Autor Thema: Trochosa terricola? => Trochosa robusta  (Gelesen 944 mal)

Frits Broekhuis

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Trochosa terricola? => Trochosa robusta
« am: 2017-11-26 21:47:06 »
Found this one in the south of Germany (near Engen) in July. It turned adult a couple of weeks ago. I think it resembles Trochosa terricola, but I'm not sure. Do you agree?

[2017-07-30-i]
« Letzte Änderung: 2017-11-29 19:18:20 von Frits Broekhuis »

Tobias

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Re: Trochosa terricola?
« Antwort #1 am: 2017-11-26 22:14:34 »
it has a palpal claw  :D

Frits Broekhuis

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Re: Trochosa terricola?
« Antwort #2 am: 2017-11-26 22:31:25 »
it has a palpal claw  :D

Eh, okay, thanks for mentioning that ;-)

So I guess robusta or ruricola? I guess it must be ruricola then, because the spider is rather small for robusta, KL=9mm. Do you agree?

Frits Broekhuis

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Re: Trochosa terricola?
« Antwort #3 am: 2017-11-26 22:44:41 »
Hm, but the first pair of legs do not have the darkening from tibia down (see picture below), so ruricola is also wrong?

And for robusta, the palp does not match...

Tobias

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Re: Trochosa terricola?
« Antwort #4 am: 2017-11-27 14:36:38 »
T. robusta-males can be 9 mm, that's quite common. The palpal claw is small and not large and robust (like in ruricola), and the leg I seems only to darkened at the region of the tarsus. The position of sklerites and other parts of the palp are very similar in alle Trochosa-species, important is the claw, the cymbium and in spinipalpis the spine tufts.
 What was the habitat of this spider? If you say it was dry and warm...

Frits Broekhuis

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Re: Trochosa terricola?
« Antwort #5 am: 2017-11-27 20:24:59 »
Okay, thanks, I'll check my records and report back later!

Frits Broekhuis

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Re: Trochosa terricola?
« Antwort #6 am: 2017-11-27 22:22:05 »
I'm still stuck on this one. I think it cannot be T. robusta, because the palp does not fit at all. The other species are a better match for the palp.

So I sort of concluded it must be ruricola, but that species has a hump on the bottom of the cheliceral fangs (see araneae), and mine does not seem to have one.

As for the habitat, the spider was found during a hiking trip in the surroundings of the southern German town of Engen. It was very warm at the time, but it wasn't particularly dry.

Arno Grabolle

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Re: Trochosa terricola?
« Antwort #7 am: 2017-11-28 07:55:33 »
I guess it is robusta. The overall look of your specimen is much more robusta like.

Arno

Pierre Oger

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Re: Trochosa terricola?
« Antwort #8 am: 2017-11-28 09:31:49 »
Imho the palp is clearly in favour of T. ruricola : the palpal claw is 'big' and the embolus fits better with T. ruricola...

Tobias

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Re: Trochosa terricola?
« Antwort #9 am: 2017-11-28 10:02:29 »
Mmh, For me the palpal claw is not so big and robust like e.g. in

http://arachno.piwigo.com/picture?/6945/category/643-trochosa_ruricola
http://arachno.piwigo.com/picture?/19793/category/643-trochosa_ruricola

and seems more similar to e.g.
http://arachno.piwigo.com/picture?/14368/category/965-trochosa_robusta

In my opinion the cymbium is also not that roundish at the tip and bend as in in T. ruricola

(I've seen that we don't have good palpal pictures of both species in the wiki!)

How does the other palp look?

Tobias


Frits Broekhuis

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Re: Trochosa terricola?
« Antwort #10 am: 2017-11-28 10:29:43 »
Thanks for your help!

