What makes tarantulas unique?

So I've been trying to find the difference between Theraphosidae (tarantulas) and Diplauridae (most funnel web spiders) or other mygalomorph spiders. So far I've found next to nothing. The only thing I found was that Diplaurids tend to have longer spinnerets. If that's true that doesn't seem like much to call for a different family. I've found nothing about other mygalomorph spiders. If anybody knows or has a guess it would be very much appreciated.

I don't know a ton but from what I've gathered there are few things that make it a tarantula. They have to have setae and they use their legs to bite rather than pinching their fangs together. I'm sorry I don't remember the rest but there are 3 or four more things that make Ts. I'll look it up if know one fills in the rest but that should get you started. Spinnerets are another one I think

Roosterbomb said:

I don't know a ton but from what I've gathered there are few things that make it a tarantula. They have to have setae and they use their legs to bite rather than pinching their fangs together. I'm sorry I don't remember the rest but there are 3 or four more things that make Ts. I'll look it up if know one fills in the rest but that should get you started. Spinnerets are another one I think

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The OP was asking what makes tarantulas in particular unique. All mygalomorphs have fangs that point downwards.

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Well, visually they are quite obviously different. For example, you may notice Dipluridae tend to have tapering or pointed legs. The eyes are different. They themselves are often sort of elongated. When I look at the different mygalomorph, each family does look unique in it's own way to me; I can see how they are related, but I have no issue seeing why they are separated.

Realistically though, we're hobbyists, not taxonomists. We can look at them and argue we believe them to be different species (for example, the fact that taxonomically G.rosea and porteri are considered one, but most in the hobby consider them different; same with the subfusca/bara) and that's understandable, because we're around them constantly. But these are separated all the way up at family. There are likely taxonomical reasons we don't have the education or equipment to see.

Belle Fury said:

Well, visually they are quite obviously different. For example, you may notice Dipluridae tend to have tapering or pointed legs. The eyes are different. They themselves are often sort of elongated. When I look at the different mygalomorph, each family does look unique in it's own way to me; I can see how they are related, but I have no issue seeing why they are separated.

Realistically though, we're hobbyists, not taxonomists. We can look at them and argue we believe them to be different species (for example, the fact that taxonomically G.rosea and porteri are considered one, but most in the hobby consider them different; same with the subfusca/bara) and that's understandable, because we're around them constantly. But these are separated all the way up at family. There are likely taxonomical reasons we don't have the education or equipment to see.

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Visually Ephebopus and Avicularia look different, but they're still in the same subfamily. I don't think the obvious features define a difference in such a high extent. What I was looking for was the taxonomical differences either how they are, or dumbed-down.

What you are wanting is a key to the families of the infraorder Mygalomorphae. You will have to do some homework to assemble a key from various research that has occurred for the past 2 decades or so. I can't produce a full key here because it would make for a very large post, but here are characters that make the Theraphosidae distinct from all other mygalomorph families.

- Claw tufts and scopulae present
- Apical segment of posterior spinnerets finger-like (referred to as "digitform" in the scientific literature). In other words, the last segment of the longest spinnerets are long and finger-like
- Distinct lobe present and well developed of the anterior of maxilla (See the references below for illustrations on what this looks like. It's hard for me to describe using plain english other than saying "there is a protrusion on the top of the maxilla.")
- Body hairy (referred to as "hirsute" in the scientific literature

For further reading and for keys to other Mygalomorphae families, see the following resources. All of these have illustrations on what the above characters look like.

The spider infraorder Mygalomorphae (Araneae) : cladistics and systematics. Bulletin of the AMNH ; v. 182, article 1
Raven, Robert J. http://digitallibrary.amnh.org/handle/2246/955
* This is a very important paper to read and study if you are serious about the subject. It is one of the most referenced papers in scientific studies on the Mygalomorphae, including theraphosid, taxonomy.

Baboon and Trapdoor Spiders of Southern Africa: An Identification Manual
A.S. Dippenaar-Schoeman http://ir.nmu.org.ua/bitstream/hand...059978a18d3ec5ef94.pdf?sequence=1&isAllowed=y

Spiders of North America An Identification Manual. Published by the American Arachnological Society. Not available for free online, but can be purchased at Amazon.com
http://www.americanarachnology.org/publications.html#snaim