Invertebrates - Advanced Douglas Wilkin, Ph.D. Jennifer Blanchette Say Thanks to the Authors Click http://www.ck12.org/saythanks (No sign in required) AUTHORS Douglas Wilkin, Ph.D. To access a customizable version of this book, as well as other Jennifer Blanchette interactive content, visit www.ck12.org EDITOR Douglas Wilkin, Ph.D. 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-source, collaborative, and web-based compilation model, CK-12 pioneers and promotes the creation and distribution of high-quality, adaptive online textbooks that can be mixed, modified and printed (i.e., the FlexBook® textbooks). 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Printed: January 24, 2016 www.ck12.org Chapter 1. Invertebrates - Advanced CHAPTER 1 Invertebrates - Advanced CHAPTER OUTLINE 1.1 Invertebrates - Advanced 1.2 Invertebrate Classification - Advanced 1.3 Invertebrate Evolution - Advanced 1.4 Sponges - Advanced 1.5 Sponge Structure and Function - Advanced 1.6 Sponge Reproduction - Advanced 1.7 Sponge Ecology - Advanced 1.8 Cnidarians - Advanced 1.9 Cnidarian Structure and Function - Advanced 1.10 Cnidarian Reproduction - Advanced 1.11 Cnidarian Ecology - Advanced 1.12 Flatworms - Advanced 1.13 Flatworm Classification - Advanced 1.14 Flatworm Diseases - Advanced 1.15 Roundworms - Advanced 1.16 Roundworm Classification - Advanced 1.17 Roundworm Diseases - Advanced 1.18 Mollusks - Advanced 1.19 Mollusk Classification - Advanced 1.20 Mollusk Structure and Function - Advanced 1.21 Mollusk Nervous System and Reproduction - Advanced 1.22 Mollusk Body Plans - Advanced 1.23 Mollusk Ecology - Advanced 1.24 Annelids - Advanced 1.25 Annelid Classification - Advanced 1.26 Annelid Structure and Function - Advanced 1.27 Annelid Reproduction - Advanced 1.28 Annelid Ecology - Advanced 1.29 Arthropods - Advanced 1.30 Arthropod Structure and Function - Advanced 1.31 Arthropod Growth and Development - Advanced 1.32 Arthropod Evolution - Advanced 1.33 Arthropod Classification - Advanced 1 www.ck12.org 1.34 Crustaceans - Advanced 1.35 Arachnids - Advanced 1.36 Insects - Advanced 1.37 Insect Structure and Function - Advanced 1.38 Insect Flight - Advanced 1.39 Insect Reproduction and Development - Advanced 1.40 Insect Behavior - Advanced 1.41 Humans and Insects - Advanced 1.42 Echinoderms - Advanced 1.43 Echinoderm Structure and Function - Advanced 1.44 Echinoderm Classification - Advanced 1.45 Echinoderm Ecology - Advanced 1.46 Nonvertebrate Chordates - Advanced 1.47 Tunicates - Advanced 1.48 Lancelets - Advanced 1.49 Nonvertebrate Chordate Evolution - Advanced 1.50 References Introduction 2 www.ck12.org Chapter 1. Invertebrates - Advanced How’d you like this staring at you? This may look like a scary creature from your worst nightmare, but it wouldn’t hurt a fly. In fact, it is a fly! The picture shows the charming portrait of a horsefly, up close and personal. Those big, striped, colorful orbs are its eyes. Did you ever look through a kaleidoscope? If so, then you have an idea of what the world looks like to a horsefly. What other organs do insects like this horsefly have? Besides sensing their environment, what other functions do their organs serve? In this chapter, you will find out. You will read not only about fly eyes. You’ll also read about octopus ink, spider fangs, and other fascinating features of invertebrates. 3 1.1. Invertebrates - Advanced www.ck12.org 1.1 Invertebrates - Advanced • Describe the defining characteristics of invertebrates. What adaptations occurred during invertebrate evolution? The vast majority of animals on earth today are invertebrates. They make up 97% of all animal species and all but one of the animal phyla. The invertebrate phyla include a wide array of body plans and adaptive strategies. The evolutionary changes that took place among the animals within the invertebrate phyla were extremely important steps in the development of more complex organisms. Characteristics of Invertebrates Invertebrates are defined as animals that do not have a spinal, or vertebral, column. Invertebrates also lack a cartilagi- nous or bony internal skeleton. Some invertebrates have either exoskeletons or internal skeletons ( endoskeletons), but they are not made of bone or cartilage. Generally, invertebrate skeletons are made of calcium carbonate or, in some cases, organic molecules such as complex carbohydrates. As members of the animal kingdom, all invertebrates are made up of eukaryotic, heterotrophic cells that do not have a cell wall. Beyond that feature, the physical characteristics of invertebrates vary widely. They include such diverse