Epeorus, Eaton, 1881, Eaton, 1881

Takayanagi, Tatsushi & Yoshizawa, Kazunori, 2025, Taxonomic review of Epeorus s. l. Eaton, 1881 (Ephemeroptera: Heptageniidae) in Sapporo City and adjacent areas, Hokkaido, Japan, Zootaxa 5594 (1), pp. 1-49 : 36-38

Key to mature nymphs in Sapporo City and adjacent areas

1 Gill I anteriorly enlarged ( Figs 16e , 17e , 24d , 25e ); gill VII with longitudinal fold ( Figs 17g , 25g ); pronotum slightly projecting laterally ( Figs 29b, d )................................................................................. 2

- Gill I not anteriorly enlarged ( Figs 6d , 7e , 11d , 21d , 22e ); gill VII without longitudinal fold ( Figs 7h , 22g ); pronotum roundly projecting laterally ( Figs 29a, c )......................................................................... 3

2 Gill I strongly enlarged and meet at beneath mesothorax ( Figs 15b, e , 16e , 17e ); posterior margin of abdominal terga with sharp denticles ( Figs 17j , 31c ).................................................................. E. (C.) curvatulus

- Gill I slightly enlarged and not meet at beneath mesothorax ( Figs 23b, e , 24d , 25e ); posterior margin of abdominal terga with blunt denticles ( Figs 25j , 31e )................................................................ E. (I.) aesculus

3 Gills with dark-violet spots ( Figs 6d , 11d ); gills II–VII with anal proximal projections ( Figs 6d , 11d ); posterior margin of abdominal terga with sharp denticles ( Figs 7k , 12g , 31a, b ).................................................... 4

- Gills without dark-violet spots ( Fig. 21d ); gills II–VII with anal ribs ( Fig. 21d ); posterior margin of abdominal terga with blunt denticles ( Figs 22j , 31d ).................................................................. E. (P.) nipponicus

4 Outer margin of inner incisor of the left mandible with sharp serration ( Fig. 7c )....................... E. (B.) latifolium

- Outer margin of inner incisor of the left mandible without sharp serration ( Figs 12c, f ).................. E. (B.) L-nigrum

Key to male imagines in Sapporo City and adjacent areas

1 Black markings on the base of veins of the forewing ( Figs 8e , 13e , 18e ).......................................... 2

- No markings on the base of veins of the forewing ( Fig. 26e )................................................... 3

2 Penis with titillators ( Figs 13f , 18f )....................................................................... 4

- Penis without titillators ( Fig. 8f )............................................................. E. (B.) latifolium

3 Forceps base without projection, penis laterally expanded with spines ( Fig. 26f )........................ E. (I.) aesculus

- Forceps base with projection, penis laterally expanded without spines (following Ma et al. 2021: p. 1149, figs 12c, 13c).......................................................................................... E. (P.) nipponicus

4 Posterior margin of styliger plate triangular edged ( Fig. 13f )....................................... E. (B.) L-nigrum

- Posterior margin of styliger plate rounded ( Fig. 18f )............................................ E. (C.) curvatulus

Figures

FIGURE 6a–d. Epeorus latifolium, mature nymph. a. Male head, dorsal view; b. Female head, dorsal view; c. Right middle leg, anterior face; d. Gills I–VII (from right to left), dorsal view. Scales: a–d 1mm.

FIGURE 7a–k. Epeorus latifolium, nymph. a. Labrum (left half in ventral view, right half in dorsal view); b. Incisors of right mandible (ventral view); c. Incisors of left mandible (ventral view); d. Setae on dorsal surface of femora; e. Gill I; f. Gill II; g. Gill IV; h. Gill VII; i. Sternum IX of male; j. Sternum IX of female; k. Posterior margin of tergum VII.

FIGURE 8a–g. Epeorus latifolium, male imago. a. Habitus, lateral view; b. Right hind leg, anterior face; c. Right middle leg, anterior face; d. Right fore leg, anterior face; e. Base of forewing, dorsal view; f. Genitalia, ventral view; g. Head and thorax, dorsal view. Scales: a 5mm, b–d 1mm.

FIGURE 11a–d. Epeorus L-nigrum, mature nymph. a. Male head, dorsal view; b. Female head, dorsal view; c. Right middle leg, anterior face; d. Gills I–VII (from right to left), dorsal view. Scales: a–d 1mm.

