6.+Echinodermata

Above is an example of a species of echinodermata, a star fish.


 * 1. Classification/Diagnostic characteristics**

Echinodermata show radial symmetry; their body parts are arranged around a single axis at the center so that it could be divided into smaller halves by any plane containing the central axis. These organisms include sea stars, sea urchins, and their relatives. They have an endoskeleton, i.e, the skeleton is enclosed by the epidermis.Tube feet called podia are present and they have a coelom, large gonads, and a gut (A coelom is an open, fluid-filled body cavity).They also have poorly developed nervous and sensory systems.


 * 2. Relationship to humans**

- Research on echinoderms has contributed to the overall knowledge of animal fertilization and development. - Sea urchin eggs are also edible. - Raw or cooked sea urchin or echinoderm gonads are considered a delicacy in some countries - Holothurin, a toxin created by some kinds of echinoderms is used by Pacific Islanders to kill fish - The Holothurin toxin is not harmful to humans and has actually been found to stunt tumor growth, making it potentially beneficially in cancer studies - Some echinoderms are pests in marine environments because they feed on commercially useful mollusks, oyster beds, and young seaweed plants that could be used by humans


 * 3. Habitat and niche**

Echinodermata are marine animals which can be found in almost any sea or ocean. - Echinoderms can be found in many depths of the ocean, and a select few can be found in __brackish waters__, which are bodies of water on land with a higher salt concentration than freshwater (Animal Diversity Web)


 * 4. Predator avoidance**

- They are most vulnerable in their larval stage - Have an adaption so when they lose an arm, it regenerates - Have an adaption to shoot sticky tubes (cuvierian tubes) at any attacker - Their main predator is the otter [|Cuvierian tubules]


 * 5. Nutrient acquisition**

Echinoderms have a water vascular system which they use for gas exchange, movement, and feeding. In addition, they have flexible feet which they use to catch prey. Many are suspension feeders, herbivores, detritivores, and predators. (1) Starfish have hundreds of sticky legs, which are used to grasp food and eat it.


 * 6. Reproduction and life cycle**

- They are mainly gonochoristic (have separate sexes) (1) - Echinoderms have reproductive strategies that vary from free spawning and indirect development to brooding and direct development. (1) - Spawning is a nocturnal event. (1) - They typically do external fertilization where eggs and sperm are freely discharged into the water. (2)

Echinoderms have amazing regeneration abilities. Some species will actually reproduce when an arm pulls away from the starfish and regenerates into a new individual. Starfish can use self amputation, or autonomy, as a form of asexual reproduction. They can also use fission - the process of breaking into unequal parts to reproduce with the donor starfish regenerating limbs lost during fission.

After an egg is fertilized, if the egg is a small egg without much yolk, it'll develop into free-swimming larvae that become part of the plankton, feeding on smaller organisms until they transform and begin life on the seafloor. If the egg is larger with greater amounts of yolk, it'll develop into a larval form that is planktonic but supports itself using its yolk material until transforming into a juvenile echinoderm. ([])


 * 7. Growth and development**

Echinoderms are deuterostomes. They have a system of calcified internal plates which are covered in skin and muscle. These thick calcified plates form an internal skeleton. They have a stomach and digestive glands and an anus that is separate from their mouths. As larvae, they use their cilia to move through the water. Echinoderms have bilateral symmetry when they are young, but develop pentaradial symmetry, or symmetry in multiples of five, as they grow older. In addition, this type of development allows the organism to move slowly in all directions.

Question: How might having calcified internal plates protect an star fish from predators?

Answer: The calcified internal plates which rest under a surface of muscle and skin makes it harder for a predator to penetrate and consume it.


 * 8. Integument**

Echinodermata has a mesodermal skeleton. It is made of calcerous plates. Its cells are secrete sticky materials or toxic fluids. Change color to hide from predators.




