No, not quite. Both hold their chelicerae in about the same postition when at rest. Fangs may face different directions, but don't necessarily cross in true spiders. The picture below is the only one I had handy at the moment that showed the position of the chelicerae of a true spider, in this case an Arizona brown spider (or recluse or violin spider or whatever other name you like - Loxosceles arizonica). Notice that they are held in the l l position that Brachy mentions. However, when they are used for catching prey, they move sideways in a pincer movement, rather than the "overhead stab" that tarantulas use. However, Brachy is close in his description. In some cases the tips of the fangs themselves may cross. But that isn't a reliable feature - and not the defining one. It's the lateral pincer-like movement that is the key feature. In Spiders of North America: An Identification Manual they separate Mygalomorphs from other Opisthothelae (which includes all spiders except for mesotheles) by "Cheliceral Orientation". There may be other differences, such as book lungs, etc., but the chelicerae are the defining feature.
Simple question. Complex answer. Theraphosid tarantulas (the spiders we call "tarantulas" in the vernacular) are a subgroup of a much larger group called collectively the Mygalomorphae, the mygalomorph spiders. These in turn are a subgroup of the spiders, classified as the Araneae.
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That's a simple question - but with a lot of "correct" answers. First off - not all spiders have the same number of eyes. While most have eight eyes, there are some (such as Loxosceles) that have six eyes, some have two eyes ( such as some caponids) and some that have no eyes (cave dwelling forms, for example). In some spiders, all eyes serve the same purpose - just take advantage of having more of them. Others, such as jumping spiders like Phidippus, assign different functions to different pairs of eyes. Maybe a description of how jumping spider eyes function will help partially answer your question.
Many, but not all do. Caponids, for example are araneomorphs and they do not have book lungs.
Do you know of any scholarly sources or sources by arachnologists that match what you have said about mygalomorphs still being spiders? I am having a discussion with a friend about this, and they are basing their claim of tarantulas not being spiders on the statement by an entomologist professor of theirs, so I'd really like to have some sources of similar academic validity to respond.
Araneae is an order of arachnids which we call "spiders".
I know that, and told my friend that, but because their professor said that tarantulas aren't "true" spiders, this friend now interpreted that to mean that they aren't real spiders, and believes it because their professor is an entomologist, so I am looking for scholarly sources or statements by arachnologists that mygalomorphs are still real spiders, despite the terminology of "true spider" for araneomorphs.
I don't understand what the difficulty is with this professor in understanding that the arachnid order Araneae are the true spiders- thus tarantulas and other mygalomorphs are also true spiders- given that other arachnid orders have a common name which includes the word spider. However, I do understand the need for an authoritative source to support a claim. My suggestion is to head over to the web site of the American Arachnological Society (americanarachnology.org) and use their "Ask a Question" page to get an answer from a specialist. I can't think of a single scholarly source that uses common names, like "true spider", to refer anyone to.