PHYLUM CNIDERIA (JELLYFISH, CORAL)
• There are over 10,000 species. • No organs. No brain. They do have gastrovascular cavities, where digestion occurs
• ALL have some type of stinging organelle. •Simple nervous system consisting of a nerve net; aquatic floating or sessile.
• Live in marine aquatic environments. • Cniderians are all predators.
TYPES
Hydrozoa - Fresh water cniderians
Scyphozoa - Swimming jellyfish
Anthozoa - Sea Anemones, Corals
Cubozoa - Box Jellies
SYMMETRY
Cniderians have two major body forms––medusa and polyp––both of which are radially symmetrical.
REPRODUCTION
Cniderians reproduce both sexually (external) and asexually. In sexual reproduction, the male jellyfish releases sperm and the female releases eggs into the water, leading to the production of a zygote that develops into a free-floating larvae, which will soon grow into a polyp. Asexual reproduction occurs through budding. See below for more info on reproduction. Not to be confused with the alternation of generations in plants. In plants, one generation is haploid while the other is diploid, but in cnidarians, both polyps and medusae are diploid.
WHAT'S THE DIFFERENCE BETWEEN A MEDUSA AND POLYP?
A polyp is cylindrical and sessile. Reproduces asexually through budding to produce new medusae. Example = sea anemone.
A medusa is is shaped like an umbrella and free swimming. It is found in open waters. Example = Sea jelly.
WHY THE TENTACLES?
ALL cniderians have tentacles with stinging cells known as cnidocytes, which contain nematocysts, or capsules that hold coiled, thread-like tubes containing poison and barbs; these nematocysts function like harpoons. Remember that osmosis is the diffusion of water through a selectively permeable membrane. The pressure provided by this flow of water is called osmotic pressure. The water inside an undischarged nematocyst is under an osmotic pressure of more than 150 atmospheres! This pressure is about 20 times greater than the pressure in an inflated bicycle tire. Theses tentacles capture, sting, and subdue prey. Without this tentacles, these cnidarians wouldn't be able to capture and eat their prey.
MY THOUGHTS
Cniderians are older than the dinosaurs, which is pretty interesting. I'm also intrigued by the form of mutualism that exists between clown fish and sea anemones. The clown fish are protected from predators by the sea anemone, as they have anatomical adaptations that prevent them from getting stung. Finally, I'm also intrigued by the medical applications of some cnidarians. A calcium phosphate mineral in coral known as hydroxyapatite can be treated so that it has the same structure and chemical composition of human bone. Thus, the mineral can be used in face or jaw reconstruction as well as in arm and leg surgery. They anchor to the adjacent bone and are eventually replaced by new human bone growth.
• ALL have some type of stinging organelle. •Simple nervous system consisting of a nerve net; aquatic floating or sessile.
• Live in marine aquatic environments. • Cniderians are all predators.
TYPES
Hydrozoa - Fresh water cniderians
Scyphozoa - Swimming jellyfish
Anthozoa - Sea Anemones, Corals
Cubozoa - Box Jellies
SYMMETRY
Cniderians have two major body forms––medusa and polyp––both of which are radially symmetrical.
REPRODUCTION
Cniderians reproduce both sexually (external) and asexually. In sexual reproduction, the male jellyfish releases sperm and the female releases eggs into the water, leading to the production of a zygote that develops into a free-floating larvae, which will soon grow into a polyp. Asexual reproduction occurs through budding. See below for more info on reproduction. Not to be confused with the alternation of generations in plants. In plants, one generation is haploid while the other is diploid, but in cnidarians, both polyps and medusae are diploid.
WHAT'S THE DIFFERENCE BETWEEN A MEDUSA AND POLYP?
A polyp is cylindrical and sessile. Reproduces asexually through budding to produce new medusae. Example = sea anemone.
A medusa is is shaped like an umbrella and free swimming. It is found in open waters. Example = Sea jelly.
WHY THE TENTACLES?
ALL cniderians have tentacles with stinging cells known as cnidocytes, which contain nematocysts, or capsules that hold coiled, thread-like tubes containing poison and barbs; these nematocysts function like harpoons. Remember that osmosis is the diffusion of water through a selectively permeable membrane. The pressure provided by this flow of water is called osmotic pressure. The water inside an undischarged nematocyst is under an osmotic pressure of more than 150 atmospheres! This pressure is about 20 times greater than the pressure in an inflated bicycle tire. Theses tentacles capture, sting, and subdue prey. Without this tentacles, these cnidarians wouldn't be able to capture and eat their prey.
MY THOUGHTS
Cniderians are older than the dinosaurs, which is pretty interesting. I'm also intrigued by the form of mutualism that exists between clown fish and sea anemones. The clown fish are protected from predators by the sea anemone, as they have anatomical adaptations that prevent them from getting stung. Finally, I'm also intrigued by the medical applications of some cnidarians. A calcium phosphate mineral in coral known as hydroxyapatite can be treated so that it has the same structure and chemical composition of human bone. Thus, the mineral can be used in face or jaw reconstruction as well as in arm and leg surgery. They anchor to the adjacent bone and are eventually replaced by new human bone growth.