CNIDARIANS

What makes Cnidarians Unique?

• Cnidarians are group of animals that are very diverse from stony coral to jellyfish. What common thread keeps this phyla of animals together?

Common Thread

• Cniadarians are DIPLOBLASTIC (2 Layers – epidermis and gastrodermis)

• TRUE TISSUES(muscular, nervous, gastric)• CNIDAE (stinging tentacles)

Diploblastic Body

• The two tissue layers are the epidermis and the gastrodermis

• Mesoglea- Jelly like portion between that separates the two layers.

True Tissues

• True tissues: muscular, nervous, gastric

Cnidae

Cnidocytes used in defense, feeding, and attachment

Some Cnidocytes can produce Nematocysts or stinging cells

Nematocysts

Food gathering and defense.

Long tube with spines that penetrates prey delivering toxin

Nematocysts

Two Body Forms

• Polyp: tentacle up (anenomes, coral, hydra)

• Medusa: tentacle down (jellyfish)

Polyp Stage

• Sessile, Asexual Reproduction, usually attached to substrate, some “walk”

Polyp Stage

• Budding• Fission

Polyp Stage

Polymorphism in polyps

Medusa Stage• Dioecious, free swimming, sexual

reproduction• Develop reproductive organs (testis and

ovaries)

Reproduction

• Sexual and Asexual reproduction• Alternation of generations

Reproduction (sexual)

• Egg and Sperm released from GVC• Once combined egg + sperm will form a

planula (free swimming larva)• Once GVC devolops forms a Polyp

Reproduction (asexual)

• Budding• Fission

Alteration of Generations

• 2 Stages: Polyp & Medusa (dimorphic)• Polyp Stage – some species asexual

reproduction by budding, usually sessile

Nutrition• Gastrovascular Cavity: Functions in

digestion, the exchange of respiratory gases, metabolic waste, and release of gametes

Nutrition• Feeding: Prey mostly small crustaceans

(copepods) • Nematocysts paralyze prey, contractile

cells move prey to mouth, GVC releases enzymes

Skeletal System

• Hydrostatic – fluid filled body (mesoglea)• Epitheliomuscular cells (longitudinal and

circular)

Nervous System

• Nerve Net – Nervous system is spread throughout entire body

• Most primitive nervous system

• Some sensory structures – ocelli sense light

Circulation, excretion, respiration

• No special structures or tissues, these life functions are carried out directly with the environment

Hydrozoa

• Alteration of generation• Mostly Marine (although a few freshwater)

Hydra

Obelia

Physalia

Scyphozoa

• True Jellyfish• Mostly found in Medusa stage• Some harmful some not to humans• Ocelli (rhodopalia) allow for Phototaxis

(move toward light)

Cubozoa

• Box Jelly Fish• Some possess

dangerous nematocysts

• Active swimmers and feeders

• Tentacles on corners of medussa

Anthozoa

• Corals & Anemones• Lack medusa stage

Anemones

• Can move slowly over some surfaces• Live as individuals but in colonies• Feed on fish and crustaceans or organic

debris

Corals

• Secrete a calcium skeleton

• Stony coral, large polyped stony corals, and soft corals

• May use symbiotic algae called zooxanthelle for autotrophism.

• Can live individually or in groups.

Zooxanthelle

• Symbiotic Algae that provides food for the coral

• Found in reef-building coral

Soft Coral• No hard calcium skeleton (although may

contain fragments inside them)

Large Polyped Stony Coral (Octocoral)

• Have both soft tissue as well as produces a hard calcium skeleton

Stony Corals

• Little soft tissue mainly hard calcium skeleton

Reef building

• Corals can grow on one another to create entire reef systems

Issues Affecting Reefs

• Many Reef Ecosystems are in peril from being destroyed.

• There are many culprits aiding in destruction of the reefs.