1. Phylum Cnidaria

2. General Information: Cnidaria means ‘a stinging thread’
Examples: sea anemones, corals, jellyfish, freshwater Hydra, and the Portuguese man-of-war
Habitat: marine and fresh water

3. Sea Anemone, Clover Point, Victoria B.C.
                                                                                   
Soft Coral
Sea Anemone, Clover Point, Victoria B.C.

4. Portuguese Man Of War
Brain Coral

6. Corals are an important part of BC marine ecosystems!
In BC, deep water corals such as the red tree or “Gorgonian coral” provide shelter for juvenile rockfish such as the yelloweye rockfish or sharpchin rockfish

7. Characteristics:
All cnidarians have a basic radial symmetry and possess only 2 layers of living tissues.
2 tissue layers: ectoderm and endoderm
Contain a mesoglea
Some possess an exoskeleton (for protection) made up of CaCO3 (e.g. corals)

9. Characteristics Have 2 body forms:
a. Polyp (sessile) – e.g. hydra, coral, or sea anemone
b. Medusa (free swimming) – bell shaped – e.g. jellyfish

10. Some cnidarians contain only one body shape during their life cycle, while others contain both during their life cycle
When a cnidarian exhibits the 2 body forms in its life cycle, it is called polymorphism (‘many shapes’)
The evolution of a primitive nervous system sets these organisms apart from the sponges – called a nerve net
They contain nematocysts found on the tentacles used for capturing prey and for protection

14. Mesoglea is sandwiched between ectoderm and endoderm
There are amoebocytes in the mesoglea of cnidarians, much like in sponges
Cnidarians possess a simple digestive system – the gastrovascular cavity – where digestion and circulation of nutrients occur

16. Sea Anemones – Class Anthozoa:
No medusa stage
They are all marine
Polyp body form exclusively
Reproduce asexually through longitudinal or transverse fission (like binary fission, but on a much larger scale)
Are primarily carnivorous – capture food using nematocyst-studded tentacles and transfer it to a central mouth opening
There are around 6000 species of sea anemones

17. Coral – Class Anthozoa Colonial form of Class Anthozoa
Can have soft and hard corals
Hard corals secrete external CaCO3­ skeletons and are called ‘stony corals’
Stony corals make up coral reefs (not all make reefs though)
Coral add about 10 kg of additional CaCO3 per m2 of reef yearly
Soft corals do not have hard external skeletons

18. The Anatomy of A Coral
Many corals have symbiotic green algae called zooxanthellae living in their polyps
Warmer ocean temperatures can cause these algae to die, resulting in a phenomenon known as “coral bleaching”

20. Jelly Fish – Class Scyphozoa
Only a few hundred species – nearly all are marine
The body is in the form of an inverted cup, with nematocyst-studded tentacles extending downward from the cup.
Some jellyfish have symbiotic unicellular algae that give them nutrients
The life cycle of jelly fish involves the two different body forms: polyp and medusa

21. A Typical Jellyfish Life Cycle

23. A Typical Cnidarian - Hydra
Structure:
Polyp body form
Locomotion:
Sessile; however, some
can somersault and glide
along while secreting mucus

24. Ingestion, Digestion, Elimination
Food is captured by nematocysts in the tentacles by stinging or stunning prey
Tentacles push food through mouth into gastrovascular cavity
Flagella line the endoderm layer and create a current
The endoderm cells secrete enzymes to break down food
Food is taken into cells and nutrients are circulated by amoeboid cells
Wastes are eliminated out through the mouth

25. The Nematocyst
Nematocysts vary in shape, but all are adapted for stinging or stunning prey
In the sea anemone on the right, nematocyst aggregations are visible as the dark pink lines

26. Respiration O2 enters the cells by diffusion
CO2 leaves the cells by diffusion

27. Nervous System Have a nerve net within the mesoglea
When stimulated, the nerve net will respond by contracting / relaxing the muscles
Have sensory cells that are sensitive to touch, light, chemicals, and balance

29. Muscular System
Latitudinal and circular muscle fibres are found in the endo / ectoderm layers

30. Excretion Nitrogenous wastes leave the cells by diffusion
Wastes enter the gastrovasuclar cavity and leave via the mouth

31. Reproductive System A. Asexual Budding (bud breaks away)
Regeneration (re-growth of missing parts)
A Hydra Budding

32. Reproductive System B. Sexual Some are hermaphrodites
Ovaries and testes grow on the side of adults
Ovary produces an egg and remains attached to the adult
Testes produce the sperm which swim to the egg, resulting in a zygote
Zygote develops into a ball of cells called the blastula, which develops into a ciliated larva called a planula, which can swim to another location, settle, and develop into a polyp adult

34. Ecological Importance of Cnidarians
Are extremely important in the ecology of tropical and temperate oceans in the form of coral (eg Great Barrier Reef)
Corals provide habitats and food for many species of fish and invertebrates
Reefs protect the land from ocean waves
Cnidarians form symbiotic relationships with other organisms living among the tentacles (clown fish and sea anemones)

35. The Importance of Deepwater Corals
Throughout the world, many deepwater coral reefs are being destroyed by trawlers, removing vital nursery grounds for many fish species

36. Cnidarians and Medicine
Used in medical research for their chemicals (cancer therapy)
Stony corals are now being used in certain surgical procedures. Because they have many pores for blood vessels to grow through, small pieces of coral are now being used in bone grafts, particularly in face and jaw reconstruction, and in arm and leg surgery
These pieces are eventually replaced by normal bone tissue

37. Evolutionary Significance
Cnidarians are the first animals to have organized true cell tissues
They are therefore the first true multicellular organisms to appear
They are the first organisms to have muscle tissue and nervous tissue
Cnidarians, having radial symmetry are thought to share a common ancestor with all other multicellular animals