Rats! Just lost another half hours worth of work due to some &#$ software glitch. I'll try to recap
Seeing that my came up, I'll allow myself to comment
Quote:
Originally Posted by Action_Man  I hope its Nemastoma bimaculatum, if it isent Arp`s going to kill me, or is it N. lugubre ? .. |
Nah, no worries, this is
very confusing stuff - and difficult, and small - so I wouldn't want to say anything with too much certainty about this one either
The thing is this: The two species
Nemastoma bimaculatum and
Nemastoma lugubre have been dreadfully confused for some two centuries and the situations has only been cleared up (sort of?) in the past few decades. The fact that both species, as interpreted now, are credited to ancient authors (
N. bimaculatum (Fabricius, 1775);
N. lugubre (Müller, 1776)) reflects the hard work that has gone into interpreting old literature and collections, mainly by Gruber & Martens (1968),
not any sense of clarity since the animals were named/described.
In continental Europe
N. bimaculatum has a (south-)western distribution and
N. lugubre a (north-)eastern one with fairly little overlap. In this picture Britain would fall into the
bimaculatum range and indeed it is (was?)
assumed that this is the only species of the two present in Britain. Incidentally that is part of the reason for leaving the credit for the species with Fabricius, as his original description of
Phalangium bimaculatum lists "Anglia" as the locality.
Nevertheless, following some early 20th century publications by Roewer that handled them as one, many authors have listed and described
N. lugubre for Britain. Interestingly some of these even give characters in the description that would fit
N. lugubre much better than they do
N. bimaculatum. In my view this can mean one of two things:
- The authors copy-catted the descriptions from other (eastern) European authors and didn't look at the British material closely enough.
- The authors indeed did accidentally have (an extremely rare?!) N. lugubre from Britain at hand when they wrote/checked their description.
The best I could do (to date) in finding information about (the true)
N. lugubre in Britain however is this remark from the newsletter of the Opiliones Recording Scheme
Ocularium No.1, 1998 Quote:
|
The latter (=N. lugubre) is not recorded in Britain but there is a chance that it has been overlooked, particularly in eastern regions
|
That's all. Neither the
checklist that John Partridge kindly made available to me, nor the
NBN Gateway list the species for Britain.
So, there it is ... after all that, it's probably best to assume
Nemastoma bimaculatum only in Britain, until proven beyond any doubt that we're looking at something else.
Having said that, the animal
does look like it
might be
N. lugubre but I'm not very apt at recognizing the two from habitus alone.
The thing with the white/silver spots is this: They
are quite variable(!) However, Dutch and Belgian experts have worked out that the indentation of the outside edge is a good "field character" - quite reliable for quickly separating the two in the field: "Strongly indented" =
bimaculatum, versus "mostly continuous (but somewhat jagged)" =
lugubre.
On this animal, but also on
the one Action_Man photographed the indentation is not very clear - I'd say "weakly indented" (illustrated by Action_Man's ID of these as
lugubre 
). This might just mean that the variability in British animals is different than that of continental European ones and that the character is maybe a tad less useful here (!) But, yes, it
could also give reason to having a closer look with a slight suspicion of
lugubre lingering in the back of our heads - finding/confirming
N. lugubre would certainly be
very interesting 
Unfortunately, the characters needed for "proper" ID are quite hard to photograph properly, let alone to recognize from 'general purpose' shots of the animal. There is some slight difference in habitus, especially for the females, as the 'abdomen' is dorsally flatter on
bimaculatum and more rounded on
lugubre, but I still find that hard to recognize from the 'accidental perspectives' that photos provide.
Other than genitalia we might look at the following:
MALES- Shape of the palpal tibia, best evaluated laterally.
- Shape of the apophyses on the distal end of the 1st chelicera segment, best evaluated dorsally (see here or here)
- (shape of penis)
FEMALES- Habitus of opisthosoma ("abdomen")
- Denticulation on opisthosoma (weaker on bimac)
- Denticulation on dorsal side femora of 4th legs (stronger on bimac)
- (length of setae on ovipositor)
For a more comprehensive explanation and some images see:
Meidell, B.A.; Stol, I. (1990) Distribution of Nemastoma bimaculatum (Fabricius, 1775) and N. lugubre (Müller, 1776) (Opiliones) in Norway, with a discussion on “east-west pairs of species”. in Fauna norvegica, Ser.B., Vol.37, pp.1-8. -
PDF (good read!).
So, this animal should probably be treated
N. bimaculatum unless nutmeg runs out and finds a few more to make superb macro images of the details outlined above and/or collects some (in alcohol) to have them "properly" ID'd.
That's all for tonight
Cheers, Arp
. Nevertheless, I'll definitely keep my eyes open for them and try the alcohol method suggested - not sure my photographic skills are quite up to the level of detail needed! 
Linear Mode
