A new species of Mesostylus (Decapoda, Axiidea, Callianassidae) – a peep into the private life of a Late Cretaceous burrowing shrimp

Numerous individuals of a ghost shrimp, here described as a new species, Mesostylus pervesleri, are recorded from the lower Maastrichtian Piesting Formation at Muthmannsdorf in Lower Austria. The accompanying molluscan fauna comprises bivalves, gastropods and cephalopods that are indicative of a low-energy, shallow-marine environment with normal salinity. The ghost shrimp body fossils are associated with two types of trace fossil; one of these is here interpreted as the remains of a callianassid burrow system, a conclusion supported by the in-situ preservation of body fossils within the burrows. Occasionally more than one individual is preserved in the same burrow structure; specimen orientation suggests that these represent moults. The presumed moults from the same burrow structure apparently do not belong to the same individual, which supports the idea that more animals shared the same burrow system at any time. Gregarious behaviour amongst representatives of the extinct genus Mesostylus is postulated on the basis of this find, and a similar one from the Upper Cretaceous of Germany. The diagnosis of the genus Mesostylus is here emended to include characters of the pleon and telson as documented not only in the new material from Muthmannsdorf but, more importantly, also in the type species, Mesostylus faujasi. The type material of Protocallianassa sarysuensis from the Coniacian of Azerbaijan is reinterpreted as representing the minor chelae of a co-occurring species, Protocallianassa caucasica; together they are here referred to as Mesostylus caucasicus, which brings the number of species belonging to the genus to four.