Echinoderms – BR

BR’s writing is really improving.  He went back several times to add new information or clean up his rough thoughts.


Echinoderms are a group of marine animals.  Their name comes from the Greek meaning “spiney” “skin”.    Echinoderms are split into three main orders that do not look alike.  They reproduce by sperm and egg.  Their mouths and tube feet are on the oral (bottom) of the body and the anus is on the aboral (top) of the body.  They have tube feet.  To use the tube feet, they suck in water and push it out madrephorea. They have eyes on each of their appendages.

Sea cucumbers look a good bit like sea slugs but are not.  They are in the phylum Echinodermata and class Holothurian.  Sea cumbers are not like any other echinoderm.  They have no arms or hard spines.   All sides of the sea cucumber do not look alike. They have a ring of feeding tentacles which are highly modified tuber feet. They use them to push in food. When the sea cucumber is scared they squirt out their intestines for a defense mechanism. Sea cumbers can not swim and are benthic. They are edible and are a common food in Spain.

Sea urchins are in the phylum Echinodermata and class Echinoida.  The life cycle of a sea urchin starts with an egg then progresses to the aechinoplutes (larval stage) and then they go through a metamorphosis and finally an adult sea urchin.  They eat using a structure called Aristotle’s lantern. It is located in a sea urchin’s mouth.  In Aristotle’s lantern is a set of five teeth that come together.  The teeth are very strong so they can scrape off alga from rocks.

Sand dollars are flat cousins of sea urchins. When the sand dollar is alive, it is covered in short spines. When the sand dollar is dead and sun bleached, it is smooth and grey or white. Their short spines help them burrow into the sand. They only live on sandy bottoms so they a place for protection from waves and predators and a way to obtain food. The sand dollar burrows, while digging tiny food particles fall between their spines and then cilia and tube feet drag it to the mouth.

Sea stars are not “fish”, so the name star fish is a misnomer. The proper name is sea star. They are in phylum Echinodermata and class Asteroidia.   Sea stars come in all shapes and sizes.  The largest starfish can be over four feet in diameter and the heaviest weighs over 13 pounds. Starfish can have between five and ten legs. They use their tube feet to burrow into the sand to find food.  Small clams are what they prefer.

Brittle stars are in phylum Echinodermata and class Ophiuroida. The life cycle of a brittle star begins with an egg and progresses to an ophoipluteus (larve).  Then they go through metamorphosis and an adult brittle star appears.  They live on jetties and rocks.  They shun daylight. To hide they go under seaweed, rocks and other dark places. They also find food in those places.  They have a really effective defense mechanism.  They can make their arm fall off for their predator to eat while the brittle star gets away.  It then grows back its arm.

Even though the Echinoderms seem very diverse, there are numerous similarities. All echinoderms are marine meaning there are no fresh water species and only a few can live in brackish water.  All Echinoderms are radially symmetrical.  This means you can cut them apart and they will grow a new whole creature from each cut up creature. They will eat anything and are opportunistic eaters.  They help the ocean to be clean.


1 Comment

Filed under Biology, BR, Science

One response to “Echinoderms – BR

  1. lapazfarm

    Excellent essay, BR! Lots of interesting detail and very well-written!

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