The Brittle Starfish Essay, Research Paper

Marine Institute of Memorial University

“The Life of a Brittle Starfish”

Course: Biology 1100

Instructor: Keith Rideout

Due Date: November 3, 2000

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 the past. Fossil beds consisting almost exclusively of large numbers of one or a few species are known from as early as the Lower Cambrian. In present day these species including most echinoderms may cover large areas of the seafloor. The reason behind aggregation apparently is a response to one or more environmental factors, primarily food. Large numbers of ophiuroids including brittle star and crinoids occupy areas in which strong currents carry large amounts of plankton. A brittle starfish raises some of his arms in the water to capture the plankton and using the existing arms to hold on to other brittle stars. They do this so that they will not be swept away by the current.

4.0 Food Procurement

Brittle starfish obtain food by using its long arms to bring food to its mouth; the tube feet bring small particles of food to its mouth.

4.1 Place in the Food Chain

Some brittle starfish are scavengers, eating plant or animal material that they come across. Many of these species develop relationships with sponges or corals. They clean the host of debris and in return get a safe place to live. Some brittle starfish are predators as they catch shrimp, as they get older they catch bigger organisms such as squid and fish.

4.1 Food Source

Brittle stars eat many things. A brittle star’s diet can include barnacles, snails, sea urchins, clams and mussels. They also eat small animals and plankton. Many brittle stars eat mussels and clams. They also feed on detritus and small living or dead animals. After they get big enough they will in fact catch and eat fish hermits and condylactis anemones.

4.2 Predators

Predators known to consume a lot of brittle stars are bottom dwelling fish such as dab, American plaice, haddock and Norway lobsters. These predators do not generally consume the entire brittle star but get their arm as the brittle star will break off it’s own arm as a defense mechanism.

5.0 Evolution

Scientists speculate that the lack of Precambrian fossils of echinoderms indicate that in earlier years they lacked a calcite skeleton and thus did not fossilize. Ancient echinoderms exhibited a variety of bizarre body forms, the earliest forms seem to have been experimenting with different body forms and feeding mechanisms. They were adapted to life on hard or Soft Ocean floor and evolved the burrowing habit. Anatomy and paleontology studies suggest that they may have developed from a crinoidlike ancestor.

6.0 Conclusion

In conclusion the brittle starfish is a very unique organism, as it possesses the following characteristics:

 Will break off it’s own arms as a defense mechanism towards predators, the predator will eat the arm and the brittle starfish will regrow the arm.

 Has evolved over the years to develop a spinal chord.

 Some brittle starfish are predators and actually capture and eat the following shrimp, plankton, squid and fish.

 Has a water vascular system that consists of fluid-filled vessels that are pushed out from the body surface as tube feet, and other structures, which is used in sensory perception.

 Will aggregate in large numbers on coral, off fast moving current so that they can work as a team to capture plankton that gets swept through the current. One brittle star captures the plankton with a couple arms and uses the remaining arms to hold on to another brittle star so that it won’t be swept away.

Who would have thought that the brittle starfish could be so complex?

7.0 Pictures

7.1 Structures of The Brittle Star

7.2 Digestive System

7.3 Picture #1 of Brittle Starfish

7.4 Picture #2 of Brittle Starfish

Bibliography

1. “Introduction to the Asteroidea”*http://www.ucmp.berkeley.edu/echinodermata/asteroidea.html* (18 Oct 2000).

2. “The Ophiuroidea”. *http://home.att.net/~ophiuroid/home.html* (18 Oct 2000).

3. “Introduction to the Echinodermata”*http://www.ucmp.berkeley.edu/echinodermata/echinodermata.html* (18 Oct 2000).

4. “The Echinodermata”. *http://www.ldeo.columbia.edu/users/gregory/echinodermata.html* (18 Oct 2000).

5. “Brittle Star”. *http://lycoskids.infoplease.com/ce5/CE007562.html* (23 Oct 2000).

6. “The Ophiuroidea”. *http://www.ucmp.berkeley.edu/echinodermata/ophiuroidea.html* (23 Oct 2000).

7. “The Brittle Star”.*http://lycos.infoplease.com/ce5/CE007562.html* (23 Oct 2000)