Moulting and development in a freshwater prawn from the Cretaceous of Morocco

The lowermost Upper Cretaceous (Cenomanian) Kem Kem Group of Morocco is renowned for its rich fossil record, particularly that of macrofossils from freshwater facies, which includes insects, fish, and the penaeid prawn Cretapenaeus berberus Garassino, Pasini & Dutheil, 2006 (Dendrobranchiata: Penaeidae). Here, we provide information on growth in this extinct species, based on a sample of 65 specimens. These provide valuable insight into its moulting behaviour and development, while their exceptional preservation enables detailed examination of cuticle microstructure. Moults were identified based on a repeated pattern of preservation characterised by the absence of the carapace, as a result of exuviation, and/or the absence of muscles, which are exceptionally well-preserved in carcasses. Among the 65 specimens of C. berberus, only eight moults were identified. These moults reveal a similar moulting mechanism to extant penaeids. Scanning electron microscopy revealed a thicker inner endocuticle than outer exocuticle, with one specimen showing what is likely the membranous layer. Lamination is present in the exo- and endocuticle, with fewer lamination present in the exocuticle, and the endocuticle generally shows laminae that are more widely spaced in the outer layers. No difference in cuticle lamination, luminescence or reflection were observed between carcasses and moults. Carapace lengths range from ∼2 to 20 mm, and a detailed morphological analysis of the smallest specimens revealed that early larval stages (nauplius, protozoeae) were absent, with the smallest individual being either a late postlarva or a juvenile. Morphological changes likely occurred during development from juvenile to adult, with adults having a proportionally longer and more spinous rostrum and proportionally longer antennae and elongated fourth and fifth pereiopods. The adults also exhibit pleopods with more equally sized rami that are more curled, annulated, thinner distally than in juveniles. C. berberus, a rare representative of freshwater-dwellers among penaeids and dendrobranchiates, is assessed for its potential development strategies in freshwater environments, in comparison with other freshwater decapod taxa in Pleocyemata.