The
Phylum Cnidaria is made up hydroids, jellyfish, anemones, hydras and corals.
The two latter groups of animals will not be discussed in this book as
they are not found intertidally. Cnidarians have a radially symmetrical
body that consists of three layers. The outer layer is called the epidermis.
The mesoglea is the middle layer which is made up of a jelly-like matrix
and the inner layer is called the gastrodermis which lines the digestive
cavity. The digestive system consists of a mouth that is surrounded by
tentacles and a tube or sac which is where digestion takes place. The
life cycle of certain cnidarians is made up of two stages: the polyp stage
and the medusae stage. Most jellyfish seen in our area are in the sexual
stage of their life cycle where prior to that they were in the polyp stage.
Sea anemones can reproduce either sexually or asexually by budding. A
characteristic which is unique to cnidarians is that they are equipped
with stinging cells called nematocysts which are used to capture prey
and for a means of defense. A nematocyst is a capsule that contains a
long coiled tube, usually armed with barbs or spines, and a toxic mixture.
When the animal comes in contact with prey or a predator, the tube comes
uncoiled and penetrates or wraps around the victimÕs flesh, then injects
the toxin. Humans coming into contact with some cnidarians may have reactions
ranging from a mild rash to severe blistering.
The
Phylum Cnidaria is made up hydroids, jellyfish, anemones, hydras and corals.
The two latter groups of animals will not be discussed in this book as
they are not found intertidally. Cnidarians have a radially symmetrical
body that consists of three layers. The outer layer is called the epidermis.
The mesoglea is the middle layer which is made up of a jelly-like matrix
and the inner layer is called the gastrodermis which lines the digestive
cavity. The digestive system consists of a mouth that is surrounded by
tentacles and a tube or sac which is where digestion takes place. The
life cycle of certain cnidarians is made up of two stages: the polyp stage
and the medusae stage. Most jellyfish seen in our area are in the sexual
stage of their life cycle where prior to that they were in the polyp stage.
Sea anemones can reproduce either sexually or asexually by budding. A
characteristic which is unique to cnidarians is that they are equipped
with stinging cells called nematocysts which are used to capture prey
and for a means of defense. A nematocyst is a capsule that contains a
long coiled tube, usually armed with barbs or spines, and a toxic mixture.
When the animal comes in contact with prey or a predator, the tube comes
uncoiled and penetrates or wraps around the victimÕs flesh, then injects
the toxin. Humans coming into contact with some cnidarians may have reactions
ranging from a mild rash to severe blistering.