Echinoderms: Traits, Types & Roles

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  • 0:01 Echinoderms
  • 0:34 Traits
  • 1:51 Types
  • 4:00 Roles
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Instructor: Yuanxin (Amy) Yang Alcocer

Amy has a master's degree in secondary education and has taught math at a public charter high school.

After watching this lesson, you'll be well on your way to being an echinoderm expert! For example, you'll learn that sea cucumbers help clean up the ocean floor and that starfish can grow back any arms that are broken or damaged.

Echinoderms

This lesson is all about echinoderms. Echinoderms are animals that are of the phylum Echinodermata. Some examples of echinoderms include the sea star (aka starfish), the sea cucumber, and the sea urchin among others. This phylum has 6,000 species of marine life!

The word echinoderm has a Greek origin and literally means spiny skin, but this doesn't mean that all echinoderms have spines. Some sea cucumbers, for example, do not. Let's learn a little more about the traits of echinoderms.

Traits

The fact that all echinoderms are marine animals and do not live on land or in freshwater is one of the major traits of this group. Yes, all echinoderms live in the oceans with the majority living on the ocean floor.

Another major trait is that all echinoderms have radial symmetry. This means that just like a snowflake has a center point and grows from there, so do these marine animals. Look at a starfish, and you'll see its center point from which its arms grow. The center point of a sea cucumber is not as apparent, but if you look at a sea cucumber face on, you'll see that it is round and the animal gets bigger from this center. Sea urchins are round too and you can find its center point in the middle.

Another trait that echinoderms have is that the radial symmetry is a multiple of five. Sea cucumbers have have five rows of arms, so you it has a radial symmetry of five. Starfish usually have five arms, so they also have a radial symmetry of five. Some starfish have more arms because when one arm is damaged, the starfish can sometimes grow two in the place of the one lost arm.

Yet another trait common to this group of marine animals is that they have tube feet that are filled with sea water. If you flip a starfish over, you'll see hundreds of tiny tube feet.

Types

Within the phylum Echinodermata, there are 21 classes echinoderms. But only five of these classes are currently existing. All the others are extinct. The existing five classes are:

1. The Asteroidea (starfishes)

These starfishes have arms in multiples of five. You may have seen many starfish at a public aquarium with five arms. These animals can grow another arm if they lose one. They are also predators, crawling around on the ocean floor eating barnacles, mussels, snails, plankton, sea urchins, and even other starfish.

2. The Ophiuroideas (brittle stars)

Unlike starfishes, brittle stars have thin spindly arms. They move by wrapping their thin arms around other objects and pulling themselves. They are mostly scavengers, but also eat other worms and small crustaceans.

3. The Crinoideas (sea lilies)

This class also includes the feather stars. As adults, they attach themselves to the ocean floor. They have a mouth at the top of the stalk surrounded by feeding arms. These arms look like feathers and these animals as a whole look a lot like flowers with feathery petals.

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