 4. Interstitial cells - Can form the above cell types

• A non-cellular, gelatinous layer between the epidermis and gastrodermis that provides skeletal support and buoyancy in medusa forms.
• In some Cnidaria, epidermal and endodermal cells migrate into the mesoglea.

• Polyp - Generally the sessile form. Upright, with tentacles and mouth/anus on the superficial surface.
• Medusa - Inverted polyp, mobile form: swims by contracting the "bell". Has a think mesoglea for buoyancy)

Hydrozoa (The Hydras), Seyphozoa (The Jellyfish), Cubozoa (The Box Jellyfish and Sea Wasps) and Anthrozoa (The Corals and Anemones)

• 1. Mostly marine.
• 2. Mostly colonial
• 3. Life cycle usually alternates between a polyp (The most conspicuous stage, usually reproduces asexually by budding) and a medusa form (reproduces sexually)

• 1. All marine with medusa form as the main stage in the life cycle.
• 2. Most coastal species have brief sessile polyp stage.
• 3. Open ocean species generally lack the polyp stage, instead they form part of the plankton.

• 1. Box-shaped medusa stage
• 2. Complex eyes around medusa fringe
• 3. Very deadly species eg. Sea Wasp and Portuguese Man O' War.

• 1. Occur only as polyps (medusa stage absent)
• 2. May be solitary (anemones & some corals) or colonial (some corals)

Deep water

Free swimming.

• 1. Low diversity (about 100 spp)
• 2. Most basal known lineage of animals. (May be older than Porifera)

• 1. Tissue level of organisation
• 2. Diploblastic
• 3. Biradial symmetry

Separate mouth and anus.

Using comb rows consisting of comb plates that have beating cilia to cause forward or reverse movement.

Using colloblasts on their tentacles that secrete sticky adhesive granules that trap prey.