Another variation of defensive morphotype is exhibited by the wingless half-ellipsoids, those cockroaches that are rounded on top and flat on the bottom, like a watermelon cut on its long axis. Species of this shape in several genera of Perisphaeriinae (Perisphaeria, Perisphaerus, and Pseudoglomeris) are able to roll themselves into a ball, that is, conglobulate, when alarmed (Fig. 1.12) (Shelford, 1912a; Roth, 1981b). They are usually rather small, black species with a tough cuticle. When enrolled, the posterior abdomen fits tightly against the edge of the pronotum. All sense organs are covered; there are no gaps for an enemy to enter nor external projections for them to grab (Fig. 1.11B). In some species, the female encloses young nymphs that are attached to her venter when she rolls up (Chapter 8). Not only are small predators like ants thwarted, but the rounded form is very resistant to pressure and requires considerable force to crush (Lawrence, 1953). In other taxa exhibiting this behavior (e.g., isopods, myriapods), the rolled posture is maintained during long periods of quiescence, so that the animal is protected from desiccation as well as enemies (Lawrence,
1953); it is unknown whether that is the case in these cockroaches.
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