Phylum Cnidaria (the "C" is silent) consists of sea anemones, corals, hydra, and jellies. These were the first animals to exhibit tissues in addition to specialized cells, but they do not have any organs. The also have body plans with radial symmetry. Cnidarians were the first free-swimming animals. In fact, they were the first animals to have a lot of what we take for granted today.
Having a mouth that leads to a digestive cavity allows cnidarian to store their food while they digest it. This allows them to eat larger food that sponges can.
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Not only do cnidarians have controlled movement, they are able to direct their movement because they have a nerve net around their mouths that detects food.
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Nematocysts
Cnidarians have specialized stinging cells lining their tentacles called nematocyst which they use to actively hunt their prey that approaches them.
Cnidarians have specialized stinging cells lining their tentacles called nematocyst which they use to actively hunt their prey that approaches them.
These cell fire off needles, like microscopic syringes, that deliver neurotoxins or venom. The neurotoxin paralyzes prey allowing the cnidarian to pull it into their mouth and slowly digest it in their gastrovascular cavity. Undigested food leaves through the mouth since cnidarians only have one opening to their endoderm.
Because nematocyst are triggered as a reflex response to touch or chemical change and not a nerve response, they will still fire if the animal is dead. So never touch a dead cnidarian, they will still sting.
First to Move
Cnidarians were the first animals to move. Not only did they have the first tissues similar to muscles, they were the first to swim freely. Even some anemones can swim! https://vimeo.com/37443347
Cnidarians were the first animals to move. Not only did they have the first tissues similar to muscles, they were the first to swim freely. Even some anemones can swim! https://vimeo.com/37443347
Polymorphism
Cnidarians exist in two forms, and some of these animal exhibit both forms in one lifetime. Polyps are typically sessile and stay attached to a surface while medusas are able to swim freely.
Cnidarians exist in two forms, and some of these animal exhibit both forms in one lifetime. Polyps are typically sessile and stay attached to a surface while medusas are able to swim freely.
Class Anthozoa
Class Anthozoa includes polyp animals like sea anemones and corals. Unlike other cnidarians, anthozoans do not have a medusa stage in their development. Instead, they release sperm and eggs that form a planula, which attaches to some substrate on which the cnidarian grows. Some anthozoans can also reproduce asexually through budding.
Class Anthozoa includes polyp animals like sea anemones and corals. Unlike other cnidarians, anthozoans do not have a medusa stage in their development. Instead, they release sperm and eggs that form a planula, which attaches to some substrate on which the cnidarian grows. Some anthozoans can also reproduce asexually through budding.
Coral
Coral is a small polyp animal that live in colonies. Hard corals produce a limestone cup to live and hide in. The limestone cups of all the coral in the colony make up a hard coral reef. Each coral polyp lives alongside a single-celled algae called zooxanthellae. This algae is what give the coral reef its beautiful colors. When conditions become unfavorable for coral, the algae dies and the coral becomes "bleached" and ceases to grow. Coral requires precise temperatures, water depth, light exposure, and silt levels in order to survive.
Coral is a small polyp animal that live in colonies. Hard corals produce a limestone cup to live and hide in. The limestone cups of all the coral in the colony make up a hard coral reef. Each coral polyp lives alongside a single-celled algae called zooxanthellae. This algae is what give the coral reef its beautiful colors. When conditions become unfavorable for coral, the algae dies and the coral becomes "bleached" and ceases to grow. Coral requires precise temperatures, water depth, light exposure, and silt levels in order to survive.
Fire Coral
is actually a
hydrozoan
and will sting if touched
Soft corals are also composed of some rigid calcium carbonate, but it is blended with protein so it is less rigid than hard corals. These corals are “rooted,” but because they have no exoskeletons, they sway back and forth with the currents, appearing to be more like plants blowing in the breeze. They include Sea Fans, Sea Pens, Flower Corals, and Bubble Corals.
Sea Anemones
Sea Anemones are also polyps and range in size from a diameter of half an inch to six feet! Sea anemones are essentially the large scale version of a coral animal. Sea anemones are carnivorous predators but they share a very special relationship with clownfish called symbiosis.
Class Scyphozoa (true jellies)
Coming from the Greek word for cup, scyphozoans exhibit a medusa form as adults and propel themselves by contracting their bodies, pushing the water out of their cup, propelling them forward. Most species exhibit both medusa and polyp phases at different times in their lives.
Here's a link to the Power Point presentation
Coming from the Greek word for cup, scyphozoans exhibit a medusa form as adults and propel themselves by contracting their bodies, pushing the water out of their cup, propelling them forward. Most species exhibit both medusa and polyp phases at different times in their lives.
Here's a link to the Power Point presentation
NJ Jellies
Other Jellies (class Hyrdazoa and Cubozoa)
Portuguese Man O'Wars are actually a colony of animals in phylum Hydrozoa. The "float" they share can be anywhere from 4 inches to two feet with tentacles reaching up to 60 feet long. In extremely rare cases, their stings can also lead to death. Other hydrozoans, like small polyps called hydra, can live in fresh water.
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ALWAY REMEMBER: NEVER TOUCH A DEAD JELLYFISH AND DO NOT PEE ON THE STING!!!
Review what you learned with this Cnidaria Quizlet
Many of the moving gifs on this page were created from Shape of Life using the gif maker on giphy.com