The first fossil record of larval stages of parasitic isopods: cryptoniscus larvae preserved in Miocene amber

摘要

Fossil parasites represent rarities. In many cases, only trace fossils are preserved while body fossils are often lacking. We report here the first find of larval stages of parasitic isopods, identified as cryptoniscus larvae, from Chiapas Amber, Mexico (Lower Miocene). Different crustacean groups, including free-living isopods, have already been reported from the estuarine fauna presented in this type of amber. The seven specimens described here are interpreted as cryptoniscus larvae due to the following characters: 1) The general body organisation in combination with the appendage morphology. 2) A body length between 450 mu m and 695 mu m, which is known from larval stages of Bopyroidea and Cryptoniscoidea (Epicaridea). 3) The morphology of the uropods and the elongated and thin dactyli of the posterior thoracopods (pereiopods) are very similar to the condition in extant cryptoniscus larvae. Although parasitic behaviour can only rarely be directly identified in the fossil record, we can here clearly identify a specialised life stage, the cryptoniscus, which occurs only in a specific monophyletic group, of which all extant representatives are parasitic. These fossils not only represent rare cases of fossil parasites but also the first case of fossil peracarid larvae and the first body fossils of epicarid isopods.