Tuesday, March 27, 2012

Back From the South: Back "To" the South: Finding Cinygmula subaequalis

I wasn't sure where to go this morning, having been out of the streams for a week.  But I chose the South River up in Greene County, and it proved to be a good choice.

A new -- for me -- species of flatheaded mayfly: Cinygmula subaequalis.  When I first saw these -- I found two of them -- I thought I had found some early Heptagenia species.  Heptagenia marginalis, some may remember, is a flathead that I typically find in our streams in late summer.  It looks like this:

But the colors and patterns were not quite right.   So, I preserved one of the nymphs to look at closely using the microscope.  When I did that, I could not see what we need to see on Heptagenia nymphs -- fibrilliform behind each of the gills.  Fibrilliform is the feathery part of the gill that looks like this on a Heptagenia nymph:

Also note in this photo that the final gill of a Heptagenia nymph is smaller than those that precede it.  Now look at the gills on the nymph that I found this morning.

There is no fibrilliform visible behind any gill, and the gills are all the same size.  So, off I went to one of our keys in search of a flatheaded nymph on which fibrilliform is clearly absent.  So I looked in Peckarsky (Freshwater Macroinvertebrates, p. 31) where I read: "Front of head distinctly emarginate medially, maxillary palps normally visible at sides of head from dorsal view; fibrillifrom portion of gills absent or reduced to tiny filaments....Cinygmula."

So, is the head "distinctly emarginate," and are the maxillary palps "visible at the sides of the head" in a dorsal view?   The microscope clearly reveals that the answer is "yes" to both questions.

Let me add from Steven Beaty ("The Ephemeroptera of North Carolina, p. 17) the following things on Cinygmula --

1. "Genus diagnosis: Front of head incised medially; maxillary palpi protrude at side of head; all gills on segments 1-7 similar in size and shape; fibrilifrom portion of gills 2-6 absent or vestigial; three caudal filaments."

2. "In high quality mountain streams.  Collected March -- June."

3. "Cinygmula subaequalis is the only species in NC and is often confused with Heptagenia."

So there you have it.  A new species -- always makes my day.


It was a banner day at the South River, one of those days that I ended up getting home late: too many good insects and too many photos to take.  The dominant insect?  The Perlodid stonefly, Isoperla namata, the leaf packs were crawling with them.  But that was just the beginning, so here we go with some photos.

1. Maturing Isoperla namatas.

2. A gorgeous brushlegged mayfly -- Isonychia bicolor.

3. A maturing green stonefly, genus Sweltsa.

4. Spiny crawlers, of course, both E. dorothea (first) and E. invaria (second).

5. Blephariceridae -- net-winged midges -- both the larvae (on the left) and the pupae (on the right).

6. Another Rhyacophila carolina freeliving caddisfly larva (note the burnt orange head).

7. And the "common" R. fuscula freeliving caddisfly, both larva and pupa.

And finally, two "first of the season" insects --

8. A Nemourid stonefly, genus Amphinemura, the one that is common in our streams in the spring.  Note the "frilly gills" that stick out from the neck.

8. And a Perlodid stonefly, Isoperla holochlora.

When this one grows up, it will look something like this. (note the similar pattern on the head)


"Red buds" in bloom: a sure sign of spring in Virginia. (Streamside at South River)

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