Larval development of fossil polychelidan crustaceans, exemplified by the 150 million years old species Palaeopentacheles roettenbacheri

摘要

Here we present new ontogenetic data on a fossil polychelidan crustacean. Polychelida are benthic decapods known nowadays only from deep-sea habitats. Fossil representatives of Polychelida are known to inhabit shallower depths than the modern deep-sea inhabiting forms (= Polychelidae). Therefore, fossil polychelidans still retain certain ancestral traits such as compound eyes that are reduced in the modern forms. Such differences and the evolutionary changes are important to understand the evolutionary history of Polychelida. Furthermore, as Polychelida is the sister group to all other reptantian lobsters, Polychelida are crucial for a better understanding of the evolution of reptantian lobsters as a whole. In this study, we present an analysis of morphological development during the ontogeny of Palaeopentacheles roettenbacheri, a fossil representative of Polychelida from the 150 million years old (Upper Jurassic) Solnhofen Lithographic Limestones of southern Germany. The investigated specimens have exceptionally preserved tiniest details, which can be well visualised with autofluorescence microscopy. We discuss the morphological changes of the different developmental stages of P. roettenbacheri and how these changes point to a change in the life style: the shift from a pelagic mode of life to a benthic one. Furthermore, the potential evolutionary transformations of morphological traits are discussed by comparing morphological structures of modern polychelidan larvae to those of fossil ones. Based on these data, an evolutionary reconstruction is presented for the change of the larval development in Polychelida, ultimately leading to the highly specialised giant larvae known from modern forms.