phylum echinodermata sea star, sea urchin, sea cucumber

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Phylum EchinodermataSea Star, Sea Urchin, Sea Cucumber

General CharacteristicsSpiny skinnedpentaradial symmetry = as adults have five similar parts arranged in circle around a central pointexclusively marine, adapted to a bottom-dwelling existenceexamples include sea stars (starfish), sea urchins, sand dollars, sea cucumbers

most species reproduce sexually, have separate sexes, and have external fertilization. Note that the larvae of echinoderms are ciliated and bilaterally symmetric .

Many echinoderms are recognized by theirpentaradial(five-fold)symmetry. It is important to understand that the radial symmetry of echinoderms is superficial and almost certainly secondarily derived. This means that the ancestor of echinoderms (the ancestor it shares in common with all other bilaterians) was likely bilaterally symmetric. If we look carefully at a typical echinoderm like the sea star we will note that the five part organization can be divided into mirror-image right and left halves - the hallmark of bilateral symmetry. An easy way to see this is to find the madreporite and imagine a line connecting it to the tip of the arm opposite the madreporite. This line will divide the animal into right and left halves.

Muscular/ Skeletal SystemMouth on the bottom side of organism (oral surface). Other side= aboral surfacehave an internal skeleton (endoskeleton) composed of interlocking calcium carbonate plates

Water Vascular SystemContains a water vascular systemWater enters body through a sieve plate (=madreporite) The water is transport through the ring canal and the radial canal to power the tube feethave tube feet, which are versatile structures used for locomotion, gas exchange, feeding, attachment, and sensory reception!Tube feet:..\..\..\Lesson Videos\Biology 11\Arthropods and Echinoderms\Starfish or Sea Star (Asteroidea).flv

DigestionUse tube feet to open bivalves, to capture preysSea stars and sea urchins contain pedicellaria = grasping appendages

(food gathering, cleaning, & defense against predators)Sea stars can flip its stomach out of the mouth and digest/ eat the food outside its body. It will flip its stomach back in when finished.

Herbivores (e.g. sea urchins) have 5-part jaws to scrape algaeSome are filter feeders (sea lillies, brittle stars)Some detritus feeders

RespirationDiffusion through tube feet

CirculatoryDone by digestive gland and fluid in body (located in pseudocoelem)

ExcretorySolid food waste anusNitrogen waste tube feet, gill, all over body

Nervous SystemNo brain (radial symmetry)Nerve rings around mouth; eyespot; statocysts

MovementUse tube feet

ReproductionEchinoderm sexes are generally separate Fertilization and development of young are external, larval stage in life cycleClass Asteroida (Sea Stars)5-26 armseyespots located on tip of each armpush stomachs out of body through mouth to devour preycan regenerate lost or damaged arm, but is very slowgills protrude through skin

Crown of thorns starfishReading and species file

Video:..\..\..\Lesson Videos\Biology 11\Arthropods and Echinoderms\Crown-of-Thorns starfish.flv

Know your anatomyWorksheet time


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