Exploring Our Fluid Earth

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.

Fig. 3.1. A free-living marine flatworm (Pseudobiceros sp.) on a gold-mouth sea squirt (Polycarpa aurata), East Timor

Image courtesy of Nick Hobgood, Wikimedia Commons

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: