Moving my Cryptaranea atrihastula & subcompta IDs back to genus level.
Long story short, I am not confident in my C. atrihastula or subcompta IDs so have started moving them to genus.
According to Court & Forster (1988) these two can be told apart only by web situation and genital examination, although it might also suggest that if it's not a green splotchy critter but is cryptic, then it's more likely subcompta. However, your mileage may vary on that!
Web-wise, C. atrihastula webs are stretched vertically. According to Court & Forster (1988) p93:
"The snares are striking elongate structures extended both above and below a central orb so that they are usually about three times as high as wide. They are usually constructed parallel to a treetrunk and set off from the bark by a short distance of about 1-3 cm."
And from p96 regarding C. subcompta:
"In contrast to C.atrihastula it seems to be able to occupy more exposed conditions. The web is a typical vertical orbweb which is constructed between twigs of branches and if associated with a treetrunk is normally placed at right angles to it. The dragline usually extends out from the hub and the spider rests on lichen or moss covered bark during the day."
You can also see some pictures in the source document, figures 490-491 and 499-500.
The source doc is available at the WSC site (you'll have to register).
https://wsc.nmbe.ch/species/3524
If you know of other diagnostics, please let me know in the comments :)
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Hi Russell, I found and reviewed the Court and Forster source last year (or thereabouts), and thought I had the diagnostics down. For me, the most striking feature of C. atrihastula is the three dark triangles on the carapace, which C. subcompta are not supposed to have, or at least not as bold. I have seen both C. atrihastula (with the dark markings and web parallel to tree trunks) and "other" species nearby, and the web position and the markings do seem to be consistent with the descriptions. I say "other" species because I am less confident at visually distinguishing between C. subcompta and C. venustula.
C. atrihastula: “Both male and female are similar. The general appearance is mottled green. The carapace is usually greenish but clothed with white hairs which partly obscure the colouration. There are always three black markings; a median band behind the fovea and a pair of reniform marks in front on the mid lateral surface. Although the intensity of the green pigment on the abdomen varies from specimen to specimen and may in some be yellowish, the basic pattern is the same (Figs. 472, 473). There is a broad triangular patch on the anterodorsal surface from which a narrow band passes back down the median surface. The secondary pigmentation may range from black to chocolate or reddish brown” (Court and Forster, 1988).
C. subcompta: “Most of the specimens examined are mottled green but some specimens may be predominantly brown or occasionally almost black. There is generally a distinct patch on the antero-dorsal surface of the abdomen which may be pale green, white or occasionally brick red. The carapace bears markings similar to atrihastula but the anterolateral patches are narrower” (Court and Forster, 1988).
From now on I will also make note of the web (on the web ;-)).
It’s a shame that Mark T is no longer on iNat – he was good at these IDs.
Hope this helps.
Dougal.
Thank you - that's really helpful!
Hmm, just reviewing it again now...so:
The three carapace markings are narrower in subcompta but still always present.
The red/white/green patch on the front of the abdomen is usually there but not always.
If the critter isn't green, it's more likely subcompta but could also be venustula if black or brown.
I'd say on that basis that the carapace feels like a safe bet, and overall colouration might not be too bad to discount atrihastula, but not to confirm another species. I've actually been obsessing on abdomen markings far too much. I will obsess on other features instead ;)
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