Female Baetis subimago, copyright Jason Neuswanger.

Belongs within: Panephemeroptera.
Contains: Heptageniomorpha, Siphlonuroidea.

The Pisciformia are a group of mayflies characterised by nymphs with a fish-like body form and swimming mode. They include the infraorder Baetomorpha, members of which have fore wings with the tornal angle distad to CuP and nymphal maxillae with three dentisetae (Kluge & Sinitshenkova 2002). The Epeoromimidae are known from the Jurassic and Early Cretaceous from large-gilled nymphs only.

Everything you knew about mayflies is wrong
Mayfly nymph of the pisciform genus Baetis (Baetidae). Photo by Jan Benda.

Mayflies are one of the most basal, if not the most basal groups of winged insects alive today. The one thing that everyone knows about mayflies is that they only live for a day. This is reflected in their order name Ephemeroptera—”fleeting wing”. But like so many other things that “everyone knows”, this is complete twaddle. Mayflies do not live for a day. Indeed, by insect standards mayflies often have very long lives—many will live for an entire year, and some will live for as long as three years. The “fleeting” part of their lives is not their life as a whole, but only their time as adults.

Like dragonflies, mayflies spend the juvenile part of their life cycles as aquatic nymphs. They are easily distinguished from the aquatic nymphs of other insect orders by their three long caudal filaments and the leaf-like lateral gills that run down each side of their abdomens. Most mayfly nymphs are herbivorous or detritivorous, but a few are predatory. In contrast, adult mayflies have almost non-existent mouthparts, and do not feed—hence their “brief” lives. Mayflies are also unique in being the only living winged insects to undergo a moult after their wings develop. They first emerge from the water in a form known as the subimago, which soon moults into the final, fully mature imago. Mating usually happens in the imago stage, but there are some species that find themselves unable to wait that long, and begin mating as subimagoes (Grimaldi & Engel 2005).

Siphlonurus quebecensis (Siphlonuridae), another pisciform nymph. Photo from Troutnut.com.

The contrast between mayflies’ long juvenile lives and brief adult lives highlights a common prejudice to which almost all of us are prone— we tend to think of most animals in terms of their adult forms rather than their juvenile ones. There are a number of reasons for this. One is that we ourselves spend more of our life cycle (if we’re lucky) as adults than juveniles. Another is that the adults are usually larger and more visible than the often reclusive juveniles, so we’re more likely to notice them. Even working biologists may be prone to this trap—many animals can only be fully identified once they reach adulthood, which leads to the subconcious tendency to dismiss the unidentifiable juveniles as unimportant. But from an ecological perspective, it is the long-term juvenile mayflies that are far more significant than the brief adults. Adulthood in mayflies is simply a coda, a brief interlude to prepare for the next movement. Similarly, one could argue about how appropriate it is to characterise mayflies as flying insects when for so much of their lives they are not, with flight for them having no other purpose than to facilitate the reproductive process.

More Baetis nymphs. Photo by Surly Ghillie.

An influential classification of recent mayflies by McCafferty (1991) divided them into three suborders, Rectracheata, Setisura and Pisciforma, largely on the basis of their tracheal anatomy. Unfortunately, McCafferty did not explicitly refer to the characters on which he based the Pisciforma, other than noting that the name referred to the “minnow-like bodies and actions of the larvae”. McCafferty (1991) regarded the Pisciforma and Setisura as forming a clade to the exclusion of the Rectracheata. In contrast, Kluge (2004) used an alternative classification* that more or less united McCafferty’s Setisura and Rectracheata into a clade Bidentisetata, with two tooth-like setae on the maxilla (I say more or less because the families involved were not exactly the same), separate from the “Tridentisetata” (effectively McCafferty’s original Pisciforma) with three tooth-like setae. Kluge explicitly stated, however, that his Tridentisetata was a taxon of convenience united by plesiomorphies only and probably paraphyletic with regard to the Bidentisetata. Recent molecular analyses have confirmed that the “Pisciforma” are paraphyletic or polyphyletic. Ogden & Whiting (2005) found both Rectracheata and Setisura nested within Pisciforma, and suggested that the fish-like nymphal form was plesiomorphic for all living mayflies and lost on numerous subsequent occasions.

*Very alternative, in fact. Kluge (2004) introduced a new system of nomenclature that attempts to provide an alternative to the rank-based system. Without wanting to go into too many details (for a start, that would require me to actually follow what’s going on there, and frankly I haven’t got a clue), Kluge’s system involves a combination of a type genus plus a suffix indicating a taxon’s position in the taxonomic hierarchy. So Arthropoda, for instance, is referred to by Kluge as Araneus/fg7. Seriously.

