Unit 8: Invertebrates                                                    1   2   3   4   5   6

6. Echinoderms

a) Habitat

     All the animals included in this group are aquatic and marines.

     They live on the sea bed, some fixed to substrate

     and others move slowly about.

b) Morphological characteristics

- They have radial symmetry.

-   Their body can have several shapes and it is formed by five equal sections.

-   They have an internal skeleton (under the skin) made of plaques of calcium

   carbonate, called dermal skeleton. Usually they have spines too.

-   They do not have a differentiated head.

c) Vital functions

     Nutrition:

The digestive system has mouth, anus and glands. They are carnivorous.

They have an exclusive system called ambulacral apparatus.

It consists on a series of tubules filled with sea water

that end in ambulacral feet with suckers. It has several functions: locomotion, breathing, circulation and excretion.

Interaction:

They do not have a well-developed nervous system: neither brain nor complex sense organs.

Reproduction:

They have sexual reproduction. Most have separated sexes and some are hermaphrodites.

Fertilization is external.

They are oviparous.

Larva hatches and undergoes metamorphosis to change into adult. 

Some species have regeneration power. This is the capacity to develop again lost body parts.

d) Classification

6.1. Answer the following questions about Echinoderms:

a. What is the dermal skeleton? What is it made up? Where is it located?

b. What is the ambulacral apparatus? What are its functions?

6.2. There are five groups of Echinoderms. Can you identify them

        among the pictures?

6.3. Listen and indicate which characteristic of Echinoderms is described: