Sleuthing Spiders in the San Juans – Day 3 – Classifying Spiders, the Very Beginner Basics!


Spider Sleuthing Day 3 – Classifying Spiders. The (VERY) Beginner Basics. Spider classification (for North America) consists basically of two different groups. These are the infraorders: Araneomorphae (the “true” spiders) and Mygalomorphae (the tarantulas and trapdoor spiders).

What are “true” spiders? Why those are the ones that aren’t Mygalomorphs! What??? I confess, I’m having to read up on this as I type this post. I DID, however, disclose that I am an entomologist and not an arachnologist in my DAY 2 post, and I can count to 6 (if you read my earlier post, you’ll get my joke), and that is high enough to tell you that these groups are partially differentiated by the number of book lungs a spider has.

Book lungs are the main respiratory organ in arachnids. Mygalomorphs have 4 book lungs and Araneomorphs have only 2. See, we got to SIX! 😁

The other difference between these two spider groups has to do with how they chew. Well, sort of. A more scientific description would be to say the directionality of movement of their chelicerae.

Yep. Let’s just make it easy today and say, Mygalomorph’s mouthparts move in a parallel direction (move your first two fingers towards each other like you’re making air quotes) and Araneomorph’s mouthparts are oriented in an opposing way (touch your forefinger to your thumb in a pincer-like way). For more about this, you’re welcome to delve into the deep world of spider systematics here – https://www.jstor.org/stable/2097274?seq=1#metadata_info_tab_contents

Sorting spiders involves numerous other factors including morphological differences such as eye arrangement, hairs, body shape, number of claws and even what type of web they make or whether they make a web at all!

As to webs, well that’s going to be a post of its own. There are ALL sorts of webs and knowing their names and being able to identify them will be a tool for figuring out what sort of spider you may have.

I have run out of time for my post today, but I will leave you with a few links to check out so you can learn more of the basic morphology that all spiders share: 8 legs, head or (cephalothorax region), abdomen…Oh, and the cutie on my finger is one of my house spider friends. She’s a jumping spider (Salticus scenicus) and her name is Skipper.

(Salticus scenicus)

More on Spider Anatomy here – https://www.earthlife.net/chelicerata/s-anatomy.htmlhttp://biologyandbiodiversityinspiders.weebly.com/spider-anatomy.html

***Hint to remembering the Mygalomorphs – *The majority of species in the Mygalomorphae are tarantulas, in the family Theraphosidae (in French, a tarantula is called a ‘mygale’

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