Download Invertebrate Classification

Invertebrate Classification
Douglas Wilkin, Ph.D.
Jean Brainard, Ph.D.
Say Thanks to the Authors
Click http://www.ck12.org/saythanks
(No sign in required)
To access a customizable version of this book, as well as other
interactive content, visit www.ck12.org
CK-12 Foundation is a non-profit organization with a mission to
reduce the cost of textbook materials for the K-12 market both
in the U.S. and worldwide. Using an open-content, web-based
collaborative model termed the FlexBook®, CK-12 intends to
pioneer the generation and distribution of high-quality educational
content that will serve both as core text as well as provide an
adaptive environment for learning, powered through the FlexBook
Platform®.
Copyright © 2012 CK-12 Foundation, www.ck12.org
The names “CK-12” and “CK12” and associated logos and the
terms “FlexBook®” and “FlexBook Platform®” (collectively
“CK-12 Marks”) are trademarks and service marks of CK-12
Foundation and are protected by federal, state, and international
laws.
Any form of reproduction of this book in any format or medium,
in whole or in sections must include the referral attribution link
http://www.ck12.org/saythanks (placed in a visible location) in
addition to the following terms.
Except as otherwise noted, all CK-12 Content (including
CK-12 Curriculum Material) is made available to Users
in accordance with the Creative Commons Attribution/NonCommercial/Share Alike 3.0 Unported (CC BY-NC-SA) License
(http://creativecommons.org/licenses/by-nc-sa/3.0/), as amended
and updated by Creative Commons from time to time (the “CC
License”), which is incorporated herein by this reference.
Complete terms can be found at http://www.ck12.org/terms.
Printed: October 23, 2012
AUTHORS
Douglas Wilkin, Ph.D.
Jean Brainard, Ph.D.
www.ck12.org
C ONCEPT
Concept 1. Invertebrate Classification
1
Invertebrate Classification
• Give an overview of invertebrate classification.
Invertebrate, arthropod or insect?
This Monarch caterpillar is an invertebrate. It is also an insect and an arthropod. Of all the animal species, it is
estimated that well over 90% are invertebrates. Of all invertebrates, the insects are by far the most numerous. There
are so many species of insects that scientists have yet to discover them all, let alone name or count them. Estimates
of the total number of insect species fall in the range of 1 to 30 million. So, it helps if there are methods to classify
not just the insects, but all invertebrates.
Classification of Invertebrates
Eight major phyla contain the majority of invertebrate species.
Major Invertebrate Phyla
Table 1.1 gives an overview of the eight invertebrate phyla with the greatest number of species.
TABLE 1.1: Major Invertebrate Phyla
Phylum (includes)
Porifera (sponges)
Cnidaria (jellyfish, corals)
Platyhelminthes (flatworms, tapeworms, flukes)
Nematoda (roundworms)
Mollusca (snails, clams, squids)
Annelida (earthworms, leeches,
marine worms)
Arthropoda (insects, spiders, crustaceans, centipedes)
Echinodermata (sea stars, sea
urchins, sand dollars, sea cucumbers)
Notable Characteristics
multicellularity, specialized cells
but no tissues, asymmetry, incomplete digestive system
radial symmetry, true tissues, incomplete digestive system
cephalization, bilateral symmetry,
mesoderm, complete digestive system
pseudocoelom, complete digestive
system
true coelom, organ systems, some
with primitive brain
segmented body, primitive brain
Example
sponges
segmented
body,
jointed
appendages, exoskeleton, brain
complete digestive system, coelom,
spiny internal skeleton
insect (dragonfly)
jellyfish
flatworm
roundworm
snail
earthworm
sea urchin
Protostomes and Deuterostomes
Most invertebrates (and higher animals) can be placed in one of two groups based on how they develop as embryos.
The two groups are called protostomes and deuterostomes. As shown in Figure 1.1, organisms in the two groups
1
www.ck12.org
have different ways of forming the coelom and mouth, among other differences.
Mollusks, annelids, and arthropods are protostomes. Echinoderms and chordates are deuterostomes. This distinction
is important. Why does it matter? It shows that echinoderms are more closely related to chordates than are the other
invertebrate phyla. This is not apparent based on other, more obvious traits.
FIGURE 1.1
Protostomes vs. Deuterostomes. In protostomes such as mollusks, the coelom
forms within the mesoderm. In deuterostomes such as echinoderms, the coelom
forms from a pouch of endoderm. How
does the formation of the mouth differ in
these two groups of animals?
Vocabulary
• Annelida: Invertebrate phylum of segmented worms, such as earthworms.
• Arthropoda: Invertebrate phylum of animals characterized by a segmented body, jointed appendages, exoskeleton, and brain.
• Cnidaria: Invertebrate phylum that includes animals such as jellyfish and corals; characterized by radial
symmetry, tissues, and a stinger called a nematocyst.
• deuterostomes: Animals in which the coelom forms from a pouch of endoderm.
• Echinodermata: Invertebrate phylum of sea-dwelling animals characterized by complete a digestive system,
coelom, spiny internal skeleton.
• Mollusca: Phylum of invertebrates that are generally characterized by a hard outer shell, a mantle, and a
feeding organ called a radula.
• Nematoda: Phylum of invertebrates called roundworms, which have a pseudocoelom and complete digestive
system.
• Platyhelminthes: Invertebrate phylum of flatworms; characterized by a flat body because they lack a coelom
or pseudocoelom.
• Porifera: Invertebrate phylum of sponges; have a non-bony endoskeleton and are sessile as adults.
• protostomes: Animals in which the coelom forms within the mesoderm.
2
www.ck12.org
Concept 1. Invertebrate Classification
Summary
• Eight invertebrate phyla contain most invertebrate species.
• Invertebrates (and higher animals) can also be placed in one of two groups based on how they develop as
embryos.
Practice
Use this resource to answer the questions that follow.
• http://www.hippocampus.org/Biology → Biology for AP* → Search: Protostomes and Deuterostomes
1.
2.
3.
4.
5.
What is the main difference between protostomes and deuterostomes?
What is meant by "mouth first or second"?
Compare the location of the mesoderm in protostomes and deuterostomes.
Which develops first in annelids, the mouth or anus?
Give three examples of annelids.
Review
1. Describe evidence showing that echinoderms are more closely related to chordates than are other invertebrate
phyla.
2. Assume you have discovered a new invertebrate. It has a segmented body, a brain, and jointed appendages. In
which phylum would you place it? Why?
3