Family Euphaeidae

The larvae of 6 of the 8 genera and approximately one third of the total of 79 species are known but not necessarily individually described. The family is exclusively Oriental with the exception of the monotypic genus Epallage, ranges from south-east Europe to Kashmir, politically within Indian borders, but placed by Holt et al. (2013) in the Saharo-Arabian realm. Within the Oriental region the family is conspicuously absent from Sulawesi and Wetar and Timor in Indonesia.

Euphaeid larvae are unmistakable by virtue of the series of long paired fleshy gills on the venter of abdominal S2–8 (Fig. 1). These are present even on very young larvae and begin to develop early in embryogenesis (Suzuki et al. 2020, Ng 2024d). The habitus (examples Figs 57–60) is overall flattened, reminiscent of Plecoptera, with broad flattened femora adapted to clinging to the underside of stones and large boulders where they are generally to be found in swiftly flowing clear water and rapids. All have saccoid caudal gills (Figs 67–70), the form of which is of some diagnostic value, but these may be lost and/or shrivelled in exuviae. Euphaeid larvae were first described by Hagen (1880) with reference to Euphaea splendens Hagen from Sri Lanka and tentatively? Anisopleura comes Hagen and? Euphaea dispar Rambur, however he incorrectly stated that the abdominal gills were born on S1–8. This was corrected by J.W Folsom, published in Packard (1898), who also noted the tracheation of the abdominal gills and depicted a convincing habitus and detail of a single gill of E. splendens . A respiratory function for the abdominal gills was deduced by Hagen (1880), Packard (1898) and Tillyard (1917), which was later queried by several authors following Fraser’s (1933) assertion that they were grasping organs, before the respiratory hypothesis was settled conclusively by Norling (1982). Intrageneric variation, inadequate species sampling and poor artwork in some available descriptions sometimes makes a universal distinction between Anisopleura, Bayadera and Euphaea tentative, although certain species within these genera are distinctive. Important diagnostic characters include the shape of the postocular lobes of the head, relative length of antennae, distribution of tubercles and claviform setae on the head, development of male genital apophyses, armature of outer mandibles (Fig. 62a), subocular spines (Fig. 62b) and presence of supracoxal and coxal spurs (Keetapithchayakul et al. 2020, Yang & Orr 2024, Keetapithchayakul et al. 2024, Orr & Hämäläinen 2024).

Larva unknown: Cyclophaea (1 sp.), Schmidtiphaea (1 sp.)

Key to genera

1 Head massive, nearly twice width of pronotum; genae swollen and projecting well beyond eyes in dorsal view bearing numerous short heavy spines; strong spines present on bulbous postocular lobe (Figs 57, 61).......................... Dysphaea [widespread west of Wallace’s line]

1’ Head narrower in relation to pronotum, genae not swollen, no strong spines on postocular lobe which is not bulbous....... 2

2 (1’) Genae with 6–7 long subocular spines (greater than one third width of eye viewed ventrally); antennae with 12–15 antennomeres including pedicel and scape; outer face of mandibles with 2 or 3 rows of strong spines [4 ventral, 5 dorsal, 0–4 central] (Fig. 62)....................................................................................... Heterophaea [endemic to north-eastern Luzon, Philippines]

2’ Genae with 5 or fewer long subocular spines; antennae with 7, rarely 8 antennomeres; outer margin of mandible with only one row of spines, or just one or two long spines............................................................... 3

3 (2’) Antennae distinctly shorter than head from occipital margin to base of labrum; postocular lobes shallow, weakly rounded (Fig. 63); labrum, frons and vertex with smattering of variably developed tubercles, low or raised and finger-like; caudal gills tapered to long, fine filament (Fig. 67)................................................................. Anisopleura

3’ Antennae at least as long as or longer than head from occipital margin to base of labrum postocular lobes deep and strongly rounded at corners, sometimes appearing square by virtue of tuft of setae (Figs 64, 65); tubercles on head lacking or very sparse; caudal gills terminating in long filament or a short blunt cone, sometimes constricted basally......................... 4

4 (3’) Caudal gills terminating in a short blunt cone (Figs 58, 68) occasionally basally constricted; antennae clearly longer than head from occipital margin to base of labrum (Fig. 64); outer margin of outer process of labial palp wavy (Fig. 66); male gonapophyses down-curved and sausage shaped, overlapping S10 (Fig. 71)................................ B a yadera

4’ Tip of caudal gills with long filament usually arising abruptly from sac of gill (Figs 59, 69) or sac elongate with a short blunt filament ( E. superba Fig. 70); antennae about equal to head from occipital margin to base of labrum or slightly longer (Fig. 65); outer margin of outer process of labial palp smooth; male gonapophyses small and triangular or vestigial, not overlapping S10 (Fig. 72)...................................................................................... Euphaea