Sunday, December 17, 2017
Pronggilled mayfly, Neoleptophlebia assimilis: identity confirmed
On August the 7th this year, I suggested that most of the Pronggilled mayflies I've found were Neoleptophlebia assimilis (then called Paraleptophlebia assimilis). That suggestion relied heavily on pigmentation. On morphology, I was missing one piece of evidence: I needed to see the mandibles to be sure they weren't N. swannanoa. I found a number of nymphs yesterday at the Doyles River (my upper site), and our identity can now be confirmed.
Let's work through our key (Larvae of the Souitheastern USA: Mayfly, Stonefly, and Caddisfly Species, pp. 140-141).
263 Gills 2-7 forked at one-fourth or more length from base; gill trachea with distinctly pigmented branches at least in unforked region.........264
263' Gills 2-7 forked near base, usually not more than one-sixth length from base; gill trachea without distinctly pigmented lateral branches, but often with very short and faint lateral branches.......267
Here's our nymph.
(You'll recall that the former nymphs are now genus Neoleptophlebia; the latter remain Paraleptophlebia.) We clearly move on to 264.
264 Mandibles relatively elongate, with about half length of angulate (left) mandible beyond angulate shelf.......Paraleptophlebia swannanoa
264' Mandibles not elongated as above, with less (usually much less) than half length of angulate mandible beyond angulate shelf........265
Here's what we have.
The portion above the angulate shelf is roughly 1/4 the length of the mandible. We move on to 265.
265 Posterolateral projections present on abdominal segments 8 and 9.......Paraleptophlebia( i.e. Neoleptophlebia) assimilis
[Note: projections on segment 8 are not well formed in young larvae.]
265' Posterolateral projections present on abdominal segment 9 only....266
Our larvae are very young. Still you can see the projections on 8.
Species ID confirmed! Neoleptophlebia assimilis.
Lots of Large winter stoneflies (Taeniopteryx maura/burksi) around yesterday;
Small winter stoneflies (Allocapnia pygmaea) as well.