What did the spider evolve from? Just curious.
Spiders are Arthropods - meaning mostly that they they have an exoskeleton. Chelicerata is the group they are in. Their main cousins are horseshoe crabs, scorpions, trilobites.
All of the Arthropoda evolved from early Cambrian species. Chelicerates have their body parts (head, thorax, abdomen all fused), other arthropods don't. Trilobites dominated the the late Cambrian seas, along with sea scorpions.
Sea spiders (pycnogonids) are very primitive (meaning unchanged from a beginning ancestor ~500 million YA) and are probably descended directly from the ancestors of all modern terrestrial spiders.
I'm going to stick my neck out here (spider bite!) and offer a couple promising-looking sites I came across from a quick Google search. I haven't read it thoroughly, and I'm no spider expert, so I don't know how reliable they are...
Thanks all! For the record, I'm phobic and I like to know my enemy...
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