What are the two distinguishing features of this group?
Radial or Biradial symmetry and diploblastic development.
Explain radial and biradial symmetry.
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.
Explain diploblastic development.
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.
List two evolutionary facts about Cnidaria.
They diverged from sponges c. 700 mya. They are diverse; with over 10000 living species.
List four facts about the ecology of Cnidaria.
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.
Describe the basic body shape of a Cnidaria.
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.
Name the three body layers of a Cnidaria.
Describe the function of the epidermis in Cnidaria.
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.
Name and describe the function of the six cell types found in the epidermis of a Cnidaria.
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.