Sternite organization during enrollment in terrestrial isopods and glomerid millipedes. (a–c) Micro-CT scan of terrestrial isopod MCZ:IZ:90105. (a) Tomographic model of 90% enrolled specimen. (b) Micro-CT scan of full specimen with three segmented sternites (blue highlight). (c) Micro-CT segmented sternites from three trunk segments. (d–f) Micro-CT scan of glomerid millipede MCZ:IZ:165554-2. (d) Tomographic model of completely enrolled specimen. (e) Reconstruction of full specimen with three segmented sternites (blue highlight) and pleurites (yellow highlight). (f) Micro-CT segmented sternites from three trunk segments. ai, anterior imbrication; ant, antenna; col, collum; ple, pleurite; ps, posterior shield; st, sternites; te, telson; ter, tergite. Credit: Proceedings of the Royal Society B: Biological Sciences (2023). DOI: 10.1098/rspb.2023.2212
Phys.org has a story that shed light how trilobites evolved the ability to enroll their bodies for protection against predators. A team of researchers from Harvard examined a museum specimen that had preserved sternites, where were plates that lined the stomach of trilobites. Using micro-CT scans, the researchers could see how the plates slid past one another a then lock into place. The locking mechanism provided a tight and save rollup. The whole procedure is similar to modern day animals, such as armadillos and pill bugs, that can enroll their bodies. Details can be found in the paper "Convergent evolution of ventral adaptations for enrolment in trilobites and extant euarthropods" published in the journal Proceedings of the Royal Society B.
Prior research has shown that many creatures have independently evolved the ability to curl themselves into a ball as a means of protection from predators—most such creatures, such as armadillos and pill bugs, have a protective shell as the outside of the ball. Prior research has also shown that trilobites (a long extinct type of tiny marine arthropod) also curled themselves into balls to avoid being eaten, but to date, very little evidence has been found regarding their internal organs due to their soft nature—non-biomineralized tissue was rarely preserved.
In this new effort, the research team found a way around this problem when one of the team members discovered an enrolled sample with preserved sternites—plates that line the stomach of trilobites—in the museum's collection.
