Arthropods


Reminder: Clicking on the picture will take you to the site where I originally found it.

Pop quiz -

The word Arthropod means what?
Click to find out
rubber fingers
crunchy skin
jointed legs
Latin name
wiley coyote
Get rid of the monkey please.


Here's a hint. Arthro comes from the same root as the term arthritis. When a person has arthritis, they have swollen, inflamed _________. And pod is familiar in words like Podiatrist - a doctor of the __________ or a PEDestrian ( a person who uses their __________ to get around).

Well, I hope you figured out what an arthropod is. They live up to their name meaning as well. You'll notice that arthropods have a lot of pods for getting around.

All of this fantastic ability is the result of a hard exoskeleton. This tough shell is what makes arthropods rulers of sea, land and air.

All arthropods have segmented bodies. Bodies may be in two, three or numerous segments. The bodies of arthropods are also equipt with jointed appendages. (I figure that if you've read this far, you already figured out the quiz.) Arthropods also have jointed mouthparts. This allows amazing chewing adaptations. Arthropods also have a more sophisticated nervous system than many invertebrates.

The time has come to meet some of the arthropods.




Crustaceans

Crustaceans are mostly marine arthropods. Most familiar in this class are crabs, lobsters and shrimp. Crustaceans are important to humans commercially, but they're also important in other ways.

Some crustaceans are scavengers. They will feed off detritus (dead stuff) on the bottom of lakes, oceans and ponds. Most are also predators on fish and other life. Some crustaceans, the daphnia, are microscopically small, while there are some crabs which are very large. Make sure you take a good look at the crustaceans.

Crustaceans include the typical invertebrates on a sea-food platter, such as lobster, crab and shrimp. There are also brine shrimp, natives of the Great Salt Lake. Crayfish are crustaceans too, and they're a lot like little lobsters. Forgive me if I sometimes pronounce them as "crawfish," as I spent a little time in the South. All these are decapods, or ten-legged crustaceans.

Not all crustaceans are considered delicacies. The barnacles (who are not decapods) are crustaceans who make a habit of attaching their shell to any solid object. Often, it's the bottom of a boat, which causes problems for the sailing types. Barnacles are filter feeders and strain the water for their food.

There is one very important land crustacean you may have seen. These are known as isopods. You may have seen them called sow bugs, pill bugs, roly-polys, roll-up bugs or another name. While they resemble insects in size and location, they're not insects. They are crustaceans. They live un moist earth and can be found under rocks, under decaying leaves and sometimes they eat away at the roots of plants.

One crustacean you're not likely to see is the daphnia, or water flea. At least you won't see them without the help of a microscope. These little crustaceans are as small as some protists, yet they are true crustaceans.

Diplopods and Chilopods

Centipedes and millipedes may seem a lot alike, but they're easy to tell apart if you know what you're looking for.

Centipedes are known as chilopods. They have a whole lot of segments, but only one pair of legs per segment. They are poisonous, but have a weak bite. If they happen to pierce the skin, the bite is similar to that of a bee sting. Often, a centipede's legs are spread out to the side of the body, making them easy to see. The centipede's body is usually flat. Chilopods are carnivores.

Millipedes, on the other hand, are known as diplopods. They have two or more pairs of legs per segment. Those in the U.S. are not poisonous. The legs of a millipede are under the body, and the body is usually round. Diplopods are usually herbivores.

Now that you know how to tell them apart, it's easy to see why they're in two different classes. Although they resemble each other a little, they have very different lives. Both the centipede and millipede are terrestrial, meaning they live life on land. Both prefer to be in moist places, and you'll often encounter them under rocks and in the soil. Millipedes aren't dangerous, but they can be a garden pest. Some people even keep millipedes as pets. The giant millipede (pictured) is from Africa. It's illegal to buy and sell them in the States, but their smaller cousins may be nearby.