FIGURE 12a–g. Epeorus L-nigrum, nymph. a. Labrum (left half in ventral view, right half in dorsal view); b. Incisors of right mandible (ventral view); c. Incisors of left mandible (ventral view); d. Sternum IX of male; e. Sternum IX of female; f. New exoskeleton of incisors of left mandible, through the old one, ventral view; g. Posterior margin of tergum VII.

FIGURE 13a–g. Epeorus L-nigrum, male imago. a. Habitus, lateral view; b. Right hind leg, anterior face; c. Right middle leg, anterior face; d. Right fore leg, anterior face; e. Base of forewing, dorsal view; f. Genitalia, ventral view; g. Head and thorax, dorsal view. Scales: a 5mm, b–d 1mm.

FIGURE 15a–f. Epeorus curvatulus, mature nymph, habitus. a. Male, dorsal view; b. Male, ventral view; c. Male, lateral view; d. Female, dorsal view; e. Female, ventral view; f. Female, lateral view. Scales: a–f 2mm.

FIGURE 16a–e. Epeorus curvatulus, mature nymph. a. Male head, dorsal view; b. Frontal margin of male head; c. Female head, dorsal view; d. Right middle leg, anterior face; e. Gills I–VII (from right to left), dorsal view. Scales: a, c–e 1mm.

FIGURE 17a–j. Epeorus curvatulus, nymph. a. Labrum (left half in ventral view, right half in dorsal view); b. Incisors of right mandible (ventral view); c. Incisors of left mandible (ventral view); d. Setae on dorsal surface of femora; e. Gill I; f. Gill II; g. Gill VII; h. Sternum IX of male; i. Sternum IX of female; j. Posterior margin of tergum VII.

FIGURE 18a–f. Epeorus curvatulus, male imago. a. Habitus, lateral view; b. Right hind leg, anterior face; c. Right middle leg, anterior face; d. Right fore leg, anterior face; e. Base of forewing, dorsal view; f. Genitalia, ventral view. Scales: a 5 mm, b–d 1mm.

FIGURE 21a–d. Epeorus nipponicus, mature nymph. a. Male head, dorsal view; b. Female head, dorsal view; c. Right middle leg, anterior face; d. Gills I–VII (from right to left), dorsal view. Scales: a–d 1mm.

FIGURE 22a–j. Epeorus nipponicus, nymph. a. Labrum (left half in ventral view, right half in dorsal view); b. Incisors of right mandible (ventral view); c. Incisors of left mandible (ventral view); d. Setae on dorsal surface of femora; e. Gill I; f. Gill II; g. Gill VII; h. Sternum IX of male; i. Sternum IX of female; j. Posterior margin of tergum VII.

FIGURE 23a–f. Epeorus aesculus, mature nymph, habitus. a. Male, dorsal view; b. Male, ventral view; c. Male, lateral view; d. Female, dorsal view; e. Female, ventral view; f. Female, lateral view. Scales: a–f 2 mm.

FIGURE 24a–d. Epeorus aesculus, mature nymph. a. Male head, dorsal view; b. Female head, dorsal view; c. Right middle leg, anterior face; d. Gills I–VII (from right to left), dorsal view. Scales: a–d 1mm.

FIGURE 25a–j. Epeorus aesculus, nymph. a. Labrum (left half in ventral view right half in dorsal view); b. Incisors of right mandible (ventral view); c. Incisors of left mandible (ventral view); d. Setae on dorsal surface of femora; e. Gill I; f. Gill II; g. Gill VII; h. Sternum IX of male; i. Sternum IX of female; j. Posterior margin of abdominal tergum VII.

FIGURE 26a–f. Epeorus aesculus, male imago. a. Habitus, lateral view; b. Right hind leg, anterior face; c. Right middle leg, anterior face; d. Right fore leg, anterior face; e. Base of forewing, dorsal view; f. Genitalia, ventral view. Scales: a 5 mm, b–d 1mm.

FIGURE 29a–d. Lateral margin of pronotum, left. a. Epeorus latifolium, and E. L-nigrum; b. E. curvatulus; c. E. nipponicus; d. E. aesculus.

FIGURE 31a–e. SEM images of abdominal tergum VII (left half). a. Epeorus latifolium; b. E. L-nigrum; c. E. curvatulus; d. E. nipponicus; e. E. aesculus. Scales: a–e 50 µm.