Wednesday, April 17, 2013

And another new species at Buck Mt. Creek: common stonefly, Paragnetina fumosa

One week, two new species: pretty exciting!  This always happens when I'm convinced that I've seen every species in our streams that I'm going to see.

Common stonefly (Perlidae) -- Paragnetina fumosa.  Paragnetina nymphs have a pronounced spinule row on the occipital ridge, usually lack anal gills, and are "usually distinctly patterned" (Steven Beaty, "The Plecoptera of North Carolina," p. 18).    Beaty describes P. fumosa in the following way (p. 18):

P. fumosa -- nymphs ?? mm; frons with a pair of yellow spots lateral to the median ocellar spot, median ocellar spot often congruous with pale yellow transverse band near labrum; thoracic nota with complex and extensive pattern of yellow markings; yellow femora with one sometimes two distinctive dark brown transverse bands; abdominal terga 3-4, 5 with a pair of pale markings and 8 and 9 mostly pale; anal gills present or absent.  Common and widespread except for Slate Belt and outer Coastal Plain.

I'll use two photos to point out all of those features.  The yellow spots on the frons and the distinctive markings on terga 3-5 and then 8-9 seem to me to be crucial.  (Click on photo to enlarge.)

In this second photo, I've pointed out the dark bands on the rear femora as well as the transverse band near the labrum with which the median ocellar spot is congruous.

Paragnetina fumosa -- no doubt about it.  This is a fairly tolerant Perlid with a TV of 3.6.  This nymph was about 10 mm, but note that it is not yet mature.


Other photos:

1. A fairly mature Perlodid stonefly, Isoperla namata.  The colors were very rich, and I wish I had had better sunlight to get better pictures.

2. That little spiny crawler in the bottom right of the picture (4.5 mm) was the first Drunella I've seen so far this season: Drunella tuberculata.

3. A very colorful Ephemerella invaria spiny crawler.  E. invaria and E. dorothea clearly overlap, since Buck Mt. Creek -- like a lot of our streams at the moment -- is chock-a-block full of E. dorotheas.  If you look closely you can see the tubercles on the posterior edges of the terga (light dots).

4. A fairly mature Helopicus subvarians nymph (Perlodid stonefly).  I saw quite a few.  Black-tipped wing pads.

5. And I was happy to find another Isoperla davisi, even though my photos this time were not very good (couldn't get this one to stop in the tray).


We have seen Paragnetina common stoneflies before, but the species we've seen previously was P. immarginata, also a beautifully patterned nymph.  (7/6/12, Rapidan River)

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