Ontogenetic development captured in amber - the first record of aquatic representatives of Isopoda in Cretaceous amber from Myanmar

Abstract Two fossils from Burmese amber are the subject of this study. The specimens differ in size; yet, they appear to be conspecific because of the profound morphological similarity. The fossils are interpreted as representatives of Isopoda, more precisely of the group Cymothoida, due to the presence of a triangular basipod of the uropod. Cymothoida comprises parasitic forms of Isopoda as well as many other types of feeding-habits. The morphology in the studied fossils suggests that they are not representatives of any of the parasitic ingroups of Cymothoida. Since there are no other findings of Isopoda from the Cretaceous with the same morphological features, the fossils at hand are described as a new species - Electrolana madelineae sp. nov. The smaller specimen lacks well-developed walking appendages on trunk segment seven; it can thus be interpreted as a manca stage (immature) individual. The systematic affinity and the functional morphology of the herein described fossils, as well as three seed shrimps (Ostracoda) in close proximity to one of the specimens, and the presence of pyrite in the amber piece points towards an aquatic lifestyle and a preservation in moist conditions. In addition, we review the fossil record of immature forms of Isopoda.