A male baetid moulting into an imago. One of the easiest differences to spot between the submature subimagoes and the fully mature imagoes is that in the subimagoes the wings are generally opaque, while the imagoes have transparent wings. Photo stolen from Mick Hall.

There is one little detail that I have to mention before ending this post. One characteristic of the wings of living mayflies as a whole is a significant difference in size between the fore and hind wings, with the fore wings significantly larger. This is taken to its extreme in one of the pisciform families, the Baetidae, which are one of the few groups of insects in which the hindwings have been almost entirely lost, reduced to small pair of buds like those of flies.

Systematics of Pisciformia
    |  |  `--AenigmephemeraRJ93 [AenigmephemeridaeGE05]
    |  |       `--A. demouliniRJ93
    |  `--Epeoromimidae [Epeoromididae]GE05
    |       |--FoliomimusS02a
    |       `--Epeoromimus Tshernova 1969S02b
    |            |--E. cretaceous Sinitshenkova 1976S02b
    |            |--E. infractus Sinitshenkova 1989S02b
    |            |--E. kazlauskasiKS02
    |            `--E. umbratus Sinitshenkova 2002S02b
    `--Baetomorpha [Tridentiseta]KS02
         `--Baetoidea [Tetramerotarsata]KS02
              |  i. s.: Oniscigastridae [Oniscigastrini]PC91
              |           |--Oniscigaster distansPC66
              |           `--TasmanophlebiaPC91
              |                |--T. lacuscoeruleiPC91
              |                |--T. lacustrisPC91
              |                `--T. nigrescensPC91
              |         Ameletopsidae [Ameletopsinae, Ameletopsini]PC91
              |           |--Ameletopsis perscitusPC66
              |           |--Mirawara aaptaPC91
              |           |--ChaquihuaD68
              |           `--Balticophlebia Demoulin 1968D68
              |                `--*B. hennigi Demoulin 1968D68
              |--Siphlaenigma [Siphlaenigmatidae]KS02
              |    `--S. janaeRD77
                   |  i. s.: PalaeocloeonKS02
                   `--Baetidae [Baetinae, Turbanoculata]KS02
                        |--Centroptilum rotundum Takahashi 1929PC91, TYM08
                        |--Bungona narillaPC91
                        |--Callibaetis ferrugineusRD77, MG06
                        |    |--C. dipterumA99
                        |    |--C. emmavillensis Riek 1954F71
                        |    |--C. fluviatilePC91
                        |    |--C. inscriptumPC91
                        |    |--‘Cloe’ lituraF89
                        |    `--‘Cloe’ translucidaB89
                        |    |--B. amoenus Takahashi 1931 [=Boetis (l. c.) amoenus]TYM08
                        |    |--B. fluminumF89
                        |    |--B. giganteaRJ93
                        |    |--B. lutheriM86
                        |    |--B. magnus Takahashi 1931TYM08
                        |    |--B. rhodaniRD77
                        |    |--B. sororPC91
                        |    |--B. vardarensis Ikonomov 1962M86
                        |    `--B. venosaF89
                        |    |--C. bicoloratus Gattolliat 2001G01
                        |    |--C. freitagae Gattolliat 2001G01
                        |    |--C. portabilisG01
                        |    `--C. pseudoglodius Gattolliat 2001G01
                        |--Dabulamanzia gladiusG01
                        `--Baetodes Needham & Murphy 1924CA72
                             |--*B. serratus Needham & Murphy 1924CA72
                             |--B. adustus Cohen & Allen 1972CA72
                             |--B. andamagensis Mayo 1972M72
                             |--B. bellus Mayo 1972M72
                             |--B. caritus Cohen & Allen 1972CA72
                             |--B. chilloni Mayo 1972M72
                             |--B. deficiens Cohen & Allen 1972CA72
                             |--B. fortinensis Mayo 1972M72
                             |--B. fuscipes Cohen & Allen 1972CA72
                             |--B. inermis Cohen & Allen 1972CA72
                             |--B. itatiayanus Demoulin 1955CA72
                             |--B. levis Mayo 1968CA72
                             |--B. noventus Cohen & Allen 1972CA72
                             |--B. obesus Mayo 1972M72
                             |--B. pallidus Cohen & Allen 1972CA72
                             |--B. pictus Cohen & Allen 1972CA72
                             |--B. sancticatarinae Mayo 1972M72
                             |--B. solus Mayo 1972M72
                             |--B. spinae Mayo 1968CA72
                             |--B. spinifer Traver 1943 [=B. spiniferum]M72
                             |--B. traverae Mayo 1972M72
                             |--B. tritus Cohen & Allen 1972CA72
                             `--B. veracrusensis Mayo 1972M72

*Type species of generic name indicated


[A99] Ax, P. 1999. Das System der Metazoa II. Ein Lehrbuch der phylogenetischen Systematik. Gustav Fisher Verlag: Stuttgart (translated: 2000. Multicellular Animals: The phylogenetic system of the Metazoa vol. 2. Springer).

