Sunday, August 14, 2011

Two More Species of Small Minnow Mayflies (Baetidae)?

On Thursday, 8/11, I posted this photo of a small minnow mayfly I had just found in the Moormans, noting that I was unsure of the species ID.  Having done some research this morning and looked closely at this nymph using my microscope, I now think I know what it is -- and "think" is the operative word.  In fact, I now think I found two new species of small minnow mayflies in the Moormans last week: Heterocloeon petersi -- pictured above -- and Baetis flavistriga, pictured below.

Let me first make the argument for Heterocloeon petersi, which, I have reason to believe, is uncommon.
My source notes a number of things for ID that require a more powerful microscope than I possess, so I have to focus on features that I can see.  1) As with many -- but not all -- Heterocloeon species, petersi nymphs have "procoxal gills".  This nymph clearly has them.

2) The abdominal segments are grey or grey/brown with "light" margins, and there is no dorsal pattern.   These features show up very well in this photo.

3) It's also worth noting that nymphs of this species are fairly large, and this one measured about 7mm in length, excluding the tails.  (That's big in the "Baetidae" world.)

Now, I remind everyone that I'm an "amateur" here -- I cannot be sure of my ID.  But, for the moment at least, H. petersi would be my guess.  Another look.

Now on to this little fella (no gender ID intended!).

This nymph is tiny -- but B. flavistriga nymphs do not get very big (4-6 mm).  The caudal filaments (tails) on B. flavistriga nymphs have a dark medial band, which is clear from the photo -- but that's fairly common with Baetis species.  So, my proposed ID is only based on the one distinguishing feature that I can discern:  there should be two "kidney shaped spots" toward the bottom edge of each abdominal tergite (segment).  I think I see them.

Based on what I can see -- there are features of the labial palpi that I don't know how to recognize -- I'd suggest that this is a Baetis flavistriga nymph.  But as with the H. petersi identification, this is hypothetical, and if a reader can confirm these ID's or disprove them, I'd be grateful for the help.

Should these ID's prove correct, then these two species of small minnow mayflies must be added to the "small minnow mayflies of summer" discussed in my entries of 8/6 and 8/8.  Below, another look at, possibly, H. petersi.

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