The "mysterious" spiny crawler that I found at the Rapidan River on Sunday (6/10) turns out to be a genus of spiny I've not seen before -- and one that's unlisted in Peckarsky's Freshwater Macroinvertebrates -- Teloganopsis. I just had to work through the Ephemerellidae genera described in Beaty's "Ephemeroptera of North Carolina" in a more thorough way. And there, on p. 32, I found what I was after: a spiny crawler with Serratella-like caudal filaments (tails), but one that does not have submedian tubercles on the abdominal segments. Let's see what he says:
Genus Diagnosis: maxillary palpi absent (T. deficiens) or reduced (other species); claws with a stout preapical denticle; abdominal segment 1 without filamentous gill; lamellate gills present on abdominal terga 3-7 not operculate; sparse or no intersegmental setae on apical segments of caudal filaments; caudal filaments with whorls of spines at apex of each segment. (Beaty, p. 32)
on the species ID of T. deficiens, he adds:
T. deficiens -- nymphs 5-6 mm; maxillary palpi absent; no tubercles on head, pronotum or abdominal terga; claws with 8-10 denticles; often dark but color variable, sometimes with double pale dorsal stripes on segments 1-5.
He also notes, "Jacobus and McCafferty (2003) transferred Serratella deficiens to Teloganopsis of which T. deficiens is the only species in the eastern U.S."
I'll show you as many of those traits that I can: I could not get a good photo of the maxilla, but I assure you there is no "palp" present on either side.
1) I've already noted (entry of 6/10) the lack of tubercles on the abdominal segments. You can see that from the photo that follows, on which I've also noted the "lamellate gills" that are present on segments 3-6; the gill on 7 is mostly covered by the gill on 6.
2) This photo shows the "stout, preapical denticle" on a tarsal claw, and I can see 8 denticles on the claw.
3) On the whorls of spines on the caudal filaments and the lack of intersegmental setae -- here is a close-up of the tails:
Now, compare those tails with those of a genus Ephemerella spiny crawler, which lacks the whorls of spines and does have dense, intersegmental setae. (Click to enlarge so you can see the "feathery" ends of the tails.)
4) Finally, the nymph that I found was 5.5 mm in length, and it did have the "double pale dorsal stripes on segments 1-5" that are sometimes found on T. deficiens nymphs.
So, there you go. What spiny crawler has Serratella-like tails but lacks abdominal tubercles like Ephemerella dorothea? Teloganopsis deficiens. (Tolerance value for T. deficiens is 2.6.)
(For additional photos of T. deficiens, see Troutnut.com -- http://www.troutnut.com/specimen/594)