Tiny Mygalomorphae (USA Natives)

[cacoseraph]

The recent post on the Microhexura montivaga (Spruce-fir moss spider) ( http://www.arachnoboards.com/ab/showthread.php?t=117703 ) has gotten me thinking about tiny mygs again.


I was wondering what the smallest mygs in the USA were?


I think maybe Hexurella might be small? obviously Microhexura is pretty tiny.

What are the other small ones out there? (bonus points for being in southern california)

 

[cacoseraph]

Hexurella rupicola makes lenticular egg cases that are 1.5-2mm across and contain 4-7 eggs!

i think this might be one of the smallest mygs in the united states

adult female total bodylenth, including chelicerae is 4.5mm!!!!!!
this spider probably has a DLS of under 1cm!!!!



Megahexura fulva total bodylength of mature female (including chelicerae) is 18mm. carapace is 5.6mm long and 4.7mm wide
(in Claremont, Glendora, Los Angeles, Murietta, Idylwild, and many many more places! )




both of these species can be found in Murietta, CA! anyone up for a trip?!


http://digitallibrary.amnh.org/dspace/bitstream/2246/5425/1/N2687.pdf

 

[cacoseraph]

heh. i am working on breeding these now

the female in the mating vid died of some kind of strange molt issue :/

i found a valley full of these things!

i am going over my pics and processing them and making a youtube or two... but for starters, here is a MATURE MALE... and the scale is in CM!

that's a ~2.2cm fairly stretched DLS!


I got what i believe to be 2.2.2 with the 2xx being MM very definite. *I suspect the two females because they are as big or bigger in the ceph than the males, but not bulbed out (no hooks for this species). *The two unknown are much smaller than the other four, with one well under a cm DLS and the other in the 4-5mm DLS range, possibly smaller. *The two unsexed are so small i don't want to risk losing or squishing them with measuring pics.

Right now my plan is to let the females get settled in and then introduce the males to them.

HABITAT

Finding where this species lives is no longer a challenge, as they are all over the valley i hiked. *The real problem is in getting the spider out of its burrow and into your catcher. *While some specimens of good size *were* found under rocks, the big females were in elaborate burrows that wrap around rocks and even worse, roots. *Since even the mature spiders are so small (their cephalothorax is under/around 5mm wide) they can slither into quite small cracks in between rather large rocks... and their escape holes in dirt are very easy to accidentally fill in or obliterate.

It seems like the best catching strategy depends on the time of day. *During high sun you can maximize your chance of bagging a specimen by picking a burrow that appears to be under a largish rock. *If the rock is cleared of any topside debris and dirt and quickly flipped there is a chance you can catch the spider before it can make it to its deep retreat. *When dusk is approaching or on you, it seems like the spiders might lurk their burrow entrances, in somewhat typical myg fashion. *If you can spot a spider lurking you can possibly insert a blade or garden shovel behind the spider, blocking it from retreat... but given the small size of the spider and the rotten substrate i found them it it is risky.


As to the burrows themselves... i am not 100% locked down on how the burrows look.. this could be as a result of a somewhat wide range in the amount of web found outside of the actual "hole"/under ground part of the burrow. *It seems like the bulk of the burrows i spotted did not have a large amount of web outside of the hole... just a very small and easy to miss bit of sheet webbing. *A small percentage of the burrows seemed to have some sheets and a bit of tube web that did extend outside of their burrow. *All the burrows that were confirmed to have M.f's in them had obvious sheet webbing easily visible when a flashlight was shined into the burrow. *Of course, since i didn't really dig out a lot of "naked", non-webbed holes i don't know if this an artifact of my observations or if most of the time the spiders do lay down a lot of web like that. *I suspect they are moderate to high webbers... not quite in the Dipluridae range (webbing maniacs), but definitely more much more profligate than all the USA:CA Aphonopelma burrows i have seen.

Perhaps the most confusing burrow i found might have actually had a M.f. take over the webbing of a Agelenidae grass spider. *I even found what i initially thought was a molt but later realized might have been a husk or bolus of the grass spider remains... when i found that i almost stopped digging out the burrow, but continued and found one of the mature females.

I found both mature males in burrows with a decent amount of webbing laid down. *At the time i thought it was interesting that the males made such permanent looking burrows, but in retrospect i think it is entirely possible that the males were actually just lurking the entrance to a females burrow. *If that is the case, then when a MM is found in a burrow with anything more than cursory webbing the burrow should continue to be excavated... if a female is found than it would certainly lend credence to this theory.

The best way to describe a fulva burrow's webbing is that it is diaphanous. *It is more diaphanous/finely woven than grass spiders, to appearances to me. *Of course, i don't have the best eyes in the world and someone else might choose to describe it differently... but that is the word that has stuck in my head for a while now.

