A sea cucumber (Actinopyga echinites), displaying its feeding tentacles and tube feet


Echinoderms come from the words echinos and derma. Echinos means thorn, derma means skin. Thus, echinoderms are animals that have spines on their skin. Live in marine habitats. The outside of the body is very hard, composed of lime / chitin. It has five arms radially and symmetrically.

Has the ability autotomy, namely the ability to cut off a body part (usually the arm) if it feels threatened and can grow it back into its original shape. Including triploblastic coelomate animals, which have a true body cavity composed of 3 layers of tissue, namely ectoderm, mesoderm, and endoderm.

The movement of Echinoderms uses an amburacral system, namely arm movements occur due to changes in water pressure in the water vessel system. In addition to moving, the amburacral system in echinoderms is also used to catch prey and breathe. The following is the mechanism of movement of the amburacral system carried out by Echinoderms:

  1. At the top of the body of Echinoderms there is a hole called the madreporite which is equipped with a filter (pore).
  2. The water enters the madreporite hole into the ring channel and will be dispersed into the tube foot radial channel
  3. Water is sprayed on the tube feet to create hydraulic pressure so the tube feet can stick out.
  4. This causes the ampulla to attach to other substrates and allows Echinoderms to move and move.

The digestive system consists of the mouth (below the body), esophagus, stomach, intestines, and anus (located above the body). The nervous system consists of a ring of nerves that surrounds the mouth and has 5 branches on each arm. The sexes are separated and reproduction is done by external fertilization (fertilization occurs outside the body).

After fertilization occurs, a zygote will form and develop into ciliated larvae (bipinnaria) that can swim and become adults if they are in a suitable habitat.

Classification, Body Structure, and Examples of Echinoderms

Based on their characteristics, Phylum Echinoderms are divided into 5 classes, namely:

1. Asteroidea (starfish)

Body shape like a star. Lives in coastal habitats. It has five short, blunt spiked arms on the surface of its body. The locomotion is an ambulacral leg. The body is divided into the oral side or the lower side (where the mouth) and the aboral side or the upper side (where the anus).

The outermost surface layer is composed of a layer of ciliated epidermal cells and has an endoskeleton underneath. Examples of Asteroidea are Culcita (skinned starfish), Linkia laevigata (blue starfish), Pentaceros (horned starfish), Astrias vulgaris (large starfish), and Ctenodiscus (mud starfish).

Astrias vulgaris
Astrias vulgaris
Image source: gulfofme.com

2. Ophiuroidea

Often referred to as the snake star because it has long arms and moves like a snake. Its habitat is in deep and shallow sea waters, especially behind rocks or buried in sand. Has a madreporite which is located on the bottom (mouth) and does not have an anus, so that the rest of the food is expelled through the mouth. Examples of Ophiuroidea are Ophiothrix fragillis and Ophiopholis aculeata.

Micro brittle starfish and Caulerpa racemosa
Micro brittle starfish and Caulerpa racemosa

3. Crinoid

Shaped like a lily (sea lilies) and has five forked arms. Its life attaches to the substrate and forms colonies so that it looks like a marine garden. Under unfavorable conditions, Crinoidea will escape from the substrate and move to another place. Lacking madreporite, mouth and anus are located in the oral cavity. In the aboral there is a calyx, which is a chalk slab shaped like a cup. An example of Crinoidea is Antedon sp. and Holopus sp.

Crinoid on the reef of Batu Moncho Island, Indonesia
Crinoid on the reef of Batu Moncho Island, Indonesia

4. Echinoidea

Often referred to as sea urchins. Lives in sand and rocks. It has no arms, is circular in shape, slightly flattened, and the body surface is surrounded by many spines. The mouth and 5 teeth are in the oral part, while the anus, genital opening, and are in the aboral part. Examples of Echinoidea are Diadema saxsatile (sea urchins) and Echinothrix sp. (sea urchin).

Tripneustes ventricosus and Echinometra viridis
Echinometra viridis

5. Holothuroidea

Often referred to as sea cucumber. Lives in sand or lime. It has a soft body, smooth spines, and is shaped like an elongated sac. The mouth is anterior, while the anus is posterior. Examples of Holothuroidea are Holothuria scabra, and Thyone byereus (sea cucumber).

A sea cucumber (Actinopyga echinites), displaying its feeding tentacles and tube feet
A sea cucumber (Actinopyga echinites), displaying its feeding tentacles and tube feet

Echinoderms Reproduction

Echinoderms reproduce both sexually and asexually. Sexually, by external fertilization (fertilization is outside the body of the parent) and produces bilaterally symmetrical larvae that attach to the substrate to grow into new echinoderms. Asexually, namely by dividing body parts or fragmentation and regeneration of lost body parts.

Related Post

Gravatar Image
Student Biology Major, Universitas Gadjah Mada. Focus on ecology and enviromental.