Phylum Echinodermata

Body Structure

I10-82-starfish.jpg Echinoderms are a group of animals that include starfish,urchins,feather stars,and sea cucumbers.In spite of their potentially misleading name, the echinoderms do not possess an external skeleton. Instead, they have a outermost layer of thin, and spiny skin. Echinoderm means "spiny skin". Echinoderms are the only animals that have lots of tiny tube like structures called tube feet. The Echinoderms body parts are all arranged around the center of the animal. Echinoderms bodies are usually divided into five parts with the animals mouth in the middle. All Echinoderms have an internal body skeleton. Echinoderms aren't fish because they do not have fins, or a vertebrae. On the sea star, under it's arm are thousands of little feet which are the tube feet. Those feet are a huge help in the Echinoderms life. Their body structure is like a wheel, or radial symmetry. They have no brain, heart or eyes, and their mouth is on the bottom side and their anus is on the top. Echinoderms do have very highly developed sensory organs, such as an eyespot that senses light.

Obtaining Food

Most echinoderms are filter feeders, grazing on the bottom of the ocean, or climbing on rocks and eating the dirt off of that rock. Echinoderms use tube feet to obtain food. Echinoderms are the kind of species that sits and waits for their food. Once the food comes in the current, their tube feet quickly send the food to the middle of the Echinoderm to be digested. Echinoderms' tube feet are connected to a very unique water vascular system. The water vascular system in an echinoderm is a hydraulic system that inflates with sea water. That water vascular system helps them obtain food and it helps them move as well. Echinoderms graze on top of rocks and they scrape off thin layers of nutrients. Echinoderms often digest their food by turning their stomach outside their body. They will locate the food source and then eject their stomach around it to begin digestion.

Purple Sea Urchin

Echinoderms use sexual intercourse for reproduction. In some species egg and sperm cells are released into open water for fertilization. They have to have two parents to make a baby. Echinoderms reproduce by laying eggs that turn into larva that swim freely.
Echinoderms not only reproduce by sexual reproduction, but also by asexual reproduction. This process is called regeneration. It may not be intended, but when seastars lose arms, the seastar that lost the arm can regrow the arm, while the arm grows a new body. Sea Urchins spines come off unintentionally, but are replaceable.


Echinoderms use tube feet to move as well. They use those feet to attach to rocks. They also use those feet to protect themselves. Because the echinoderms have tube feet they have a limited speed and movement. Each ray of a sea star has an eyespot. Though it cannot see as well as we humans can but it can detect light and the direction it is going. they use the eyespot so they have some general idea of where they are going. The movement of echinoderms are slow, but it pays off.


Echinoderms can grow back limbs if they fall off, called regeneration. For example, if a predator bites off an arm of a sea star, that sea star can grow back its arm. Sea Stars can come in many colors, depending on the environment the can change into these colors purple to red, pink, brown, orange, and yellow.

Importance to Humans

Leopard Sea Cucumber
Sea cucumbers are a part of the species called Echinoderms. Sea cucumbers clean up the poop of other sea creatures. If the sea cucumber didn't clean up the poop on the ocean floor, there would be piles and piles of poop just sitting there. After a while, fish would die because poop would be everywhere. They could not even breathe without taking in poop. That is just one of the many important reasons that echinoderms are important in our life.