Day 7 Cnidaria

Phylum Cnidaria 10,000+ Species


Cnidarian examples include

-Sea Anemones

-Sea Jellies

-Coral

Cnidarian Characteristics

-Radial symmetry or Biradial

-Diploblastic Tissue level (have only 2 layers)

-They have a gelatinous Mesoglea

-Gastrovascular Cavity (this cavity works as their stomach)

-Nerve Net (no brain. The nerve net just responds to stimuli like a reflex)

-Cnidocytes (These are the stinging cells)

What makes Cnidarians stand out is their cnidocytes

-Cnidocytes are stinging cells located on tentacles

-Cnidocytes discharge a harpoon like stinging structure called a nematocyst

Cnidarians have two body structures

-Polyp

-The polyp form is sessile. It attaches to a rock or other surface and tentacles grow upwards. The sea anemone is a polyp form.

-Medusa

-The medusa is a free swimming form. It has a bell on top with tentacles hanging downward. A sea jelly is a medusa form.

Cnidarian Classes

Hydrozoa

-Hydras

Characteristics:

-Cnidocytes present in the epidermis; gametes produced epidermally and always released to the outside of the body; mesoglea is largely ascellular; medusae usually with a velum; many polyps colonial; mostyl marine with some freshwater species

Scyphozoa

-Common Sea Jellies

Characteristics:

-Medusa prominent in the life history; polyp small; gametes gastrodermal in origin; and released into the gastrovascular cavity; cnidocytes present in the gastrodermis as well as epidermis; medusa lacks a velum; medoglea with wandering mesenchyme cells; all are marine

Staurozoa

-polyps

Characteristics:

-Medusae absent; develop from benthic planula larvae; eight tentacles surrounding the mouth; attachment to substrate by adhesive disk; sexual reproduction only; all marine

Cubozoa

-Cube shaped sea jellies

Characteristics:

-Medusa prominent in life history; polyp small; gametes gastrodermal in origin; medusa cuboidal in shape with with tentacles that hang from edges of the bell; all marine

Anthozoa

-Anemones and corals

Characteristics:

-Colonial or solitary polyps; medusae absent; cnidocytes present in the gastrodermis; cnidocils absent gamets gastrodermal in origin; gastrovascular cavity divided by mesenteries that bear nematocysts; internal biradial or bilateral symmetry present; mesoglea with wandering mesenchyme cells; tentacles solid; All marine

Sea jellies have a strange life cycle. They go through a complex alternation of generations

Watch this video on the phyla cnidaria. Create a box in your sketchbook, title it "The Phylum Cnidaria" and take notes, write down interesting things that you learn from the video and include an image in your sketchbook. Make sure you understand the characteristics of cnidaria and their complicated life cycle.