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Introduction to Invertebrates

Of all the living organisms on Earth, humans are perhaps most familiar with animals. City dwellers might find birds or squirrels in a park or keep domesticated dogs, cats, and goldfish as home pets. Humans living in rural areas might raise pigs or chickens, or encounter coyotes or snakes. These familiar animals are generally vertebrates, or animal species with backbones. However, only three percent of all animal species are vertebrates. The vast majority of animal species do not have backbones. These animals are called invertebrates.


<p><strong>Fig. 3.1.</strong> A free-living marine flatworm (<em>Pseudobiceros</em> sp.) on a gold-mouth sea squirt (<em>Polycarpa aurata</em>), East Timor</p><br />

Invertebrates occur in many different sizes and shapes (Fig. 3.1). Some invertebrate species, such as nematode roundworms, are microscopic organisms that are only a few millimeters long. Other invertebrates are very large, such as the lion’s mane jellyfish, whose tentacles stretch up to 75 meters. Some invertebrate species, such as crabs or snails, are easily recognizable as animals, with a distinct head, eyes, and mouth. Others have a very different body plan, often without obvious heads. Sea stars, sponges, and corals are good examples of these. Some invertebrates, including fast-swimming squid or flying insects such as bees, dragonflies, and moths, can move very quickly. Others species, such as corals, fan worms, sea anemones, and sponges, remain stationary for much, if not all, of their lives.


Invertebrates are important to humans in many respects. Species of marine invertebrates that are valuable as seafood include squids, clams, oysters, shrimp, and crabs. On land, insects can both consume and protect crops and can pollinate flowers. Some insects, such as mosquitoes and fleas, are known to spread human diseases.


Since invertebrates comprise the vast majority of animal species on Earth, it is important to develop an understanding of their biology and an appreciation for their biodiversity.


Ocean Literacy Principles

Principle 5: The ocean supports a great diversity of life and ecosystems.

Ocean Literacy Fundamental Concept: Ocean life ranges in size from the smallest virus to the largest animal that has lived on Earth, the blue whale (OLP 5a).


To build an understanding of ocean life and diversity, it is important to appreciate that much of that ocean diversity is made up of invertebrate animals.


These concepts will be explored in this unit through the following activities and investigations:


Activity: Invertebrate Phylum Project

Become an invertebrate expert and teach your classmates about your specialization.


Activity: Nematocysts

View unfired and fired nematocysts under a microscope.


Activity: Corals

Examine coral specimens in detail and record their features.

Question Set

Question Set: Worms


Activity: Gastropod Shell Description

Describe differences among gastropod shells.


Activity: Squid Dissection

Examine the internal and external features of a squid.


Activity: Aquatic Invertebrate Behavior

Investigate the behavior of various aquatic invertebrate taxa through careful experimentation and observation.


Activity: Comparing Echinoderms

Use investigative skills to compare different groups within the phylum Echinodermata.


Activity: Tunicate Life History

Compare the structure and function of larval and adult tunicates.

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Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.