Arachnids

No other group of invertebrates are as likely to bring fear as the arachnids. Spiders and scorpions aren't exactly cuddly, and who really wants a mite or a tick to be a constant companion? Arachnids are an interesting class though.

The most common of arachnids are the spiders. They are characterized by their eight legs, two-part bodies and their fangs. Most, but not all spiders spin webs.

There are many different types of spiders. They range from the extremely helpful to the deadly. The United States of America only has three major poisonous spiders. They are the black widow, the brown recluse and the hobo, or aggressive house spider.

Believe it or not, scorpions are closely related to spiders. They have very similar mouths and legs. One noticeable difference is the tail of the scorpion. Actually, it isn't a tail, but an elongated body. At the tip is a venom gland. This is also known as the stinger.

Scorpions aren't as deadly as you may have been led to believe. Some are harmless to humans. For the poisonous ones, death is extremely rare among healthy adults.

Scorpions don't make the greatest pets, but they aren't bad to have in the environment. They are carnivorous and get rid of some pesky insects. There is a lot to learn about the scorpions.

While I have a slight fondness for the maligned spiders and scorpions, I still have a hard time with ticks and mites. The bloodsucking critters are generally parasites and evil. OK, I know that most mites are actually beneficial, but they still freak me out.

There are other arachnids which are fun. Harvestmen, also called daddy long-legs, are arachnids, but not spiders. They are considered beneficial and prefer to scavange rather than attack prey.

All that we have yet to discuss are the whip scorpions and pseudoscorpions. Both of these are harmless and you aren't likely to run across them anytime soon.

Insects

You know these creatures. There are over 100 million species, so chances are you've run into one or two insects before.

Let's start with the basics. All insects have a three-part body as an adult. There is the head which contains a primitive brain and some sensory organs, such as antennae or eyes. Next comes the thorax where the three pair of legs are found, and most often wings. Finally, there is the abdomen where the reproductive organs and other vital organs are housed.

Insects re extremely diverse and advanced (for spineless animals.) The insect class is divided into many orders of insects. Not all will be listed here, but many are familiar to you.

Among the insects, there is remarkable organization. Social structures of ants and bees amaze scientists. Insects are the first species which demonstrate division of labor. There is also communication among the insects, as demonstrated by bees. There are some solitary insects, but many have found ways to work together.

Ants are amazing because they have learned how to raise their own crops, defend territories and even raise herds of aphids. Such a degree of advanced societal life is rare and facinating.

I have no way to tell you about all of the types of insects here. If there is a nasty, nice or neutral insect which interests you, please find out more!

Horseshoe crabs and trilobites

You could say that horseshoe crabs are in a class by themselves. These poor mis-named critters are neither crabs nor horseshoes, but belong to a class called Meristomata. They are more closely related to spiders and scorpions than they are to the crabs.

In spite of looking like a well-armored tank, these creatures are quite harmless. I've picked one up before. You have to be careful of the tail (called a telson) because it can flip and hit you, but the horseshoe crab uses it to turn over if it winds up on its back.

Horseshoe crabs are useful in medical research. Their blood has some unusual properties. Scientists have figured out how to extract blood from horseshoe crabs without killing them. This has lef to many advancements sin joint-replacement and cancer studies.

The other arthropod I want to mention is unusual. It's not rare or weird, but it has been extinct for millions of years. This animal is the trilobite.

These little critters appeared as part of the cambrian explosion. They show up in the fossil record about 520 million years ago. They were amazing survivors and inhabited the seas for almost 300 million years. That's quite a feat!

Not a lot is known about the trilobites. No body has seen a live one. We know from fossils that they crawled upon the shallow ocean floor. They probably are dead or decaying organic material, but that isn't certain. We do know they left a lot of fossils about, and that they managed to survive from the dawn of animal life until the extinction which occurred right before the dinosaurs.

All the way back to the animal page,
see sponges,
near the cnidarians,
meet the mollusks,
enquire about the echinoderms,
wade through the worms,
commune with the chordates or
over to the overview.