Agrenia

Genus Agrenia Börner

The genus is well defined and was reviewed by Fjellberg (1986) and Fjellberg & Bernard (2009). In the course of our study of neustonic fauna two species were collected. One of them, supposedly a new species, belonged to ' bidenticulata ' group and differed from the widely distributed arctic species A. bidenticulata by longer claws. To clarify the independence of the Buryatian form we have studied other populations of A. bidenticulata from Russian Arctic and Siberian mountains.

Key to the species of Agrenia

1. Mucro withlateral seta absent ....................................................................................................................................... 2

- Mucro with lateral seta present..................................................................................................................................... 9

2. Ventral tube in adults with six or fewer anterior setae on each side............................................................................. 3

- Ventral tube in adults with ten or more anterior setae on each side.............................................................................. 7

3. Subapical seta on dens reaching well beyond tip of mucro (Fig. 1 A) .......................................................................... 5

- Subapical seta on dens short, not reaching beyond tip of mucro (Figs. 1 E–G)........................................................... 4

4. Claws very long and slender, claw index 3.0 or more; body setae thin, sparse, uniform; outer dorsal lamella of mucro not prominent (Fig. 1 F) .................................................................................................. falcula n. sp. (Appalachians)

- Claws shorter, claw index less than 3.0; body setae strong, on head and thorax with mixed short and long setae; outer dorsal lamella of mucro high and distinct (Fig. 1 G)............................................. tarashchukae n. sp. (Appalachians)

5. Colour deep greenish black; ventral tube without anterior setae .................................................. atroviridis (Rockies)

- Colour olive; ventral tube with or without anterior setae ........................................................................................... 6

6. Antennae no more than 1.8 times the length of head diagonal; anterior setae on ventral tube usually absent, occa- sionally 1–2 on each side; claw index in summer specimens 2.1–2.5, in winter specimens 1.2–1.3 ............................. .......................................................................................................................................................... riparia (Holarctic)

- Antennae in adults more than 1.8 times the length of head diagonal, in large males up to 2.7 times as long; ventral tube usually with 4–5 anterior setae on each side, rarely absent; claw index 2.8–4.5 (summer) and 2.0–2.7 (winter)..

........................................................................................................................................ parkeri n. sp. (Appalachians) 7. Mucro elongate, apical tooth larger than subapical tooth (Fig. 6 B); maxilla with short, unmodified lamellae (Fig. 1 M) ............................................................................................................................................................................... 8 - Mucro short and compact, apical tooth not larger than subapical tooth (Fig. 1 A); maxilla with long, modified lamellae (Fig. 1 L) ............................................................................................................................. extrema n. sp. (Rockies)

8. Claws long and slender, claw index 2.8 or more; head markedly prognathous; abdominal setae of normal density ... ........................................................................................................................................... agilis (Pacific Coast Range)

- Claws shorter, shape normal; claw index 2.3 or less; head shape normal, not markedly prognathous; abdominal setae dense, Isotomurus -like ..................................................................................................................... cyanura (Rockies)

9. Ventral tube with fewer than 20 anterior setae on each side; setae along anterior edge of frontoclypeus normal, not differentiated into a "moustache" ............................................................................................................................... 10

- Ventral tube in adults with more than 30 anterior setae on each side; frontoclypeal field with a distinct "moustache" ................................................................................................................................................................ pilosa (Japan)

10. Mucro short and compact, with narrow ventral lamella .......................................................................................... 11

- Mucro elongate, with broad ventral lamella (as in Fig. 1 E–F) ............................................ lamellosa (Appalachians)

11. Body usually with some segments, or parts of segments, darker than rest; reproductive specimens unmodified ........ ............................................................................................................................................... bidenticulata (Holarctic)

- Body colour uniform, without distinctly darker sections; large reproductive specimens with modified setae on tip of abdomen .................................................................................................................................... polymorpha (Rockies)