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What are the two Phyla included in this group?
Cnidaria and Ctenophora
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.
- 1. Epidermis
- 2. Mesoglea
- 3. Gastrodermis
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.
- 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.
Describe the structure and function of a Cnidocyte.
- 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.
List the four cell types found in the Gastrodermis of a Cnidaria and describe their basic function.
- 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
Describe the structure and function of the mesoglea in Cnidaria.
- 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.
Name and describe the two body forms possible for a Cnidaria.
- 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)
Name the four classes of Cnidaria.
Hydrozoa (The Hydras), Seyphozoa (The Jellyfish), Cubozoa (The Box Jellyfish and Sea Wasps) and Anthrozoa (The Corals and Anemones)
List three characteristics of the class Hydrozoa.
- 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)
List three characteristics of the class Seyphozoa.
- 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.
List three characteristics of the Cubozoa class.
- 1. Box-shaped medusa stage
- 2. Complex eyes around medusa fringe
- 3. Very deadly species eg. Sea Wasp and Portuguese Man O' War.
List two characteristics of the Anthrozoa class.
- 1. Occur only as polyps (medusa stage absent)
- 2. May be solitary (anemones & some corals) or colonial (some corals)
Are the phyla Ctenophora shallow or deep water organisms?
Are the Ctenophora mostly free swimming or sessile?
List two facts about the evolution of Ctenophora.
- 1. Low diversity (about 100 spp)
- 2. Most basal known lineage of animals. (May be older than Porifera)
List three things that Ctenophora have in common with Cnidaria.
- 1. Tissue level of organisation
- 2. Diploblastic
- 3. Biradial symmetry
Do Ctenophora have a combined mouth/anus or two separate openings?
Separate mouth and anus.
How do the Ctenophora swim?
Using comb rows consisting of comb plates that have beating cilia to cause forward or reverse movement.
How do Ctenophora catch prey?
Using colloblasts on their tentacles that secrete sticky adhesive granules that trap prey.
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