Here is a fairly typical burrow entrance:

zoom --> http://i21.photobucket.com/albums/b287/cacoseraph/mygla/mecico/Megahexura/fulva/burrow_entranceb.jpg

and a burrow with a female lurking the entrance:

zoom --> http://i21.photobucket.com/albums/b...mecico/Megahexura/fulva/somebody_is_homeb.jpg


you can read more about M. fulva in the species thread here: http://scabies.myfreeforum.org/about921.html


TAXONOMY
I am working off of the assumption these are Mecicobothriidae, because of their very long spinnerets. *I am working off of AMERICAN MUSEUM
Novitiates Number 2687: A Revision of the Spider Family
Mecicobothriidae (Araneae, Mygalomorphae) by WILLIS J. GERTSCH AND NORMAN I. PLATNICK
using their Key to genera for Mecico's:
1. Abdomen with separate anterior and dorsal tergal
plates (as in fig. 37); anterior lateral spinnerets
two-segmented (as in fig. 52) .............2 * <--- YEP (range and see pic)
Abdomen with anterior and dorsal tergal plates
fused into single scutum; anterior lateral spinnerets
one-segmented (fig. 59) or absent (fig. 68 ); Oregon and Washington ....... .Hexura * <--- NOPE, range

you can just make out the fact there are two plates

2. Posterior lateral spinnerets three-segmented (as in
fig. 36) ......................... 3 *<--- looks like it, see pic
Posterior lateral spinnerets four-segmented (fig.
71); Arizona, California, and Baja California
....Hexurella *<--- nope, WAY too big, too

lines indicate divisions between segments


3. Cephalothorax with pronounced pleurital extensions
at posterolateral corners (figs. 51, 53);
California .................... Megahexura * <-- yep (range, that characteristic is hard to get a pic of... the spider has to have no flex "up" in between abdomen and ceph)
Cephalothorax without pronounced pleurital extensions
at posterolateral corners (fig. 35);
Argentina ................. Mecicobothrium *<-- neg, range

MATING

Mating Megahexura fulva, Tawny Dwarf Tarantula

tinyfi *http://www.youtube.com/watch?v=DftVkUI0aVA
lofi http://www.youtube.com/watch?v=oO4mr3v2B3U
hifi http://www.youtube.com/watch?v=frH4v1EfVZo


Etymology
Megahexura fulva

Megahexura:
mega prefix added to existent Hexura genus name. *mega means big/giant, as Megahexura about about twice as big as Hexura spiders

Hexura
Hex- prefix means six
-ura means tail http://www.myetymology.com/latin/Brachyura.html

fulva means tawny (which means kind of golden yellow brownish) http://www.myetymology.com/latin/fulvus.html

so, Megahexura fulva spider means tawny giant six tail spider




(i'm going to edit this post, i am using it to get myself like, organized and what not)

http://scabies.myfreeforum.org/about4363.html

 

[KUJordan]

Man I don't know what the smallest would be. That one you posted seems like it'd be it. I found this guy in Mendocino county, CA last year when I accidentally broke apart a rotten log. She had actually burrowed into the rotten wood of the log. It was just a very lucky break I guess, literally:

Not sure of her species, but dang she was small. I don't know if she was mature or not either. She wasn't a purseweb, as I've seen many of those and she looks nothing like them. I'd say she was easily less than 1cm in total body length:

Maybe Hebestatis sp?

-Jordan

 

[What]

Maybe Hebestatis sp?

You know...if it was from SoCal I would say that for sure... but Im thinking that there is some other Hebestatis looking type of trapdoor found up north a bit... Oh well...

I would say it is almost definitely Hebestatis anyway, though.

 

[MaartenSFS]

Wouw, you are more persistant than most scientists, I imagine. I think you should change your job. Anyways, those are awesome. I can't believe the diversity in the U.S and most species aren't even well-documented. I thought that everything would have been found by now and field guides published. I can't wait to move further south and join the hunt!

When I was trying to dig out small Macrothele sp. I would first start by sticking the small shovel behind the lurking spider and then digging well around the hole until I could pull the tube out. Usually I would find the spider curled up somewhere in there, but I had to be careful not to get bitten because there are some very toxic spiders in the genus and China is quite undocumented. Road cuts had plenty of the obvious funnel webs and I was traveling by motorcycle so it was easy to stop and go.

Sometimes I would find tubes near or under rocks and I just dug well around the hole and did the same thing but road cuts were far better options. Roots would be terrible! Find some new species and name it "Genus cacoensis" or something (I'm not a taxonomist, so..).