Sunday, June 24, 2012

Heterocloeon curiosum at the Rivanna -- but Some New Small Minnow Mayflies as Well

I've been having trouble finding small minnow mayflies in most of the streams that I visit in the winter and spring: no problems today at the Rivanna.  The Rivanna has been too high and off color for me to explore until now.  But I could finally get in and look for some insects today.   I saw three or four small minnow mayflies on the first rock I picked up, including the one in the photo above -- Heterocloeon curiosum.

This is a common small minnow in the Rivanna in summer; it's a species I hardly see anywhere else.  You might recall from last summer that the distinctive trait of this species is the pair of forecoxal/procoxal gills.  These:

Also distinctive is the dorsal pattern: most tergites are brown, with 4 and 10 being pale yellow.  We have a good view of that in the photo below.

I can't say for sure that "sternal tracheation" -- note the gray tracheation on the mesosternum in the microsocope photo above -- is also a species characteristic, but it's something I normally see.  Using size, forecoxal/procoxal gills, and sternal tracheation for definition, the three nymphs pictured below were also H. curiosum.  But if that's true, I sure find the colors more than a little bit odd.  (Well, number three might be all right.)

I think these require more work.

But I found more than H. curiosum this morning.  Another small minnow that was easy to pick out by the tails -- a Baetis intercalaris.


And now we turn to the unknowns.  I found three additional small minnow mayflies this morning that, so far, I have not ID'd, and I think they are three different species.  Since I see no procoxal gills on any of them, they are probably Acentrella or Plauditus nymphs in terms of the genus.  But at the moment, that's all I can tell you -- well, except that all three were small,  3-4 mm.  Here they are.

Mystery Baetid 1:  This one was fairly mature and had banded cerci. 4mm

Mystery Baetid 2: Cerci (tails) on this one were missing.  4mm

Mystery Baetid 3: The smallest of the lot -- only 3 mm in length.

The lab work on these may take me awhile.  If I'm successful I'll be sure to post my results.

Finally, a special treat for me today: the first Calopterigidae of the season -- a "broadwinged damselfly."
I didn't keep it so I can't be sure of the genus.  But the broadwingeds that I found last year were all Haeterina.

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