What nymphal morphology can tell us about parental investment – a group of cockroach hatchlings in Baltic Amber documented by a multi-method approach

Website of the journal Bulletin of Geosciences, published since 1925 by the Czech Geological Survey

Significance: Understanding the nature of the Cambrian radiation involves knowing not only the morphologies of adult animals but also their developmental pathways. However, fossil evidence of early larvae is rare. Here we describe a well-preserved 2-mm-long larva of the short-great-appendage arthropodLeanchoilia illecebrosafrom the early Cambrian Chengjiang biota. The exceptional 3D preservation has allowed our microcomputed tomography analyses to resolve a series of rudimentary limb Anlagen in the posterior portion of the larva—an arrangement resembling that in late-stage eucrustacean metanauplii.L. illecebrosais considered as an early representative of either chelicerates or of euarthropods as a whole. Therefore, this discovery provides fossil evidence that posthatching segment addition is a feature rooted in the ancestor of Euarthropoda.

Ticks can survive long periods without feeding but, when feeding, ingest large quantities of blood, resulting in a more than 100-fold increase of body volume. We study morphological adaptations to changes in opisthosoma volume during feeding in the castor bean tick, Ixodes ricinus. We aim to understand the functional morphological features that accommodate enormous changes in volume changes. Using light and electron microscopy, we compare the cuticle and epidermis of the alloscutum, the epithelium of the midgut diverticula, and the tracheae of adult female ticks when fasting, semi-engorged, and fully engorged. Our results add to an existing body of knowledge that the area of the epidermis increases by cellular differentiation, cellular hypertrophy, and changes in the shape of epithelial cells from pseudostratified to single layered prismatic in semi-engorged ticks, and to thin squamous epithelium in fully engorged ticks. We did not find evidence for cell proliferation. The midgut diverticula accommodate the volume increase by cellular hypertrophy and changes in cell shape. In fully engorged ticks, the epithelial cells of the midgut diverticula are stretched to an extremely thin, squamous epithelium. Changes in size and shape (and cell divisions) contribute to the accommodation of volume changes. Tracheae do not increase in size, but extend in length, thus following the volume changes of the opisthosoma in feeding ticks to secure oxygen supply to the internal organs. Changes of epithelial tissue configuration in the epidermis and the midgut diverticula are described as important components of the morphological response to feeding in ticks. We provide evidence for a previously unknown mechanism hosted in the endocuticle of the tracheae that allows the tracheae of castor bean ticks to expand when the body volume increases and the distance between the respiratory spiracle and the oxygen demanding tissue enlarges. This is the first report of expandable tracheae in arthropods.