Cnidarians/Ctenophora
Classes (Cnidarians)
Class Hydrozoa--the hydroids
Class Anthozoa--anemones and corals
Class Scyphozoa--the "true" jellies
Class Cubozoa--the box jellies
**Phylum Ctenophora broke off from the Cnidarians recently. Their morphology is essentially the same as Phylum Cnidaria with slight differences discussed later on.**
Class Hydrozoa--the hydroids
Class Anthozoa--anemones and corals
Class Scyphozoa--the "true" jellies
Class Cubozoa--the box jellies
**Phylum Ctenophora broke off from the Cnidarians recently. Their morphology is essentially the same as Phylum Cnidaria with slight differences discussed later on.**
Anatomy
Cnidarians/Ctenophora are considered some of the simplest "higher level" organisms. They are considered acoelomates as they have no lined body cavity. They are diploblastic and radially symmetrical. This means that they are symmetrical from a center point (think of a bicycle wheel). There are 2 basic body shapes: polyps, which remain in one place (anemones/corals); and medusa (jellies), which are weak swimmers that drift along with the currents.
Cnidarians/Ctenophora are considered some of the simplest "higher level" organisms. They are considered acoelomates as they have no lined body cavity. They are diploblastic and radially symmetrical. This means that they are symmetrical from a center point (think of a bicycle wheel). There are 2 basic body shapes: polyps, which remain in one place (anemones/corals); and medusa (jellies), which are weak swimmers that drift along with the currents.
Digestive System
Cnidarians use their tentacles to pull their prey into it's mouth. After digestion, it releases the waste back through the mouth. |
Cnidarians have a hollow central cavity with one opening. This acts as both the mouth and the anus (although it is referred to as the "mouth"). The tentacles are armed with stinging cells called "cnidocytes" that contain structures called "nematocysts" which act as mini harpoons. When the trigger is activitated, the thread-like stinger uncoils and punctures into the prey. Often, these stingers contain toxins which helps to disable the prey.
|
Nervous System
Cnidarians have no brain. A nerve net acts as a simple nervous system that is spread throughout the body but concentrated near the mouth.
Reproductive System
Cnidarians can reproduce both sexually and asexually. Asexual reproduction is achieved through budding, Sexual reproduction occurs by females releasing eggs and males releasing sperm into the water.
Circulatory System
None: The cells will use diffusion to obtain oxygen and nutrients. All of their cells are in contact with the water which allows for nutrient/oxygen transfer.
Examples
Cnidarians have no brain. A nerve net acts as a simple nervous system that is spread throughout the body but concentrated near the mouth.
Reproductive System
Cnidarians can reproduce both sexually and asexually. Asexual reproduction is achieved through budding, Sexual reproduction occurs by females releasing eggs and males releasing sperm into the water.
Circulatory System
None: The cells will use diffusion to obtain oxygen and nutrients. All of their cells are in contact with the water which allows for nutrient/oxygen transfer.
Examples
Hydras:
|
Corals:
|
Sea Anemones:
|
Jellyfish:
|
Ctenophores
Ctenophores are slightly different than Cnidarians. The main differences are:
Ctenophores are slightly different than Cnidarians. The main differences are:
- Ctenophores can be radially or bilaterally symmetrical, Cnidarians are only radially.
- Cnidarians use cnidocytes to stun/capture prey while Ctenophores use colloblasts (a sticky cell). They do not "sting"
- Ctenophores have a complete digestive system--they have an anus separate from the mouth.
- Ctenophores have a comb plate, Cnidarians do not.