 * 9. Movement**

Most cannot move, i.e, they are sessile. Some are able to swim or float. They can use their tube feet or spines to move. The tube feet have suction pads which create a vacuum with the contraction of muscles. Starfish contain hundreds of little tube feet, which are used to "walk around," and attach to rocks. This also allows starfish to grab onto prey.

media type="youtube" key="QBGccVAfJV4" width="334" height="189"

The above video displays how the starfish actually seems to be just "slipping" along the sea floor. Such demonstrates the ancillary actions of those little feet under the starfish to propel it along in efforts of foraging.


 * 10. Sensing the environment**

There is no brain, but the nervous system has nerves running from the mouth to arms. There are tiny eyespots along the arms that detect light and dark. Some of the feet can feel chemicals, this allows them to spot food using smell or other indicators.

Question: Would a star fish be an ideal model of the human nervous system?

Answer: Unlike C.elegans, the nervous system of a star fish is very different than that of a human. Our nervous system, unlike the star fish, is centralized in the spinal cord and brain.


 * 11. Gas Exchange**

Echinoderms have a circulatory system that consist of a multitude of fluid filled channels that assist in gas exchange, nutrient acquisition, and movement. Echinoderms contain an under developed respiratory system which includes simple gills. The fluid filled channels contain flexible tube feet, which inspire oxygen and expire carbon dioxide.

Question: How do echinoderms perform respiration in a way that is similar to the way that humans perform respiration?

Answer: Like humans, echinodermata, specifically star fish, perform gas exchange through channels in a way that is similar to the gas exchange that occurs in the lungs, veins, and capillaries of humans.


 * 12. Waste removal**

Echinoderms have an extremely simple excretory system that does not consist of any kidneys. Their main source of waste is ammonia gas, and they get rid of this by simple diffusion.


 * 13. Environmental physiology (temperature, water, and salt regulation)**

Echinoderms are highly susceptible to changes in light, salinity and temperature and respond to these environmental factors by feeding at night and seeking well-regulated environments. Salinity is very important to echinoderms as they are marine animals and only a couple of species being able to survive in brackish water. Despite this, they are found throughout a broad array of different marine environments both cold and warm and have adapted to cover most of the world's marine habitats.

Question: How are these organisms well-adapted to their environments?

Answer: By feeding at different times, specifically during the night, these organisms have easily avoided a main concern for themselves.

Question: Why might have they not developed adaptations to better acclimate to their environment?

Answer: The need for an adaptation was not present because their concerns in terms of environment and temperature could easily be avoided by changing their behavior. Essentially, the need for a physical adaptation was not necessary.


 * 14. Internal circulation**

Echinoderms do not have a true heart, and their circulatory system often does not contain blood with the respiratory pigment.


 * 15. Chemical control (i.e. endocrine system)**

Most species have gonads which produce hormones related to reproduction in addition to other functions. [|Source]


 * Sources**

http://animaldiversity.org/accounts/Echinodermata/ (1)

http://www.ucmp.berkeley.edu/echinodermata/echinolh.html (2)

“Echnioderms.” //Echinoderms //, 10 Nov. 2017, www.mesa.edu.au/echinoderms/.

http://www.ucmp.berkeley.edu/echinodermata/echinolh.html

http://animaldiversity.org/accounts/Echinodermata/

http://www.mesa.edu.au/echinoderms/

[]

https://en.wikipedia.org/wiki/Echinoderm

https://lh3.googleusercontent.com/-2qbNn7hIk2M/Vo_y49eDPeI/AAAAAAAAEuk/oJMxep2pM2E/Echinodermata-star%252520fish%25255B8%25255D.jpg?imgmax=800

https://xavierendocrinesystem.weebly.com/echinodermata.html

http://www.starfish.ch/reef/echinoderms.html

http://phenomena.nationalgeographic.com/2012/01/17/starfish-go-five-ways-but-two-ways-when-stressed/

http://www.madreporite.com/science/movement.htm