The Basics of Cnidarians
- Biradial: split into 4 parts
- Blind gut: Gut with one opening
- Diploblast: epidermis, gastrodermis, acellular mesoglea
- Planula --> Polyp --> Medusa repeat
- Protosome: mouth first then anus, one opening
Image edited by: John Santiago
The Cells, Structure, and Skeleton Associated with the Cnidaria
Cells and Its Associated Structure Within the Cnidarians
- Cnidocytes: Specialized cells in Cnidaria that specialize in feeding, defense, and attachment. Each cnidocyte are different from each other based on cnida that are located in within them allowing for a differing in function.
- Cnida: Fluid-filled, intracellular capsules that contain a hollow tube
- Nematocysts: Cnidocytes that have a cnida that contain hollow tube containing poison used for predation and protection.
- Epidermis: Lines the outside of the cnidarian and is derived from the ectoderm
- Gastrodermis: Is the inner portion of the cnidarian that functions in digestion and is derived from the endoderm
- Gastrodermis Cavity: This is the blind gut of the Cnidarian that specializes in digestion, water circulation, exchange of gases, and release of metabolic wastes
- Alteration of Generation: Cnidarians involve both polyp and medusa stages
Reproduction
Image from: https://seagrant.uaf.edu/nosb/papers/2011/seward-smack.php
Most Cnidarians possess two body forms:MEDUSA and POLYP.
Polyp is usually asexual and sessile attaching to a substrate at the aboral end, mouth facing up.
Medusa is dioecious and free swimming with mouth facing down. The medusa has more mesoglea than the polyp.
Typically the medusa releases an egg that is fertilized by a free swimming sperm which fertilizes into a zygote into a blastula into a PLANULA which is an elongated freeswimming larva which attaches to a substrate then its interor cells split to form the gastrovascular cavity eventually developing into a polyp which eventually buds producing additional polyps and medusa buds. The Medusae break free of the polyp and swim away.
Polyp is usually asexual and sessile attaching to a substrate at the aboral end, mouth facing up.
Medusa is dioecious and free swimming with mouth facing down. The medusa has more mesoglea than the polyp.
Typically the medusa releases an egg that is fertilized by a free swimming sperm which fertilizes into a zygote into a blastula into a PLANULA which is an elongated freeswimming larva which attaches to a substrate then its interor cells split to form the gastrovascular cavity eventually developing into a polyp which eventually buds producing additional polyps and medusa buds. The Medusae break free of the polyp and swim away.
Major Classes
HydrozoaImage from: http://www.miramarbeachbum.com/jellyfish/
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ScyphozoaImage from:
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StaurozoaImage from:
http://www.marlin.ac.uk/phylumdetails.php?phylum=2353
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CubozoaImage from:
http://www.marlin.ac.uk/phylumdetails.php?phylum=2353 1. Tentacles hang from each of its corners. 2. Active swimmers and feeders in warm tropical waters. 3. Some possess dangerous nematoycsts. 4. Shaped like cubed jellyfish. |
AnthozoaImage from:
http://seanet.stanford.edu/Anthozoa/index.html 1. Colonial and lack medusae. 2.Their cnidocytes lack medusae. 3. Polyps differ in 3 ways: -mouth lead to a pharynx which leads to gastrovascular cavity. -Mesenteries (membranes) divide the gastrovascular cavity into sections. -the mesoglea contains amoeloid mesenchyme cells. 4. The polyp attaches to its substrate by a pedal disk. 5. Messenteries are arranged in pairs and attach at body wall at their outer margin. 6.Both monecious and diaecious. 7. Male gametes mature much faster. |