Cnidarians

By: Camila Ciochon

Professor Larry Frolich

Miami-Dade College

Z003021

Phylum Cnidaria

Also called Coelenterate.

Diversity of Cnidarians

Classes:

1. Hydrozoa

2. Scyphozoa

3. Cubozoa

4. Anthozoa

5. Staurozoa (medusa-like)

6. Myxozoa (parasitic form)

Overview

Classifications:

Kingdom: Animalia

Phylum: Cnidaria

Four Major Classes:

Anthozoa (sea anemones, corals)
Cubozoa (box jellyfish)
Hydrozoa (hydrozoans, also known as hydromedusae or hydroids)
Scyphozoa or Scyphomedusae (jellyfish)

Structure& Characteristics:

Multicellular
Live in fresh and saltwater
Have stinging cells called nematocytes
Radial Symmetry
No Nervous system (they have a nerve net)

Ecological Relationships

Cnidarian morphology:

Cnidarians have two distinct body plans, the medusa (a) and the polyp (b).

There are two distinct cnidarian body forms: polypoid and medusoid.

Both polyp and medusa forms consist of a digestive sac, the coelenteron, surrounded by two layers of tissue, the endoderm and the ectoderm.

All cnidarians have two membrane layers, with a jelly-like mesoglea between them .

A gelatinous matrix called the mesoglea lies between the two layers and may contain loose aggregations of cells.

Outer layer of cells is for protection. (exoderm)

Inner layer is mostly for digestion. (endoderm)

Cnidocytes: stinging cells

contain large organelles called (a) nematocysts that store a coiled thread and barb.

When hairlike projections on the cell surface are touched, (b) the thread, barb, and a toxin are fired from the organelle.

Evolutionary Tree:

ANATOMY/Morphology & Physiology

Most Anthozoan (coral & anemone) species exist exclusively in the polyp form and are therefore primarily sessile.
Hydrozoa (hydroids) are classified based on the presence of a membrane called the velum that lines the inside edge of the bell in the medusa forms.
Cubozoa(box jellyfish) are cube-shaped while Scyphozoa (jellyfish) are bell-shaped, and they have different venom as well.

How this group works.

1. How does it get oxygen? How does the blood circulate?

Both cell layers have cells that contract like muscles

Cell layers are derived from the ectoderm and endoderm of the embryo.

Anthozoa- “flower animals” Oxygen diffuses directly into body cells from the water and carbon dioxide and other wastes diffuse out of the cells directly into the surrounding water.

2. How does it obtain and digest its food?

Cnidarians are carnivorous with hydras and corals consuming plankton and some sea anemones consuming small fish

Medusa & Polyp Cells adapted for digestion release enzymes over newly captured prey.

The inner cell layer surrounds the gastrovascular cavity- where digestion takes place.

3. How does it eliminate waste and regulate its internal chemistry?

Undigested food is ejected out of the mouth.

4 How does it move through the environment?

Hydra live independently in freshwater streams and ponds.

They attach themselves to materials via a basal disc.

Move by floating, gliding. and somersaulting.

Primitive animals.

5. Where do they live? Do they have any Predators?

Hydra live independently in freshwater streams and ponds.

Cnidaria is a phylum containing over 9,000 species found only in aquatic and mostly marine environments.

Predators: Sharks, tuna, sea turtles.

6. How do they reproduce? Cnidarian Gas Exchange

Cnidarians do not have a nervous system.

Cnidarians have a nerve net.

Nerve net- conducts nerve impulses from all parts of the body, but there is no control center like a brain.

Impulses from the nerve net bring about contractions of muscle like cells in the tentacles and bodies of cnidarians

Nervous Regulation have the ability to reproduce sexually and asexually.

Asexual reproduction by budding small buds grow as extensions of the body

The medusa form is the sexual stage which alternates from generation to generation with the asexual polyp life cycle

The Portuguese man-of-war lives as a colonial polyp.

A single polyp multiplies by budding, forming a colony .

Medusa reproduce sexually to produce polyps which in turn, reproduce asexually to form new medusa

7. What is their life cycle?

Have both a polyp and medusa in life cycle,

Some are feeding or reproductive

Digestion in Cnidarians

Examples: Hydra, The Portuguese Man O' War

"Bell-shaped" (or medusoid) to start. The body of a jellyfish allows it to propel itself using muscle contractions - or float along water currents.

LIFE CYCLES

Incredible Anthozoa building forms and how they create an entire ecosystem!

Sea anemones and corals

Marine polyps that inhabit coastal areas.
Has a basal disc like hydra which attaches to rocks
Sea anemone is solitary and feeds on fish and crabs that swim nearby
Corals resemble anemones but have skeletons and live in colonies Anthozoa- “flower animals” Soft coral have internal skeletons, precious coral
Stony coral has an external skeleton made of limestone
Skeletons of dead corals accumulate and form reefs