Echinoderms
"Echinoderm" is Latin for "spiny skin". This phylum includes sea stars, sea urchins, sea lillies, sea cucumbers, sand dollars and sea biscuits. There are approximately 7,000 species that make up the Echinoderms.
General Information
This system is composed of tubes, canals and valves of water that are used for moving and feeding. The tube feet will extend when filled with water and often have suckers on the end to aid in feeding, movement, and holding on to the substrate.
Digestive System
Echinoderms are primarily carnivorous. In order to feed, the stomach is extending inside out thru the mouth. It secretes digestive enzymes and carries the food back into mouth. The gut ranges in size from very short (starfish or sea cucumbers) to very long (sea urchins). Longer guts are used to digest plant particles. Nutrients are transported in coelomic fluid that is found in the coelom. Waste is excreted thru the anus.
Circulatory System
Echinoderms lack a true circulatory system so oxygen is transported via the coelomic fluid. Gas exchange (O2 & CO2) occurs in small, branched projects of the body wall that are connected to the coelomic cavity. Sea cucumbers are a bit different; they have respiratory trees. These are a pair of thin, branched tubes that are extensions of the gut and are suspended in the coelomic fluid. They draw in water and provide increased surface area for gas exchange.
Nervous System
There is not a lot of information on the echinoderm nervous system. They don't have a brain (remember--no head!) but they do have a nerve net like the Cnidarians. This coordinates the tube feet and spine movement. It also allows the organism to right itself if turned over. In sea urchins, it is responsible for camouflage.
Reproductive System
Echinoderms are dioecious (different genders). They may have as many as 5-10 gonads located in their body cavity. In order to better ensure fertilization, all species will spawn at once by releasing eggs and sperm into the water. The fertilized egg developes into plankton as a bilaterally symmetrical, ciliated larva. Some species keep fertilized eggs in pouches or underneath the body. Reproduction can occur asexually by regeneration--the ability to grow back lost/damaged parts. This can only occur if a portion of the central disk is included in the cut part.
- Echinoderms can be found in almost all benthic marine areas from shallow intertidal pools to the depths of the ocean.
- Larvae are free-swimming with bilateral symmetry. As larvae grows, the left side overtakes the right side and grow in a 5-sided radially symmetric pattern.
- Variety of colors
- Have no head
- No anterior or posterior side, instead oral and aboral
- Complete digestive tract
- Internal endoskeleton that is secreted w/in tissues. It may be covered by a thin layer of ciliated tissues.
- Coelomates
- Contain a water vascular system
This system is composed of tubes, canals and valves of water that are used for moving and feeding. The tube feet will extend when filled with water and often have suckers on the end to aid in feeding, movement, and holding on to the substrate.
Digestive System
Echinoderms are primarily carnivorous. In order to feed, the stomach is extending inside out thru the mouth. It secretes digestive enzymes and carries the food back into mouth. The gut ranges in size from very short (starfish or sea cucumbers) to very long (sea urchins). Longer guts are used to digest plant particles. Nutrients are transported in coelomic fluid that is found in the coelom. Waste is excreted thru the anus.
Circulatory System
Echinoderms lack a true circulatory system so oxygen is transported via the coelomic fluid. Gas exchange (O2 & CO2) occurs in small, branched projects of the body wall that are connected to the coelomic cavity. Sea cucumbers are a bit different; they have respiratory trees. These are a pair of thin, branched tubes that are extensions of the gut and are suspended in the coelomic fluid. They draw in water and provide increased surface area for gas exchange.
Nervous System
There is not a lot of information on the echinoderm nervous system. They don't have a brain (remember--no head!) but they do have a nerve net like the Cnidarians. This coordinates the tube feet and spine movement. It also allows the organism to right itself if turned over. In sea urchins, it is responsible for camouflage.
Reproductive System
Echinoderms are dioecious (different genders). They may have as many as 5-10 gonads located in their body cavity. In order to better ensure fertilization, all species will spawn at once by releasing eggs and sperm into the water. The fertilized egg developes into plankton as a bilaterally symmetrical, ciliated larva. Some species keep fertilized eggs in pouches or underneath the body. Reproduction can occur asexually by regeneration--the ability to grow back lost/damaged parts. This can only occur if a portion of the central disk is included in the cut part.
Class Asteroidea
- Sea stars, also known as starfish
- 5 arms radiating from a central disk with an eyespot at each end that is light-sensitive
- Hundreds of tube feet with suckers that protude from oral surface along ambulacral groove
- Move in any direction very slowly
- Calcium carbonate endoskeleton
- Eat bivalves, snails, barnacles
- have pedicellariae = modified spines that are pincer-like organs, these are used to clean the surface
Class Ophiuroidea
- Brittle stars
- 2000 species
- very long and flexible arms
- arms move in snake-like motion for locomotion (most mobile echinoderm!)
- tube feet have no suckers and are used for feeding
- feed on organic matter and small animals picked up from the bottom, most are scavengers
- hide under rocks, coral, or cover up with mud/sand; they don't like lots of light
Class Echinoidea
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Class Holothiuroidea
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Class Crinoidea
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