Tarantula VS True Spiders

[Cheo Samad]

I need help understanding one of the differences between Ts, and true spiders. I understand one of the major differences is the range of motion in the fangs.

To my understanding, (for the sake of example lets just assume you were looking at the spider top down and it's facing forward away from you so its fangs are the furthest from you) the can move their fangs in and out (away from their body forward and hugging them toward the abdoment) as well as pull them apart from the center (like a weird pair of scissors)

My confusion comes when speaking of how true spiders can move their fangs, all of the descriptions I read are very vague on what their increased range of motion is. Is it as simple as they can rotate their fangs inwards and outwards so that the tips of them can come together and pinch and vice versa? I know this is a dumb question, but I've been having trouble finding the answer I'm looking for.

 

[Moakmeister]

Basically tarantulas are Mygalomorphae, a group of spiders who have fangs that point backward. Araneomorphae have fangs that point toward each other. I never really understood this, though, because tarantula fangs point inward in resting position, and they can in fact point their fangs almost totally toward each other when biting prey. Basically the gist of this is that tarantulas are a more primitive line than other spiders. As for the whole "true spider" thing, I don't have a darn clue. Tarantulas ARE spiders. The family is literally in the Araneae order. They're spiders.

 

[Moonohol]

Basically tarantulas are Mygalomorphae, a group of spiders who have fangs that point backward. Araneomorphae have fangs that point toward each other. I never really understood this, though, because tarantula fangs point inward in resting position, and they can in fact point their fangs almost totally toward each other when biting prey. Basically the gist of this is that tarantulas are a more primitive line than other spiders. As for the whole "true spider" thing, I don't have a darn clue. Tarantulas ARE spiders. The family is literally in the Araneae order. They're spiders.

True spiders are members of the infraorder Araneomorphae while tarantulas, along with trapdoor and funnel web spiders, are members of the infraorder Mygalomorphae. I don't think it really means they're any more "true" than tarantulas though.

 

[Ungoliant]

Mygalomorphs, the group that includes tarantulas, are sometimes often called "primitive spiders," and araneomorphs, the group that includes most other spiders, are often called "true spiders." However, they are all spiders.

Certain mygalomorph traits are considered more "primitive," because they appeared early in the evolution of spiders and haven't changed much from those of early spiders. Certain araneomorph traits are deemed more "advanced," because they appeared more recently and have undergone notable change from ancestral traits. However, you can't really say that araneomorphs as a whole are "more advanced" or "more evolved" than mygalomorphs, as they are both equally separated in time from the common ancestor of spiders.

Basically tarantulas are Mygalomorphae, a group of spiders who have fangs that point backward. Araneomorphae have fangs that point toward each other. I never really understood this, though, because tarantula fangs point inward in resting position, and they can in fact point their fangs almost totally toward each other when biting prey.

Think of it more in the way the jaws and fangs move when in use. Mygalomorph fangs move in parallel, swinging up along an arc before a strike.

Araneomorph fangs move in opposition to each other, resembling pincers. Some good illustrations that show the difference:

 

[Cheo Samad]

That picture and explaination just summed it up better in 30 seconds than an hour of reading last night did! Thank you so much.