Mayfly Species Caenis eglinensis (Angler's Curses)

Source: A new species of Caenis (Ephemeroptera: Caenidae) from Florida, USA

Diagnosis. Caenis eglinensis can be distinguished from other North American species of Caenis by the following combinations of characters.

In the nymph: (1) pronotum strongly divergent anteriorly (Fig. 2); (2) posteromedian projection of abdominal tergum II moderately long, and projected almost vertically with apex pointed in both lateral and dorsal views (Fig. 5); (3) femora with a prominent dark brown to black subapical band almost encircling entire segment (Fig. 3); (4) abdominal terga IX and X each with triad of black dots; (4) posterior margin of sternum IX rounded (Fig. 6); and (5) caudal filaments uniformly pale.

In the adults: (1) wing vein ICuA 1 forked with CuA 1 basad of ICuA 1 - CuP crossvein; (2) forefemur smoky brown, middle and hind femora pale with broad black subapical band almost encircling entire segment; (3) genitalia with penes truncate apically and forceps tan, relatively short, straight, and densely covered with overlapping microspines (Figs. 8, 9); (4) abdominal terga IX and X each with triad of black dots and (5) abdominal color pattern similar to Fig. 72 in Provonsha (1990) with lighter pigmentation.

Based on the definitions of the two species groups of North American Caenis, the diminuta group and hilaris group (Provonsha, 1990), Caenis eglinensis belongs to the diminuta group which includes Caenis amica, Caenis candida, Caenis diminuta, Caenis latipennis, Caenis punctata and Caenis youngi. Caenis eglinensis can be distinguished from the other species of the diminuta group by the following combinations of characters.

In the nymph: (1) pronotum strongly divergent anteriorly (Fig. 2); (2) posteromedian projection of abdominal tergum II moderately long and projected almost vertically (Fig. 5) with apex pointed; (3) posterior margin of abdominal sternum IX rounded; and (4) abdominal color pattern similar to Fig. 1. The nymphs of both Caenis eglinensis and Caenis youngi have a strongly divergent pronotum and long posteromedian projection of abdominal tergum II, but in the nymphs of Caenis eglinensis, the posteromedian projection of abdominal tergum II is apically pointed, while broadly rounded in Caenis youngi. The anteriorly divergent pronotum and long, upright projection of abdominal tergum II distinguish Caenis eglinensis from both Caenis diminuta and Caenis punctata.

The adults of Caenis eglinensis, Caenis diminuta, and Caenis punctata are all similar in overall color pattern, though the pigmentation of Caenis eglinensis adults is generally lighter. The genital forceps of Caenis eglinensis and Caenis punctata are relatively short, straight, and densely covered with overlapping microspines (Fig. 9), distinguishing them from Caenis diminuta, whose forceps are comparatively longer, incurved, and sparsely covered with microspines (Fig. 10). In the adults: (1) femora with broad black subapical band almost encircling entire segment; (2) abdominal color pattern similar to Caenis diminuta but lighter; and (3) genitalia with penes truncate apically and forceps relatively short and densely covered with overlapping microspines (Figs. 8, 9). Adults of Caenis eglinensis and Caenis punctata can be distinguished by the color of the antennae and pigmentation of the legs. The antennal scape and pedicel of Caenis eglinensis are shaded grayish black, while in Caenis punctata the scape and pedicel are entirely pale. The black pigmentation of the middle and hind legs of Caenis eglinensis is restricted to the black subapical band of the femora, while Caenis punctata have black speckling along the femora and on the tibiae, in addition to the black subapical band. The absence of a fleshy finger-like projection on abdominal tergum II of Caenis eglinensis which is well developed in Caenis youngi easily distinguishes the adults of the two species.