I found this little mayfly at the Rapidan River on Tuesday, and when I looked at it in the bowl, my first guess was that it was nothing but the small minnow mayfly, Baetis intercalaris. Still, something wasn't quite right. It was only when I focussed in to get some photos that I realized this was something I'd not seen before. By the shape of the head, the short antennae, and the fact that the gills pointed straight up and down -- sort of like the oar blades on a crew boat -- I knew that it was Ameletidae, but what species?
When I got home I looked at Steve Beaty's descriptions ("The Ephemeroptera of North Carolina," p. 1) in which five different species are keyed out for this part of the country -- cryptostimulus, lineatus, ludens, tarteri, and tertius. The A. tertius description caught my eye for one prominent reason: "distinctly marked small species with dorsal terga 3-6 with two large, ovalized submedian segments" (Beaty, p. 1) Bingo!
And another feature shows up in this photo as well -- "tarsi with both dark basal and apical bands." (Beaty)
But there were two other features that required some microscope work: 1) "ventrally pale except sterna 9 and 10 darkened (also sometimes a portion of 8)," and 2) "posterior spinules on abdominal terga 1 or 2-10."
Yes in both cases (though I realize it may be difficult in my photo to see the spinules except for those on segments 5 and 6, they were present on all of 2-10.)
Score again for the Rapidan River -- Ameletus tertius! Here's some more photos.
A. tertius is the fourth Ameletidae species I've found. The others,
Ameletus cryptostimulus,
Ameletus lineatus,
and in Montana, Ameletus subnotatus.
ReplyDeleteI have to agree with the above comment... you write very informative posts. Your blog has everything I like:
discovery of something new accurate and research-based information, and thorough and careful explanations.
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