species as jellyfish and tarantulas, both of which are shown in the Figure 1.1. Digestion Invertebrates have two general types of digestive systems. They either have a digestive cavity with one opening or a digestive tract with two openings. In the first case, the opening serves as both the mouth and the anus. This is the case with the earliest invertebrate phyla, such as Porifera (which contains sponges) and Cnidaria (which contains corals and jellyfish). These two phyla will be discussed in more detail in additional concepts. A digestive tract with two openings uses one opening for the mouth and the other for the anus, allowing food to be processed in stages as it progresses along the tract. Many invertebrate phyla have a digestive tract with two openings. 4 www.ck12.org Chapter 1. Invertebrates - Advanced FIGURE 1.1 A jellyfish, also known as a sea jelly (left), and a tarantula (right) are members of the phyla Cnidaria and Arthropoda respec- tively. These organisms demonstrate the large diversity of invertebrate species. Movement All invertebrates are capable of movement during at least one of their stages in life. There is a great deal of variation in the types and complexity of these movements. For some invertebrates, movement consists of a rhythmic pulse that propels the animal along water currents in the ocean. These animals, such as jellyfish, are not able to move with any real sense of direction. Invertebrates with a worm-like body plan, such as roundworms, can usually move in a directed manner, either forward or backward. This movement does not depend on water currents. Some invertebrates have appendages that allow them to exhibit very precise movement in all directions, including the ability to navigate an uneven surface. Nervous System Most invertebrates have a nervous system that allows them to detect aspects of their environment and elicit responses to external stimuli. In some cases, this consists of a simple nerve net throughout the body wall of the animal that can detect touch. The Figure below shows a diagram of coral, illustrating the nerve net lining the body wall. However, many invertebrates have primitive brains that are capable of much more sensitive perception. There are even some invertebrates, such as octopi and squids, that have both complex eyes capable of forming images and a well-developed brain. FIGURE 1.2 The nervous system in invertebrates. Reproduction Although invertebrates are all capable of sexual reproduction, most phyla include species that are also capable of asexual reproduction. Unlike sexual reproduction, asexual reproduction does not involve the formation or fusion of gametes. One type of asexual reproduction is called fission. In this process, the animal simply divides itself into two parts. Each part then regenerates the missing region to form a whole organism. Another method of asexual reproduction is called budding. In budding, the parent usually forms a small protrusion that remains attached to the parent while developing into a new individual. In some colonial invertebrates, the new individuals may remain attached to the parent throughout their lifetime, forming large interconnected colonies. 5 1.1. Invertebrates - Advanced www.ck12.org Vocabulary • asexual reproduction: Reproduction involving only one parent; it occurs without a fusion of gametes and produces offspring that are all genetically identical to the parent. • budding: A form of asexual reproduction in which a new organism develops from an outgrowth, or bud, on another one; the bud may stay attached or break free from the parent. • endoskeleton: An internal skeleton that provides support and protection. • exoskeleton: A non-bony skeleton that forms on the outside of the body of some invertebrates and provides protection and support. • fission: Asexual reproduction in which a parent separates into two or more individuals of about equal size. • invertebrate: An animal that lacks a vertebral column, or backbone. • nerve net: The primitive nervous system of cnidarians; it is non-centralized and consists of interconnected neurons spanning the body wall. • sexual reproduction: Reproduction involving the joining of haploid gametes, producing genetically diverse individuals. Summary • Invertebrates are animals that do not have a spinal column, or backbone. In addition, invertebrates lack an internal cartilaginous or bony skeleton. • As members of the animal kingdom, all invertebrates are made up of eukaryotic, heterotrophic cells that do not have a cell wall. • All invertebrates have digestive systems and most have nervous systems as well.