What confuses me is that on Pierre's site, there are some palps that resemble mine a bit, but some others that look quite different:
 
This one resembles mine: http://arachno.piwigo.com/picture?/9813/category/965-trochosa_robusta
And this one looks very different: http://arachno.piwigo.com/picture?/20313/category/965-trochosa_robusta

The palpal drawings on areneae suggest it is not robusta.

Does anyone have experience with using the chelicerae as means of determination? According to araneae, there is a clear difference between the fangs of robusta and ruricola. Ruricola has a hump on the fangs (visible from front), and robusta does not. I inspected the fangs of my spider and found no hump, but a nice rounded shape (as is normal for most spiders).

When I'm back home this evening, I can try to make some more pictures.

Tobias

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Re: Trochosa terricola?
« Antwort #11 am: 2017-11-28 10:42:52 »
Thanks for your help!

What confuses me is that on Pierre's site, there are some palps that resemble mine a bit, but some others that look quite different:
 
This one resembles mine: http://arachno.piwigo.com/picture?/9813/category/965-trochosa_robusta
And this one looks very different: http://arachno.piwigo.com/picture?/20313/category/965-trochosa_robusta

The palpal drawings on areneae suggest it is not robusta.

Does anyone have experience with using the chelicerae as means of determination? According to araneae, there is a clear difference between the fangs of robusta and ruricola. Ruricola has a hump on the fangs (visible from front), and robusta does not. I inspected the fangs of my spider and found no hump, but a nice rounded shape (as is normal for most spiders).

When I'm back home this evening, I can try to make some more pictures.

Hi Frits,

I don't have a complete literature overview, but the character you mentioned is also one the main features to distinguish both species in Locket & Millidge. I will check some specimens here at SMNK and will report.

Tobias

Pierre Oger

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Re: Trochosa terricola?
« Antwort #12 am: 2017-11-28 12:39:31 »
Hi all,

@Frits: you are right ! The first link you mention refers to a T. ruricola : I thus deleted those pictures...

I also made a comparison with the chelicera and the tip on cymbium of both species : picture is here : http://arachno.piwigo.com/picture?/30201/category/965-trochosa_robusta

NB : picture can be used in the Wiki  ;)

Tobias

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Re: Trochosa terricola?
« Antwort #13 am: 2017-11-28 13:42:25 »
I've examined some material determined by myself (6 males of T. robusta, 7 of ruricola) from 3 different Locations and the character seems stable in all specimens.

It's interesting that this specimen is ruricolam even though the coloration is very robusta-like. it shows how one could be mislead just by fotos. Thanks to Pierre for pointing in the right direction.

Tobias

Arno Grabolle

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Re: Trochosa terricola?
« Antwort #14 am: 2017-11-28 19:14:10 »
But didn't Frits wrote, that his specimen has no hump on the cheliceral fang?

Arno

Frits Broekhuis

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Re: Trochosa terricola?
« Antwort #15 am: 2017-11-28 21:50:09 »
That's right Arno, here is a ventral view of the right chelicera. No hump at all on the fang.
« Letzte Änderung: 2017-11-29 22:15:56 von Frits Broekhuis »

Frits Broekhuis

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Re: Trochosa terricola?
« Antwort #16 am: 2017-11-28 21:59:34 »
I guess it must be T. ruricola without the hump. I took another set of pictures of the left palp and this one is a very good match with this palp picture fom Pierre's site.

Interestingly, on the araneae site it says:

Chelicerae male: fang mostly with hump on ventral side.

Frits Broekhuis

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Re: Trochosa terricola?
« Antwort #17 am: 2017-11-28 22:02:18 »
Here is another ventral shot, and a shot of the claw:

Frits Broekhuis

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Re: Trochosa terricola?
« Antwort #18 am: 2017-11-29 08:40:37 »
@Tobias: thanks a lot for your research!

My final conclusion would be that this is indeed T. ruricola, does everyone agree?

Tobias

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Re: Trochosa terricola?
« Antwort #19 am: 2017-11-29 15:04:05 »
But didn't Frits wrote, that his specimen has no hump on the cheliceral fang?

