Mayfly Species Acentrella parvula (Miniature Blue-Winged Olives)

Head: An interrupted brown submedian line over vertex and frons, remainder mostly pale; antennae relatively long extending back to tip of wing pads.

Thorax: Dorsum mostly brownish with restricted pale areas; wing-pads with longitudinal veins traced in brown; legs pale, banded with dark, a band basally on femur, another, sometimes broken, about the middle and an incomplete band distally; tibia with dark band distally and tarsus with dark band proximally; tarsal claws pectinate.

Abdomen: Very strikingly marked dorsum as shown in fig: 19. In a typical segment there is a row of pale areas across the anterior border of the segment, one median and a pair of submedian on each side; the lateral region of the segment is pale; a row of submedian dark dots down the middle of the dorsum in front of which in segments 8 and 9 are dark strokes converging anteriorly; venter with paramedial row of indistinct dark dots about the middle of each segment and in front of each dot a dark stroke converging towards the anterior border: tracheae distinct laterally; the caudal filaments are rather unique as far as I know in this genus in being alternately light and dark banded; the median filament is short being considerably less in length than the width of one of the lateral filaments at the base; the gills also are distinctive having distally an irregular pigmented area. Nymphs readily distinguished from females of P. dubium and P. virile by the maculate gills, and the alternately light and dark banded caudal filaments.

Abdominal tergites 2-6 of male imago dull hyaline whitish, suffused with a slight smoky or pale amber; large ruddy lateral patches on each side.

Turbinate eyes deep reddish in dried specimen and more oval than in P. dubium (now a synonym of Plauditus dubius) Thorax blackish brown. Fore femur smoky, tinged slightly with amber; tibia and tarsus smoky white. Femora of middle and hind legs pale, very faintly tinged with amber, each with a ruddy dash anteriorly on the lower edge and a distinct ruddy lateral spot near the apex and well beyond the middle of the joint. Tibiae and tarsi whitish. Wings hyaline, tinged slightly with blackish brown at the extreme base; venation pale. A very few cross veins in the stigmatic area, no granulations between them. Abdominal tergites 2-6 dull hyaline whitish, suffused with a slight smoky or amber tinge. Traces of a fine ruddy mid-dorsal geminate line. Laterally on each tergite is a large diffuse ruddy or claret-colored patch; that on tergite 4 is less distinct, may even be obsolescent. Tergites 7-10 light chocolate brown; sternites opaque whitish tinged with brown, this being deepest on the lateral area of sternite 9. Basal sternites hyaline, faintly suffused with amber or smoky. Spiracular area marked with black. Forceps pale; basal joint suffused with light sepia brown; distal joint short and stubby, scarcely longer than broad (see fig. 168); in P. dubium, this joint is much longer. Tails whitish.

This species is smaller than any other thus far described, except P. futile (now a synonym of Apobaetis futilis), from which it is readily distinguished by the ruddy lateral abdominal patches and the dull hyaline of the basal abdominal segments. The ruddy lateral markings are less extensive than in P. rubrolaterale (now a synonym of Iswaeon rubrolaterale), which also possesses dark mid-ventral dots on the abdomen.