Cnidarians

(Coelenterates)

Phylum Cnidaria (Coelenterata)• Class Hydrozoa = Hydra

• POLYP body form = “vase shaped” ; sessile

• Most live in colonies.

1 of 3 classes within Phylum Cnidaria

Phylum Cnidaria (Coelenterata)

• Class Scyphozoa: “Cup Animals”– Medusa body form (bell-shaped); swimming– Commonly known as jellyfish– “Portuguese Man-o-war”– 200 different species

Phylum Cnidaria (Coelenterata)

• Class Anthozoa: “Flower Animals”– 6,100 different species– Sea Anemones, Corals– Coral Reef = 30 degrees North or South of the

equator, shallow water for photosynthetic algae that live in symbiosis with coral

Classification

• Common Name: Hydra

• Scientific Name: Hydra

• Phylum: Cnidaria

• Class: Hydrozoa

• Other: Phylum Coelenterata (Old name)

Major Characteristics

• Body Plan: Hollow, 2 layered sac

• Body Cavity: Endoderm, Mesoglea (jelly like), Ectoderm

• Symmetry: Radial - pull in food from all around

• Cell Specialization: No Organs, Nematocysts = harpoon like stinging cells; neurotoxins cause paralysis

Life Support Processes

• Absorption: Gastroderm; directly into the body wall

• Feeding: tentacles pull food into the mouth; they are carnivores

• Digestion: Gastroderm (endoderm), food vacuoles in cells

• Respiration & Circulation: Gastrovascular inner cavity

Life Support Processes

• Excretion: Mouth opening, diffusion

• Secretion: sticky base for attachment

• Response: Nerve Net - contractile fibers in the epidermis; Ocelli - detects light

• Movement: contractile fibers; tumble motion through the water

• Reproduction: Asexual = budding; sexual = hermaphrodite (no self fertilization)

Life Support Processes

• Support: tissue layers, hydroskeleton

Ecological Relationships• Freshwater living

• Solitary - not colonial like most hydrozoans

• Carnivorous - predatory lifestyle

Body Systems Compared With Humans

• Tissues - layers like our skin

Advancements Over the Previous Phylum

• Nervous Structure

• Movement

• Active Feeding

Diagram of Hydra

• The largest jellyfish is the Arctic Giant Jellyfish: it can have a diameter over 8 ft. with tentacles stretching as long as 120 ft.

• The most venomous jellyfish is the Australian Sea Wasp; death can occur within 1-3 minutes.

• The Great Barrier Reef is the worlds largest stony coral structure stretching for 1,260 miles off Northeast Australia.

Lion’s Mane Jellyfish

Coral Reefs can be visible from the air!

Preventing beach erosion

Great Barrier Reef - Australia