Now I'm totally confused. I somehow read it has a hump on the chelicerae. I guess, then it is a robusta. The claw does not look different on other pictures. I've examined some other males (abot 20), and in all specimens without an exception the hump was visible in T. ruricola and missing in T. robusta, so I think it is a good feature for separating both species. I've marked the area where the palp shoud be much bulky compared to the one of Pierre.

Thanks Arno.

Tobias

Frits Broekhuis

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Re: Trochosa terricola?
« Antwort #20 am: 2017-11-29 19:17:50 »
Hm, I was sort of convinced it wasn't robusta because the palps on Pierre's site look quite different. But I guess the palps of all the European Trochosa species are rather similar, and I don't have any experience comparing them.

It is also rather reassuring that Arno thinks the spider looks more like T. robusta ;-) Also, the legs are indicative of T. robusta (no darkened tibiae like ruricola).

Thanks again Tobias, for your effort. It would be convenient to have this information in the wiki (with claw and hump -> ruricola; with claw, no hump -> robusta).


Arno Grabolle

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Re: Trochosa terricola? => Trochosa robusta
« Antwort #21 am: 2017-11-29 22:00:39 »
In my opinion T. robusta stands out of all European Trochosa species. The differences are not very noticeable, but I think, I can see it on most pictures. T. robusta is slightly elongated and has a wide head region with almost parallel sides. The prosoma bands are strong and well covered with light hairs. The legs are more grayish (not as yellow) and the tarsus of leg one is obviously thickened.

I think the compare picture brings it to the point ...

Trochosa-males.jpg
*Trochosa-males.jpg (135.55 KB . 820x1406 - angeschaut 121 Mal)

Arno

Tobias

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Re: Trochosa terricola? => Trochosa robusta
« Antwort #22 am: 2017-11-30 11:39:23 »
Good observation, thanks.

I will try to include some of the info in the wiki.

Tobias

Rainer Breitling

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Re: Trochosa terricola? => Trochosa robusta
« Antwort #23 am: 2017-12-04 14:40:09 »
Ich habe diese Diskussion mit grossem Interesse verfolgt. Ich hätte nicht gedacht, dass die Pedipalpen hier keine Identifizierung erlauben; die Abbildungen bei araneae.unibe.ch sehen so deutlich verschieden aus, und auch Pierres Fotos von T. robusta haben diese auffallende Medianapophyse. Aber schon Engelhardt hatte festgestellt, dass die üblichen Merkmale in dieser Gattung nicht weiterhelfen. Auch der Zahn auf den Chelizerenklaue ist übrigens nur bedingt hilfreich: Engelhardt schreibt, dass er bei etwa 10% der T. ruricola-Examplare spurlos fehlt. Die Färbung der Vordertibien scheint zusammen mit der Cymbiumklaue das entscheidende Merkmal zu sein, unterstützt von den subtileren Unterschieden, die Arno illustriert.
Beste Grüsse,
Rainer

Tobias

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Re: Trochosa terricola? => Trochosa robusta
« Antwort #24 am: 2017-12-05 00:23:49 »
10% erscheinen mir recht viel. Das wäre ja jedes zehnte Tier. Die Tiere bei uns in der Belegsammlung wurden sehr wahrscheinlich nach dem Palpus bestimmt, daher fällt der Fehler "kein Höcker, keine ruricola" raus. Ich habe inzwischen 30 Männchen von ruricola rausgesucht, alle mit recht deutlichem bis sehr deutlichem Höcker.

Mhh, ich glaube, es wäre mal interessant große Aufsammlungen aus drei oder vier Feldstudien anzuschauen. Das haben wir im Museum. Ich melde mich wieder, wenn ich mehr weiß.

Ich muss zugeben, für mich war der Palpus von Anfang an klar robusta, ich bin bei Bildern aber immer vorsichtig(er).

Tobias