[CA72] Cohen, S. D., & R. K. Allen. 1972. New species of Baetodes from Mexico and Central America (Ephemeroptera: Baetidae). Pan-Pacific Entomologist 48 (2): 123–135.

[D68] Demoulin, G. 1968. Deuxième contribution à la connaissance des ephéméroptères de l’ambre oligocène de la Baltique. Deutsche Entomologische Zeitschrift (N. F.) 15 (1–3): 233–276.

[F71] Fletcher, H. O. 1971. Catalogue of type specimens of fossils in the Australian Museum, Sydney. Australian Museum Memoir 13: 1–167.

[F89] Fritze, A. 1889. Ueber den Darmkanal der Ephemeriden. Berichte der Naturforschenden Gesellschaft zu Freiburg I. B. 4: 59–82, pls 2–3.

[G01] Gattolliat, J.-L. 2001. The genus Cloeodes (Ephemeroptera: Baetidae) in Madagascar. Revue Suisse de Zoologie 108 (2): 387–402.

[GE05] Grimaldi, D., & M. S. Engel. 2005. Evolution of the Insects. Cambridge University Press: New York.

Kluge, N. 2004. The Phylogenetic System of Ephemeroptera. Springer.

[KS02] Kluge, N. Yu., & N. D. Sinitshenkova. 2002. Order Ephemerida Latreille, 1810. The true mayflies (=Ephemeroptera Hyatt et Arms, 1891 (s. l.); =Euephemeroptera Kluge, 2000. In: Rasnitsyn, A. P., & D. L. J. Quicke (eds) History of Insects pp. 89–97. Kluwer Academic Publishers: Dordrecht.

[MG06] Mallatt, J., & G. Giribet. 2006. Further use of nearly complete 28S and 18S rRNA genes to classify Ecdysozoa: 37 more arthropods and a kinorhynch. Molecular Phylogenetics and Evolution 40: 772–794.

[M86] Marten, M. 1986. Drei für Deutschland neue und weitere, selten gefundene Eintagsfliegen aus der Fulda (Insecta, Ephemeroptera). Spixiana 9 (2): 169–173.

[M72] Mayo, V. K. 1972. New species of the genus Baetodes (Ephemeroptera: Baetidae). Pan-Pacific Entomologist 48 (4): 226–241.

McCafferty, W. P. 1991. Toward a phylogenetic classification of the Ephemeroptera (Insecta): a commentary on systematics. Annals of the Entomological Society of America 84 (4): 343–360.

Ogden, T. H., & M. F. Whiting. 2005. Phylogeny of Ephemeroptera (mayflies) based on molecular evidence. Molecular Phylogenetics and Evolution 37: 625–643.

[PC66] Pendergrast, J. G., & D. R. Cowley. 1966. An Introduction to New Zealand Freshwater Insects. Collins: Auckland.

[PC91] Peters, W. L., & I. C. Campbell. 1991. Ephemeroptera (mayflies). In: CSIRO. The Insects of Australia: A textbook for students and research workers 2nd ed. vol. 1 pp. 279–293. Melbourne University Press: Carlton (Victoria).

[RD77] Richards, O. W., & R. G. Davies. 1977. Imms’ General Textbook of Entomology 10th ed. vol. 2. Classification and Biology. Chapman and Hall: London.

[RJ93] Ross, A. J., & E. A. Jarzembowski. 1993. Arthropoda (Hexapoda; Insecta). In: Benton, M. J. (ed.) The Fossil Record 2 pp. 363–426. Chapman & Hall: London.

[S02a] Sinitshenkova, N. D. 2002a. Ecological history of the aquatic insects. In: Rasnitsyn, A. P., & D. L. J. Quicke (eds) History of Insects pp. 388–426. Kluwer Academic Publishers: Dordrecht.

[S02b] Sinitshenkova, N. D. 2002b. New late Mesozoic mayflies from the Shar-Teeg locality, Mongolia (Insecta, Ephemerida=Ephemeroptera). Paleontologicheskii Zhurnal 2002 (3): 43–48 (translated: Paleontological Journal 36 (3): 270–276).

[TYM08] Tennent, W. J., M. Yasuda & K. Morimoto. 2008. Lansania Journal of arachnology and zoology—a rare and obscure Japanese natural history journal. Archives of Natural History 35 (2): 252–280.

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