difference from t's to true spiders

[trivium160]

What is the difference from a true spider to a t?

 

[butch4skin]

The articulation angle of the chelicerae, uh...T's have the twin scopulae claws, which true spiders don't have, I think that's right. There's probably other stuff I don't even know.

 

[lucanidae]

Theraphosids have 4 booklungs, most true spiders have 2. Some true spiders have trachea, no tarantulas do. The list goes on....

 

[AphonopelmaTX]

What is the difference from a true spider to a t?

Try this post in this forum for starters. http://www.arachnoboards.com/ab/showthread.php?t=91084&page=2

As I'm sure you already know, "true spiders" are the Aranea. Can some one tell me what the term "true spider" means anyhow? How is an Araneomorph a more true spider than a mygalomorph?

- Lonnie

 

[problemchildx]

As I'm sure you already know, "true spiders" are the Aranea. Can some one tell me what the term "true spider" means anyhow? How is an Araneomorph a more true spider than a mygalomorph?

Maybe it's cause the majority of Araneae are actually those small, spindly, and usually dubbed "creepy" spiders you secretly want your girlfriend to kill for you but are too embarrassed to ask. I'm sure when kids see the first spider in their life, it will be outside in a web, and they won't be lucky enough to witness the representatives of the mygalomorphae. This is a good question, cause I dunno why they are called true spiders. Why not just spiders? Perhaps Tarantulas liken to the mammals of the spider kingdom. What with superior lifespans, sizes, and diets.

:razz:

 

[Stylopidae]

Simply, yes, a tarantula is a spider because it has 4 pairs of walking legs, two body segments joined with a "waist" called a pedicile, and has silk producing organs.

Characters of an Arachnid:
- Wingless
- Four pair of walking legs
- Two body segments

Characters of a spider (Araneae):
All characters of an arachnid plus
- The two body segments joined with a narrow waist called a pedicile
- Has silk producing organs

Characters of a tarantula (Theraphosidae):
We skipped many taxon to get to the good stuff. This is what separates a tarantula from other spiders:
- Breath using two pairs of book lungs
- Have two claws and scopulae on each "foot" (tarsi)
- Fangs that move up and down

To hit on a point made previously, presence of venom glands in the chelicerae is not a character specific to the araneae. Spiders in the families Uloboridae, Holarchaeidae, and spiders in the suborder Mesothelae lack venom glands.

- Lonnie

I'm gonna elaborate on this post.

First off, the only invertebrates with wings are insects so being wingless isn't really a characteristic of being an arachnid.

Arachnids do have 8 pairs of walking legs, however it's very important to mention that they have eight pairs of legs in the adult stage. Ticks and mites have 6 legged nymphs.

Arachnids actually have 6 pairs of appendages total. The first two are the chelicerae (for most chelicerates, these have been modified into mouthparts, with the exception being horseshoe crabs and maybe sea spiders...don't know a whole lot about those), the second two are the pedipalps.

In male spiders, the pedipalps are modified into sexual organs.

Having two body segments isn't really a characteristic of arachnids...in mites, some ticks and some opilliones, the two segments are fused to make one segment. The cephalothorax is a fusing of the head and thorax segments as found in crustceans.

In assassin spiders, the cephalothorax operates as two essentially independant units.

Having silk producing organs is not a characteristic of spiders alone...many insects and even centipedes have silk glands. Mites, too. The main difference between spiders and the rest of these are the way the silk spinning organs are laid out...I can't really elaborate more on that because I'm not 100% sure how exactly they're different. I want to say it's the fact that the spinerettes are jointed in spiders or that spiders produce multiple types of silk as opposed to one type, but I'm not 100% sure if that's really the case. I need to read up on that.

Here's a website, though. Might be buried in here somewhere:

http://tolweb.org/Araneae/2546


There's some great electron microscopy photos in there, too.

Characteristics of araneomorphs spiders or 'true spiders'

• One pair of booklungs
• Trachae that open near spineretts
• Fangs point towards each other, instead of sloping downward (pinching VS stabbing)
• 6 spinerettes (most mygalamophs have either 4 or 6, while the araneomorphs usually have 6...always exceptions, but this rule *should* hold for tarantulas VS araneomorphs)
• I just discovered how to make bullets...isn't that neat?

