British Insects: the Genera of Ephemeroptera

DELTA Home

L. Watson and M. J. Dallwitz

Character List

#1. <Synonyms:>/

Imago.

#2. <Sex of imago>/

1. male/

2. female/

Sub-imagines other than those of Caenidae are distinguishable from imagines by their fringed, relatively dull wings, and those of males have incompletely developed genitalia. Both imagines and sub-imagines of the Caenidae are supposed to key out together via the characters offered.

#3. The compound eyes <of imagines, separation>/

1. contiguous/

2. widely separated/

#4. The compound eyes <of imagines, two-lobed or not>/

1. distinctly two-lobed <the larger, upper lobe usually with larger facets than those of the lower, in which they are usually darker>/

2. rounded <not lobed, though sometimes two-coloured>/

#5. The upper lobe <of the compound eyes of imagines, whether turbanate>/

1. turbanate <turban-shaped>/

2. rounded/

#6. Second antennal segment <of imagines and sub-imagines, relative length>/

1. three times as long as the first/

2. no more than twice as long as the first/

#7. Wings <whether fringed>/

1. fringed in the imago <Caenidae only>/

2. fringed only in sub-imagines <implicit>/

#8. Wings <of imagines and sub-imagines, spotted or unspotted>/

1. more or less spotted with brown or blackish/

2. unspotted <dubiously implicit>/

#9. Fore-wings <of imagines and sub-imagines, whether veins M1 and Cu1 are strongly divergent>/

1. with veins M1 and Cu1 strongly strongly diverging basally/

2. with veins M1 and Cu1 sub-parallel basally <implicit>/

#10. Fore-wings <of imagines and sub-imagines, whether veins R4 and R5 detached>/

1. with R5 detached basally from R4/

2. with R5 and R4 joined basally <implicit>/

#11. The marginal fore-wing veinlets <of imagines and sub-imagines, whether single or paired between the main longitudinal veins>/

1. single/

2. paired/

#12. Hind-wings <of imagines, present or absent>/

1. present <though sometimes very reduced>/

2. absent <even as vestiges>/

#13. The hind-wings of the female imagines <length relative to fore-wings: data recorded only for two-tailed females!>/

1. no more than one fifth the length of the fore-wings/

2. more than one fifth the length of the fore-wings/

#14. The hind-wing costa <of imagines and sub-imagines, smoothly curved or with a projection>/

1. smoothly curved/

2. with a conspicuous projection/

#15. The fore-legs <of imagines, insertion close or distant>/

1. inserted relatively close together under the thorax/

2. widely separated under the thorax/

#16. Hind tarsi <of imagines and sub-imagines, length relative to the tibia>/

1. about one-and-a-half times the length of the tibia <Siphlonurus>/

2. slightly shorter than the tibia <Ameletus>/

#17. Hind tarsi <of imagines and sub-imagines, number of moveable segments>/

1. with 5 moveable segments/

2. with 4 moveable segments <the fifth, if present, fused to the tibia>/

3. with 2–3 moveable segments/

This character is emphasized in the otherwise rather different keys presented by Kimmins (1954) and Imms (1957), probably because it featured in Ulmer’s (1933) classification, but the details need checking. While Kimmins states that “in the Baetidae, the hind tarsus has the appearance of only 3 free segments, the two basal ones being fused to the tibia”, his drawing of the hind tarsus of Cloeon dipteron shows four (as also do Harker’s diagrams of both Cloeon and Procloeon).

Sub-imagines other than those of Caenidae are distinguishable from imagines by their fringed, relatively dull wings, and those of males have incompletely developed genitalia. Both imagines and sub-imagines of the Caenidae are supposed to key out together via the characters offered.

#18. The first segment of the hind tarsus <of imagines, length relative to the second segment>/

1. about twice as long as the second/

2. about three times as long as the second/

#19. The hind tarsal claws <of imagines, whether both pointed or one blunt and one pointed>/

1. both pointed/

2. unalike, being one pointed and one blunt/

#20. The abdomen <of imagines, number of tails>/

1. with two tails/

2. with three tails/

#21. Male claspers <crossed or separate>/

1. crossed/

2. separate/

#22. The lobes of the penis <broad or narrow>/

1. very broad-tipped, and closely approximated/

2. narrow, rod-shaped, and widely separated/

Nymph.

#23. The lobes of the penis <appendages/spurs>/

1. each with one recurved appendage <spur>/

2. each with two recurved appendages <spurs>/

3. without recurved appendages/

#24. The outer tails <of nymphs, distribution of hairs>/

1. hairy <bearing long hairs> on the inner side only/

2. hairy on both sides/

#25. Gills <of nymphs, position on abdomen>/

1. mostly at the sides of the abdomen/

2. mostly lying on the upper surface of the abdomen/

#26. Gills <of nymphs, fringing>/

1. all densely fringed with filaments on both sides/

2. not fringed with filaments on both sides/

Classification.

#27. Gills <of nymphs, whether consisting of a plate with a tuft of filaments>/

1. mostly consisting of a plate bearing a tuft of filaments/

2. never comprising a plate bearing a tuft of filaments/

#28. Superfamily/

1. Ephemeroidea/

2. Baetoidea/

3. Heptagenioidea/

British representation.

#29. Family/

1. Baetidae/

2. Caenidae/

3. Ephemeridae/

4. Ephemerellidae/

5. Heptageniidae/

6. Leptophlebiidae/

7. Potamanthidae/

8. Siphlonuridae/

#30. <Number of species in Britain>/

species/

Miscellaneous.

#31. <British species list, with binomials and anglers’ colloquial names>/


To view illustrations with legends giving names in current use, go to the interactive key. This also offers full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, and distributions of character states within any set of taxa, as well as source references and other relevant material.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2003 onwards. British insects: the genera of Ephemeroptera. Version: 29th December 2011. http://delta-intkey.com’.

Contents