Imagine a little box of spoons. Now, imagine on moving day that that box of spoons is put into a bigger box with all of the silverware. Now, imagine that that box of silverware is placed into an even bigger box with all of the kitchen stuff.

Now, imagine that the box of kitchen stuff is placed in the moving truck with all of the stuff from your house. In the end the within the truck is all of the stuff from your house, within kitchen box are all of the things from the kitchen, and within the spoon box are just the spoons.

In the same way, we will group organisms according to their physical appearance into hierarchical categories.

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In this unit we’re going to discuss invertebrates by naming what characteristics they have, and placing them in categories accordingly. For example, jellyfish are placed in the Cnidarian category due to their radial symmetry and stinging cells.

Meanwhile Cnidarians are placed in the invertebrate category due to their lack of a backbone. Furthermore, invertebrates are placed in the animal category because they are multicellular, eukaryotic (having cells containing true nuclei), and heterotrophic (required to eat molecules to survive: do not produce their own food).

In this way, we classify animals; we place them in categories according to physical characteristics (modern biology classifies organisms according to DNA similarity) they have (radial symmetry, stinging cells, and lack of backbone, for example).

As you can see, the largest box or category, “animals”, is much larger than the tiny category “jellyfish”. The number of organisms in each category gets progressively fewer as you classify things from animals in general, to jellyfish in particular. The categories follow this structure:

• Kingdom: The domain in which living organisms are classified.
• Phylum: The subdivision in which all classes below have the same body plan.
• Class: Organisms that share one or more attributes.
• Order: Containing one or more families.
• Family: Organisms descended from the same ancestors sharing relatively similar characteristics.
• Genus: Groups of species that are structurally similar or phylogenetically related.
• Species: Organisms capable of mating with one another.

An easy way to remember the order of the hierarchy is to think of this mnemonic: Kings Play Cards On Funny Green Stools—each first letter stands for the first letter of a level in the hierarchy (Kingdom, phylum, etc).

For example the classification of the jellyfish the Portuguese Man-O-War (shown):

• Kingdom: Animalia (Multicellular, heterotrophic, eukaryotic)
• Phylum: Cnidaria (Radial symmetry, stinging cells)
• Class: Hydrozoa (very small predatory animals, mostly saltwater, solitary and colonial)
• Order: Siphonophora (Colonies of specialized cells which could not survive on their own and resemble one organism)
• Family: Physaliidae (Organisms of the genus Physalia)
• Genus: Physalia (Colonies of specialized cells which float on the Indian or Pacific Oceans via gas-filled bladders)
• Species: P. physalis(Portuguese Man-O-War)

And that’s it! To get a better handle on this (it’s confusing at first!), here’s a simple activity you can do that’s fun and easy. Here’s what you need:

• Card stock
• Printer
• Ziploc bags

Here’s what you do:

1. Print out the Challenge: Classifying Invertebrates file. You’ll want to print several copies the cards on card stock. You should have enough so that each team (or each student) gets a complete set of cards. They can be stored in zipper-type bags for future use.
2. Work in teams to correctly classify the invertebrates. You can compare your answers to the key shown below.
3. For more of a challenge, time yourselves to see which team (or student) can complete the classification fastest. One player shuffles the cards and places them in a pile, then serves at the times for the other team.
4. When you’re ready for answers, print out the Answer Key.

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I have to admit, one of my all-time favorite animals is the octopus. It’s not only an invertebrate, but amazingly intelligent and can be poisonous (like the blue-ring Octopus shown here) or not.

The octopus is an animal because it’s multi-cellular (more than one cell, so amoeba and protists are not animals), it’s moveable (not like a fungus), and a heterotroph (not a plant). Their life cycle starts with a single cell that divides and leads into a multi-celled adult.

All molluscs have a muscular foot on the bottom, and there are three basic shapes: gastropods (snails and slugs), bivalves (oysters and clams), and cephalopods (octpous and squid).

The Indonesian Mimic Octopus, Thaumoctopus mimicus. This fascinating creature was discovered in 1998 off the coast of Sulawesi in Indonesia, the mimic octopus is the first known species to take on the characteristics of multiple species. This octopus is able to copy the physical likeness and movement of more than fifteen different species, including sea snakes, lionfish, flatfish, brittle stars, giant crabs, sea shells, stingrays, jellyfish, sea anemones, and mantis shrimp.

This animal is so intelligent that it is able to discern which dangerous sea creature to impersonate that will present the greatest threat to its current possible predator. For example, scientists observed that when the octopus was attacked by territorial damselfishes, it mimicked the banded sea snake, a known predator of damselfishes.

Invertebrates are organisms without backbones. Let’s look at two very simple types of invertebrates; Sponges and Cnidarians. Sponges (Phylum Porifera), found in oceans all over the world, are made up of colonies of specialized cells—some help push water through the sponge, some help it feed, some are responsible for reproduction, etc.

