Cnidaria
Eukaryotes - Kingdom Animalia
Phylum Cnidaria
- Sea anemones, jellyfish, and corals
- Cells organized into tissues
- Motile, and responsive to environmental conditions
- Display radial symmetry in two different forms (polyp or medusa)
- Centrally located mouth surrounded by tentacles with nematocysts to sting prey
Radial Symmetry
Cnidarian Forms
- Polyp; pictured left
- Medusa; pictured right
Cnidarian Structures
- Mouth surrounded by tentacles
- Contain nematocyst for stinging
- Mouth leads to gut
- Where food is digested
Cnidarian Anatomy
- Almost all carnivorous
- Use nematocysts to sting/poison prey
- Digestion starts extracellular and intracellular digestion continues in gut
- Lack a brain and true nerves, but do have nerve cells
- Nerve net transmits impulses in all directions
- Can be used to identify members of the same species and attack those who are not
- Some have primitive “eyes”
- Statocysts are sensitive hairs that provide a sense of balance
Class Hydrozoa
- Alternate between medusa and polyp stages
- Medusa stage hard to distinguish between Class Scyphozoa
- Some live in free-floating colonies, others in attached colonies and resemble corals
Typical Hydrozoa Life Cycle
- Reproductive polyps produce planktonic medusa
- Medusa release gametes into ocean
- Fertilized egg become planula (larvae)
- Planula form hydroid colony as polyp form
Class Scyphozoa
- Larger jellyfish
- Medusa is dominant stage in life cycle
- Swim by contracting bell
- Currents impact movement
- Some members have fatal stings
Typical Scyphozoa Life Cycle
- Adult medusa release egg or sperm
- Egg and sperm develop into planula
- Planula find place to attach and develop into scyphistoma → strobila → ephyra
- Ephyra develop into medusa and mature
Class Anthozoa
- Largest class
- Lack medusa stage
- Solitary or colonial
- Sea anemones
- Corals
- Gut lined with septa
- Increase surface area for digestion
- Provide support
- Forms
- Sea Anemone – obvious polyp
- Corals – polyp form, but large variety in shape and size
Examples
Class Anthozoa Structure
Class Anthozoa: Corals
- Gorgonians - pictured at the right!
- Colonial
- Branching skeleton made of protein
- Exist in cold water, form reefs in tropical water
- Ex: sea fan
- Precious
- Gorgonians with red or pink calcareous spicules + protein skeleton
- Black
- Hard black protein skeleton
- Soft
- Fleshy colonies with large polyps and no hard skeletons
Phylum Ctenophora
- Comb jellies
- Swim using ciliary combs (scatter light as they move to produce rainbow effect)
- Capture prey using sticky cells on tentacles (colloblasts)
- Most live near the surface and are transparent, but some that live in deeper waters are pigmented