Enrollment

At the Palaeozoic ecological system, trilobites took their place as predators and prey at the lower segments of the biotic pyramide. As desired choiced dishes at their contemporary predators menues (e.g. Nautiloidea, Crustacea, Ostracodermata asm.), the ability of enrollment was an effective method in withdrawing from unpopular consumption ;-)))

The images showing an enrolled trilobite of Order Phacopida (not yet fully ready prepped).

The ability of trilobites enrollment is based on the flexible articulation of the single thoracic segments. On principle the numb cephalon is locking with the just as numb pygidium (e.g. via vincular furrows). At some trilobites the thoracic pleurae are entering an overlapping or even meshing pattern. The limbs  getting folded and protected inside a closed protective capsule like the rest of the normally non- protected ventral surface.

Now one of the spinescence (genal- pleural- pygidial spines if present) functions is obvious from this. If the trilobite is enrolled in a tight closed capsule, the spines are prominent divaricated from capsules surface, and by this way inducing difficulties in swallowing or bite problems to hungry trilobites predators ;-)