They feed by filtering water through its pores. They have flagella on the inside that drive the water through and pick up particulates in the water. In this sense, they are known as sessile filter feeders. Sponges are attached to the ground below them—they are sessile (unable to move). However, sponges can move around at certain times in their lifespan.

Scientists use to think they were plants, but we know now that they are in fact animals. Besides their specialized cells, sponges do not have any organs, nerves, or even true tissues. They are held together through the cooperation of the colony.

Cnidarians (don’t pronounce the ‘c’, so it sounds more like “nay-DAR-ee-ons”) also are radially symmetrical. This means they have a circular body plan such that any way you cut them in half the sides will be equal. There are two basic body forms; polyp and medusa. The polyp is a cup-shaped body—with the mouth facing upward (sea anemones, for example). The medusa is bell-shaped and has a downward-facing mouth (jellyfish, for example). Some can even start in the medusa stage and then move into the hydra stage.

Painful stinging cells, called nematocysts, make the phylum Cnidaria especially notable. Jellyfish and sea anemones are just two examples of these painful creatures. The nematocysts are, in fact, long hollow threads that are used to trap prey. Additionally, these nematocysts are triggered externally, so even if you come across a dead jellyfish don’t step on it!

A Cnidarian with a polyp body plan, a sea anemone, and a Cnidarian with a medusa body plan, a jellyfish. Notice the upward facing mouth of the polyp, and the downward facing one of the jellyfish.

Cnidarians, unlike sponges, have true tissues. They digest their food in a gastrovascular cavity—a large cavity containing digestive enzymes. The digestive cavity also has circulatory functions. Cnidarians, like sponges, can form colonies. Colonies of polyps form the jellyfish the Portuguese Man-O-War. Similarly, colonies of cnidarians form on calcium carbonate skeletons to make coral reefs.

Echinoderms, meaning “spiny skin”, are radial symmetric marine animals. They are found at all depths—both shallow and deep water. They play important roles in their ecosystems. Despite appearances, they do not have skeletons. The “spiny skin” is, in fact, skin covering a spiny endoskeleton (internal skeleton).
How do echinoderms move? How do they feed themselves?

Echinoderms have a water vascular system responsible for gas exchange, movement, and feeding. This system is an internal network of fluid-filled canals. Depending on the species, they have various ways of getting food into their water vascular systems. Some are filter feeders, while others (such as starfish) are predatory. They use this system in place of gills, heart, and a closed circulatory system. Although they do not have brains, they do have nerve nets responsible for receiving and processing sensory information.
What about their reproduction? They reproduce sexually—with sperms and eggs. Some species provide brainless parental care.

Here’s a super-short quick snippet about starfish:

Echinoderms are found worldwide, and play important roles in their environments. Primarily, they are strong links in the food chain. For example, they control the growth of algae on coral reefs (making it easier for the reefs to filter-feed), and they serve as food for other organisms (otters, for example).

Starfish Dissection

You can do this dissection at home! Here’s a very inexpensive starfish dissection guide and starfish specimen and simple dissection to

ols!

Arthropods, organisms in the phylum arthropoda, are organisms with segmented bodies and appendages on at least one segment. They use these appendages for defense, feeding, sensory perception, and locomotion. We usually see them everyday: fly on the wall, or perhaps moth by the light. The phylum is incredibly divers and the organisms within it have developed numerous adaptations to deal with environments from your kitchen counter to the Amazon!

Arthropoda is the largest phylum in the animal kingdom. Examples of Arthropods include: scorpions, crabs centipedes, insects, and crayfish.

Arthropods are covered my hard external skeletons. When they grow they shed these skeletons in a process called molting. For gas exchange aquatic arthropods have gills, while terrestrial (land-based) arthropods have either a tracheal systems or book lungs. Tracheal systems are air sacs fed by pores in the exoskeleton. Book lungs are gills modified to extract oxygen from air.

Six classes of crustaceans are recognized in the word, and almost fifty two thousand species. Most of them are aquatic. Interestingly, they have a brain in the form of ganglia (connections between nerve cells).

In the phylum Mirapoda (Centipedes and Millipedes), over thirteen thousand species exist! All of them live on land. Some species have fewer than ten legs, while some can have over seven hundred and fifty!

Spiders (a type of Arachnid) are found in the class Araneae and the subphylum Chelicerata. This subphylum includes scorpions, mites, and ticks as well as spiders. Arachnids characteristically have four pairs of legs, a pair of chelicerae (see table at the end of this section), and a body organized into the cephalothorax (a fusion of the head, thorax, and abdomen). There are eleven subgroups of Arachnids.

