How many different types of arachnids are there?

I have read books that have said 11, 12, 15, and 17. Now given that information, every time a book lists more than 11, it neglects to mention any past the 11nth one. So here are those 11 and please correct me or add to this list if you know more, and where you got your info would help me a great deal as well.

1. Spiders- Aranae
2. Mites and Ticks- Acari
3. Scorpions- Scorpiones
4. Pseudoscorpions- Pseudoscorpiones
5. Sun spiders- Solifugae
6. Whip scorpions- Uropygi
7. Microwhip scorpions- Palpigradi
8. Schizomids- Schizomida
9. Whip spider- Amblypygi
10. Ricinuleids- Ricinulei
11. Harvestmen- Opiliones

I'm bumping this in hopes that someone can answer my Question.

the others are

trigonotarbida
phalangiotarbi
haptopoda
pulmonatastem

but they have no extant species.

Pulk said:

the others are

trigonotarbida
phalangiotarbi
haptopoda
pulmonatastem

but they have no extant species.

Click to expand...

Well that makes more since that most books will only put the species that are still alive.