Tuesday, January 17, 2012

More on the Flatheaded Mayfly, Maccaffertium meririvulanum

In the small stream that I went to on Saturday morning (1/14), in which I found those beautiful Lepidostomatid caddisfly larvae, I also found two fairly big flatheaded mayflies that I brought home for closer inspection.  The one in the picture above turned out to be Maccaffertium meririvulanum, a species I had found in another small stream in Sugar Hollow on 12/11 and identified in a blog entry on 12/13.

M. meririvulanum was first identified as a new flatheaded species in 1978 in an article by Frank Louis Carle and Philip A. Lewis in the Annals of the Entomological Society of America (71:3, pp. 285-288) -- "A New Species of Stenonema (Ephemeroptera: Heptageniidae) from Eastern North America."  (Remember that the label Maccaffertium has since replaced Stenonema in entomological writings.)   I have my good friend who lives in Sugar Hollow to thank for referring me to this publication.

There are a number of points in this article that are worth passing on.

1) First, Carle and Lewis succinctly describe the key features for species identification right from the start.  "Nymphs are characterized by "V"-shaped pale areas on abdominal terga 7-9, posterolateral spines on abdominal segments 6 or 7-9, and an unmarked abdominal venter" (p. 285).  While the dorsal "V's" are fairly clear in the photo above, they are clearer still in this microscope shot.

And when the nymph is flipped on its back, we can easily see the "unmarked abdominal venter" and the posterolateral spines.

An additional trait that is added in Beaty ("The Ephemeroptera of North Carolina," p. 19) is that there are "no hairs and 7-10 spine-like setae on the maxillary crown."  I count 9 spines on this one.

Carle and Lewis also comment later on in the article that "the extremely long caudal filaments will apparently separate adult Stenonema meririvulanum from all other Stenonema."  I don't know that this has been picked up in later studies.  But, for the record, this nymph was 12mm long, and the caudal filaments (tails) were 20mm.

2) Secondly, on habitat and distribution, Carle and Lewis have three comments to make.   1) "The known distribution of S. meririvulanum extends along the Appalachian Mountains from Pennsylvania to Georgia."  2) Stenonema meririvulanum is an uncommon species that inhabits the riffles and pools of very small spring-fed streams, and has been found in larger streams only near the mouth of small tributaries."  And 3, "The species has been collected from small pristine streams in the Appalachian Mountains." (I've put words in "Bold" that I think deserve our attention.)   The two streams in which I've found this flatheaded species are in the Blue Ridge, they are both "very small spring-fed streams" that tumble down from the tops of the mountains through rocky ravines in totally forested land (no human contact), and, they are indeed "pristine."

3) Finally, our authors add "Species of Heptageniidae collected with S. meririvulanum at other localities are S. allegheniense, S. pudicum, Stenacron carolina, Epeorus pleuralis, and Heptagenia hebe McDunnough."  On Saturday, in addition to this M. meririvulanum nymph I found several small Epeorus pleuralis flatheads (there will be lots of them here in the next couple of months), and I found this fairly large M. pudicum.

How about that!  I feel privileged to find "uncommon species" and to work in "pristine streams" that are not far from home.  (The tolerance value of M. meririvulanum is 0.5; that of M. pudicum is 2.1.   Carle and Lewis give the etymology of meririvulanum as "belonging to small pristine brooks.")

(Below: the M. Meririvulanum found in Sugar Hollow on 12/11.)

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