True spiders are referred to as such because the mygalamorphs are more primitive than the araneomorphs. The araneomorphs are considered more advanced than mygalamorphs.

Mygalamorphs evolved somewhere near the end of the triassic, while araneomorphs evolved somewhere near the middle of the jurassic.

 

[butch4skin]

Is it true that the closest evolutionary non-arachnid relatives of arachnids are horseshoe crabs and sea spiders?

 

[lucanidae]

I was with you on all of that until here:

Arachnids do have 8 pairs of walking legs, however it's very important to mention that they have eight pairs of legs in the adult stage.

Don't forget that amblypygids, uropygids, schizomids, and some opilionid families have modified legs that serve as sensory organs and can't help walking at all. Wouldn't want to declassify them as arachnids because they don't have four pairs of 'walking' legs.

 

[Stylopidae]

Don't forget that amblypygids, uropygids, schizomids, and some opilionid families have modified legs that serve as sensory organs and can't help walking at all. Wouldn't want to declassify them as arachnids because they don't have four pairs of 'walking' legs.

Well...yeah, true.

What would be a better way to describe those legs?

The way I've been taught was always 'walking legs' and I've always taken a bit of an issue with that (mostly because of the antennaform legs of the amblypygids and uropygids). Just didn't know a better terminology.

 

[lucanidae]

I guess you could call them modified walking legs for sensory use...that would work the walking part back in without saying they can actually be used for walking. Or you could just call them modifiged sensory legs.

 

[M.F.Bagaturov]

Good battle guys!

To answer the question. First of all You should as it was told separate tarantulas as a mygalomorphs from araneimorphs - first step.
And to separate the tarantulas from other mygalomorph spiders.
Th main difficultie is to separate the Tarantula from very close related taxa - barichelidae, which mostly differ in the structure of the spinnerets (silk appendges.
Here, You'll find the general differences: http://tarantulas.tropica.ru/en/node/570#Dif
Following the above discussion You can also find more details

 

[Stylopidae]

Is it true that the closest evolutionary non-arachnid relatives of arachnids are horseshoe crabs and sea spiders?

Yes...horseshoe crabs are considered basal chelicerates. It's actually neat to look at them, because they're trapped in an area of evolution where the legs are just starting to be modified for different purposes. This is readily apparent if you look at the differences between the pedipalps of the males and females, and also looking at the chelicera which are just legs right by the mouth starting to be used as mouthparts.

They're reduced, but they still very closely resemble legs.

I'm not too sure about sea spiders, though. Some scientists consider them part of the chelicerates, and some scientists consider them part of a different phylum. I'm not familiar enough with their physiology to really toss anything relevant in (but I can make a subtle plea to the resident PHDs watching this thread to fill us in ).

http://www.ucmp.berkeley.edu/arthropoda/pycnogonida.html
http://www.dnr.state.md.us/education/horseshoecrab/anatomy.html
http://www.dnr.state.md.us/education/horseshoecrab/malevsfemale.html

MF...would you be able to fill us in on the differences between the spinerettes of spiders and the spinerettes of the other animals I mentioned that spin silk?

 

[AphonopelmaTX]

Thanks Chesire. That was quite a bit of really good info. Although the question is very rudimentary one, the answer is quite complex.

- Lonnie

 

[Thoth]

Another difference I read some where is resistance to dessication, where araneamorphs are far more resistant than mygalamorphs

 

[PhormictopusMan]

Another difference I read some where is resistance to dessication, where araneamorphs are far more resistant than mygalamorphs

Whenever I have attempted to keep "true spiders" I have run in to terrible problems with dessication (except for Latrodectus sp.). Much more so that I do with Tarantulas. But this might just be that "true spiders" need food on a far more regular basis than Tarantulas.

--Chris

 

[Stylopidae]

Thanks Chesire. That was quite a bit of really good info. Although the question is very rudimentary one, the answer is quite complex.

- Lonnie

That's the way it is with most things in life.