The brittle starfish

Marine Institute of Memorial University

“The Life of a Brittle Starfish”

Course: Biology 1100
Instructor: Keith Rideout
Due Date: November 3, 2000

Presented By: Joe MacDonald
Student #: 961687

Table of Contents

Page #
1.0 Introduction 1

2.0 General features 1-2
2.1 Stereom 2
2.2 Water Vascular System 2

3.0 Habitat 3
3.1 Aggregation 3

4.0 Food Procurement 3-4
4.1 Food Source 3
4.2 Predators 4

5.0 Evolution 4

6.0 Conclusion 4

7.0 Pictures 5-9
7.1 Structures of Brittle Starfish 5
7.2 Digestive System 6
7.3 Picture #1 of Brittle Starfish 6
7.4 Picture #2 of Brittle Starfish 7

Bibliography 8

1.0 Introduction

The type of marine organism, which will be reported on within the following text, is the Brittle Stars. The Brittle Star is also called the serpent star and a common name for a large group of echinoderms closely related to the starfish. These organisms make up the class Ophiuroidea; another common name for ophiuroidea is snake stars. These organisms can be found in all oceans but are more abundant in the Tropics. Brittle stars can come in different colors.

2.0 General Features

Their bodies have a central disk that is demarcated from five arms, unlike true starfish. Their five arms can be broken off quite easily, but will regenerate themselves. These arms are usually forked and spiny. The brittle star includes about 2000 species, and the arms are about 20 cm in length. The central disk is about 1 inch across. Unlike the traditional starfish which uses tube feet to crawl and attach itself to objects. The brittle starfish uses his tube feet to breathe and to bring food to it’s mouth, they do not use the tube feet as a suction mechanism. The brittle starfish moves their arms to swim and crawl. The brittle starfish contains a mouth on the underside of its body and their tube feet are mainly used as sense organs for detecting light and odor. The most common type of brittle star is the long-armed type, which is a grayish or bluish species that is luminescent. Brittle stars with many branched arms are called basket stars. Some brittle stars may reproduce by breaking across the middle of the body disk, with each of the halves growing it’s missing half and corresponding arms. Brittle stars lack open groves on the lower surface of their arms. Each arm contains a series of jointed bonelike plates, or ossicles, which determine the freedom of arm movements. They can move in any direction and very quickly. They also have a skeleton composed of numerous plates of calcium carbonate.

2.1 Stereom

The plates that compose brittle starfish, ophiuroids and echinoderms is calcite along with other organics. Though each plate is a single crystal of calcite, it doesn’t take a typical crystalline form. Below is a picture of the tooth socket, notice the holes.

2.2 Water Vascular System

Perhaps not as obvious is the water vascular system, another trait common to all echinoderms. By examining the oral underside side of a brittle star, one will be able to see hundreds of tiny feet usually arranged into several rows on each appendage of the star. These are the tube feet, or podia, and are filled with seawater in brittle stars. The water vascular system within the body of this species is also filled with seawater. By expanding and contracting chambers within the water vascular system, the brittle star can force water into certain tube feet to extend them. The animal has muscles in the tube feet, which are used to retract them. By expanding and retracting the right tube feet in the proper order, the creature can walk. Many echinoderms can also form suckers on the ends of their tube feet. These suckers can be used to capture and hold prey, or to hold onto rocks in a swift current or tide.

3.0 Habitat

Brittle stars can be found in the warmest and coldest of the world’s seas and have a broad geographic range. Brittle stars can be found at various depths of the ocean and tend to cling to rocks for concealment. They cannot be found on land or fresh water. These organisms are not often seen because they live under rocks or in coral, seaweed and they burrow into the mud or sand.

3.1 Aggregation

These marine organisms tend to aggregate in large numbers and evidently also did so in