Book contents
- Frontmatter
- Contents
- List of boxes
- Preface
- Acknowledgements
- Illustration acknowledgements
- Chapter 1 The process of evolution: natural selection
- Chapter 2 The pattern of evolution: methods of investigation
- Chapter 3 Porifera
- Chapter 4 Cnidaria
- Chapter 5 On being a worm
- Chapter 6 Platyhelminthes and Acoelomorpha
- Chapter 7 Nemertea
- Chapter 8 Nematoda
- Chapter 9 Annelida
- Chapter 10 Mollusca: general and Gastropoda
- Chapter 11 Mollusca: Bivalvia and Cephalopoda
- Chapter 12 Arthropoda: general
- Chapter 13 Crustacea
- Chapter 14 Chelicerata and Myriapoda
- Chapter 15 Insecta
- Chapter 16 Animals with lophophores
- Chapter 17 Echinodermata
- Chapter 18 Invertebrate Chordata and Hemichordata
- Chapter 19 Development
- Chapter 20 Invertebrate evolutionary history
- Further reading
- Glossary
- Index
Chapter 17 - Echinodermata
Published online by Cambridge University Press: 05 September 2012
- Frontmatter
- Contents
- List of boxes
- Preface
- Acknowledgements
- Illustration acknowledgements
- Chapter 1 The process of evolution: natural selection
- Chapter 2 The pattern of evolution: methods of investigation
- Chapter 3 Porifera
- Chapter 4 Cnidaria
- Chapter 5 On being a worm
- Chapter 6 Platyhelminthes and Acoelomorpha
- Chapter 7 Nemertea
- Chapter 8 Nematoda
- Chapter 9 Annelida
- Chapter 10 Mollusca: general and Gastropoda
- Chapter 11 Mollusca: Bivalvia and Cephalopoda
- Chapter 12 Arthropoda: general
- Chapter 13 Crustacea
- Chapter 14 Chelicerata and Myriapoda
- Chapter 15 Insecta
- Chapter 16 Animals with lophophores
- Chapter 17 Echinodermata
- Chapter 18 Invertebrate Chordata and Hemichordata
- Chapter 19 Development
- Chapter 20 Invertebrate evolutionary history
- Further reading
- Glossary
- Index
Summary
Echinoderms include starfish, brittle stars, sea urchins, sea cucumbers, sea lilies and feather stars. They are very unusual animals. They are radially symmetrical with no head end, yet are far more complex than the cnidarians in that they have three cell layers and a coelom, and most can form a temporary brain that coordinates locomotion. Their size varies: starfish range from 10 mm to 1 metre in diameter, and some sea cucumbers are as much as 2 metres in length. About 7000 species have been described, all marine. While the number of species is not very great, echinoderms are extremely numerous as individuals in unpolluted seas and deep water. This is a successful and very interesting phylum.
The echinoderm body plan is not only unusual, it has some features unique among animals. Discussion of these features, and an indication of the directions of evolution that have occurred, is followed by an account of the larval forms. Unlike the invertebrate phyla so far introduced, echinoderms are deuterostomes; unlike the soft-bodied invertebrates, the evolutionary history of the phylum can be traced by a well-marked sequence of fossils. Their evolutionary history is outlined in Chapter 20.
What is unique about echinoderms?
The water vascular system
The echinoderm water vascular system has a central coelomic cavity that transports sea water within the animal and bears the tube feet, thin-walled extensions of the epidermis lined with mesoderm and connected with the radial canals.
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- Information
- An Introduction to the Invertebrates , pp. 222 - 235Publisher: Cambridge University PressPrint publication year: 2006