Insects are not only the most diverse subgroup of arthropods, but with over a million discovered species it is the most diverse group of animals on earth. Although they can’t all be as beautiful as a butterfly, they all play important roles in their ecosystems—just think of where we would be without bees!

The segmented exoskeletons of insects have a hard, inner layer called the cuticle, and a water-resistant outside layer called the exocuticle. Insects are divided into two major groups: winged insects and wingless insects. Air is taken in through structures called spirials, and delivered directly to the body.

Sea angels used to be known as a pteropod (small swimming sea slugs), but now are recognized as pelagic marine opisthobranch gastropod molluscs. Sea angels, also called cliones, live all over the world, both in polar and equatorial seas. Sea butterflies are similar to sea angels, but they also have a shell. Some sea angels even eat sea butterflies, which are slower and larger than themselves!

Sea angels are transparent, gelatinous, and unusually small (the average size is only an inch). Since sea angels are simultaneous hermaphrodites, their fertilization occurs internally and eggs are released to float with the ocean currents until they hatch on their own.

Although sea angels usually enjoy slow movement, as they only beat their winds once a second, they can also put on a burst of speed if they’re catching dinner.

If you have ever gone searching though tide-pools at the beach, you’ve probably seen your fair share of Mollusks. This is because mollusks live mainly in the sea (in the intertidal zone), although some live in freshwater.

Mussels, scallops snails, oysters (from which we get pearls!), and clams are only a few examples of types of mollusks. The mollusk body plan generally involves a muscular foot for locomotion, a body housing organs, a head with eyes or tentacles, and a mantle (which creates the shell). Usually, they absorb oxygen from the water using gills.

Only mollusks have a structure called a radula. Radulae (the plural of radula) are composed mostly of chitin, and can be as simple as a structure used to scrape algae off rocks, to the beaks of octopuses.

Quadrants are an archeologist’s best friend. Basically, they’re large, wooden frames scientists—especially archeologists—use to keep track of exactly where they find things during a dig.

A “dig” is what archeologists call the process of uncovering artifacts. You can also use this tool in the backyard when investigating a field of bugs, insects, and other invertebrates!

The quadrant is divided into smaller sections by pieces of string tied at regular intervals. Where the string intersects, it creates square sections that can be easily labeled and referred to in a research notebook.

This way, when the scientists return to their labs they can remember exactly where they found everything—a very important part of the science of archeology!

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Here’s how archaeologists make before their next dig (I’ll show you how to make a quicker version in a minute):

• 20 feet of cheap, ¾ inch PVC piping (there’s no need to get the good stuff—the cheapest you can find will work).
• PVC elbows
• PVC glue (work in a well ventilated area).
• A saw.
• String.
• Drill with a small bit.
• Tape measure.

Let’s make it!

1. Cut the pipe into four 39 inch pieces.
2. On a flat surface, create a square with the PVC using the elbows and the glue. Make sure that the square is in one plane.
3.  Drill holes in the pipes at the midpoint, and at ½ and ¾. Drill all the way through. Connect the opposing holes with string. You should end up with 16 equal sections.

And now… they excavate!

Now, this is usually overkill for most kid archaeologists. To make a simpler version, substitute sticks or yardsticks for the PVC pipe, and secure the string grid around the rulers. If you really want, you can simply lay the string on the ground and skip the frame altogether.

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Some animals glow under ultraviolet light.  Jellyfish are a prime example of these glowing animals.  Under normal conditions, worms do not glow.

However, scientists have been able to genetically alter some worms so that they will glow under an ultraviolet light.  To do this, scientists engage in genetic engineering.  They inject the gene that makes jellyfish glow into the worm.

Even though jellyfish and worms are very different animals, their genes, like the genes of most living things, are actually quite similar.  So, the worms with the injected gene will glow just like jellyfish do.

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A glowing worm is kind of cool, but what is the actual scientific benefit to this?  It turns out that glowing worms can actually tell scientists quite a lot about what’s going on inside the worm.  Observers can actually see the nervous system in action, so they can observe how nerve cells communicate with each other.  This is far more powerful than a dissection, because the observer is able to see how things work while the worm is alive.  The function, rather than just the structure, of the animal can be observed.  This technique, of adding a gene to make an organism glow and then looking at how a certain body system works, has been used with other organisms besides worms.

It is important to point out that these glowing worms are not the same as the animal commonly called a glowworm.  Glowworms are actually not worms at all (although they do look somewhat like worms.)  They are actually insects in the larval stage which have the property of bioluminescence, which is defined as the ability to emit, or give off light.  In glowworms, the bioluminescence is generally the result of a chemical reaction between the waste product of the larva and oxygen.  When the insect undergoes metamorphosis and reaches the adult stage, it will no longer exhibit bioluminescence.

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