Chelicerata: Welcome To The Delightful World Of The Chelicirates

The Chelicerata, which I have called a subphylum here for convenience (but which is just as well called a phylum in some texts) is an extremely ancient group of arthropods, including the extinct Eurypterida.

The first ancestral chelicerates probably evolved about 600 million years ago. They are now distinguished from the other arthropod groups by the possession of (at least) six pairs of appendages.


Chelicerate Spider Araneus Trifolium

These normally include four pairs of walking legs, a pair of chelicerae and a pair of pedipalps. They have no mandibles, no antennae and the body is divided into two (not three) sections, as in the Uniramia. They are however normally bilaterally symmetrical, have a through gut, have uniramous appendages, a non-calcareous exoskeleton and are gonochoristic.

No chelicerates possess jaws for biting and chewing, but suck up their food in liquid or semi-liquid form. However, this food may have been seriously torn up by the chelicerae before ingestion. Most species go in for external digestion to some extent.

Meaning they secrete digestive juices onto the food item, as it is held close to the mouth; or inject digestive juices into the prey’s body – and suck up the half digested soup that results.

Chelicerata Centruroides sculpturatus
Juvenile Arizona bark scorpion (Centruroides sculpturatus) eating a Chironomid midge.

The inclusion of the class Pycnogonida in the Chelicerata is generally accepted, but not scientifically proven. The fossil record for pycnogonids is very scant and they differ in many ways from the other chelicerates.

The Chelicerata contain more about 80,000 species known to science, most of which are Arachnids divided almost evenly between the spiders and the mites.

Use the links below to explore the Chelicerata section of our site!

Chelicerate Spider On Plant

Phylum Arthropoda; Subphylum Chelicerata:

Gordon Ramel

Gordon is an ecologist with two degrees from Exeter University. He's also a teacher, a poet and the owner of 1,152 books. Oh - and he wrote this website.

One Comment

  1. Dear Gordon, I’ve met you via ENTOMO-L discussion group a long time ago. I used to spend to much time reading/sorting interesting messages. I asked for help from time to time that period. Some guys helped. Maybe you remember me – a museum curator from a small city museum in city of Split, Croatia. We didn’t have web site that time and the internet connection was with dial up… Than I lost contact to the group but I kept few great contacts from that times and I also remember you from that times. Such a great leaning tool! That times you were in Bulgary I think, or Greece.
    I still take care of our old beetle collection and teach a lot of school kids, or younger kids, sometimes even students. Workshops etc. Here it was me here when my hair wasn’t grey yet like now at my workshop “Insects”. I take care of an old beetle collection and teach a lot schoolkids, or younger kids, sometimes even stoudents. We have a site but still not bilingual. Maybe you can try to google it if you want to search it. Cheers!

    Best of luck!


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