Thursday, August 25, 2011

The Lowdown on Legs


One of the best things about choosing invertebrates as my blog topic is that I’ll never run out of subject matter! But that also makes it challenging to pick what to write about now. So, today’s topic is legs.

Legs are one of the main characteristics scientists use to separate invertebrates into various groups. For example, all insects, without exception, have 6 legs. Spiders always have 8. Centipedes (the name means “100 feet”) have one pair of legs per body segment and millipedes (name means “1000 feet”) have two pairs of legs per segment. The number of legs found on crustaceans such as crabs and lobsters tends to vary, but usually they have 10 or 12.

All the invertebrates mentioned above are placed in the Phylum Arthropoda, which means “jointed appendages.” Despite having no internal skeleton, arthropods have movable, jointed legs somewhat similar to our own. Below is a link to a diagram of some insect legs and how they compare to human legs.

http://www.daviddarling.info/images/insect_legs.jpg

Arthropod legs are adapted for many different functions, in the diagram. Many insects’ hearing organs, known as tympanum, are found on the first pair of legs. These organs are sensitive to vibrations and are especially useful to insects that “sing” such as cicadas, crickets, and katydids.

I may post on this topic again as I learn more about insect anatomy in my general entomology class. It’s an area I’m looking forward to understanding better!

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