Habits And Specialization

Except for short, hazardous dispersal of adults, embiids almost never leave the shelter of their self-created microenvironment, and most of the order's anatomical and behavioral characteristics foster very smooth, rapid, reverse movement in narrow galleries. Such specializations include the following:

1. A linear, short-legged, supple body with the head projected forward (Figs. 1 and 2).

FIGURE 1 Typical adult female: 'Aposthonia" n. sp. (family Oligotomidae) of Thailand; body length, 18.00 mm. Females of all species are apterous, and neotenic.
FIGURE 2 Typical adult male, wings in repose: Antipaluria caribbeana (family Clothodidae) of northern Venezuela; body length, 20.00 mm. Males of species inhabiting arid regions often are apterous, or subapterous.

2. Rapid reverse movement aided by great enlargement of depressor muscle of the hind tibiae.

3. Highly sensitive cerci serving as tactile guides during backward movement.

4. Complete apterism, and thereby elimination, of projecting structures in all females due to endocrinal arresting of development of adult anatomy (neoteny or pedomorphosis) at an early nymphal stage. Males of many species, especially in arid regions, also are apterous or subapterous.

5. Flexibility and forward folding of wings of adult males (Fig. 3)—an advantage in reverse movement as a means of reducing the barb effect against gallery walls and thus a slowing of reverse movement and thereby increased predation.

6. A compensating ability temporarily to stiffen wings for flight by increasing the blood pressure in the full length of the anterior radius (RA), the cubitus, and the anal vein (Fig. 4). This unique wing specialization must have early evolved in both sexes but has been supplanted in females by complete apterism through neoteny.

FIGURE 3 Forward wing-flip during defensive, reverse movement of a male: "Aposthonia" n. sp. (family Oligotomidae) of Thailand. In repose, wings are flexible; when extended for flight they are temporarily stiffened by blood pressure, particularly in the full length of the anterior radius vein.

FIGURE 3 Forward wing-flip during defensive, reverse movement of a male: "Aposthonia" n. sp. (family Oligotomidae) of Thailand. In repose, wings are flexible; when extended for flight they are temporarily stiffened by blood pressure, particularly in the full length of the anterior radius vein.

FIGURE 4 Typical embiid forewing: Pararhagadochir trinitatis (family Embiidae), Venezuela; wing length 10.0 mm. Most important are the blood sinus veins, especially the anterior radius (RBS, radial blood sinus); less important are the cubital blood sinus (CuBS) and the anal blood sinus (ABS). Hyaline stripes between veins also characterize embiid wings.

FIGURE 4 Typical embiid forewing: Pararhagadochir trinitatis (family Embiidae), Venezuela; wing length 10.0 mm. Most important are the blood sinus veins, especially the anterior radius (RBS, radial blood sinus); less important are the cubital blood sinus (CuBS) and the anal blood sinus (ABS). Hyaline stripes between veins also characterize embiid wings.

In spite of the great antiquity of the order, one that must predate the fragmentation of Pangaea, embiids constitute a single adaptive type of organism, one with a single "ground plan." As in earthworms, no great diversity of body form has occurred because of the physical uniformity of the galleries. As a result, it is difficult to sight-recognize various higher taxa. However, ages of evolutionary diversification are reflected in complex external genitalia of adult males, their head structures, and other characters useful in classification. Females and nymphs are difficult to identify without associated adult males. Adult females offer some anatomical characters in their paragenital sternites and hind tarsi; but size and coloration are most useful for species recognition of females.

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