Callianassoid burrowing ghost shrimps are mostly small animals, with a total length (from the tip of the rostrum to the end of the tailfan) typically not exceeding a few centimetres. Representatives of some species in the families Anacalliacidae, Callianassidae, Callichiridae, Ctenochelidae, and possibly also Callianopsidae, however, may grow to relatively large sizes, reaching 10 and more centimetres in length. The maximum size each of these species can attain remains a mere estimate because it is difficult to catch ghost shrimps, particularly the large-sized tropical representatives. Since large individuals have a greater fossilization potential, the ghost shrimp fossil record could contribute to our knowledge about how large these animals can grow. The largest extant ghost shrimp reported to date is an individual of the species Glypturus armatus (Callichiridae), with an estimated total length of 175 mm (based on the extrapolation from an isolated ischium). The existence of even larger animals reaching a total length of approximately 200 mm is documented herein from the Maastrichtian of Madagascar and the middle Eocene of Hungary, with both fossil individuals belonging to the genus Karumballichirus (Callichiridae) and appearing to be closely related to the extant Karumballichirus karumba. An overview of both extant and fossil ghost shrimp species suggests that a total length of 200 mm is rarely, if ever, exceeded by these animals. We suggest that physiological limits imposed by the specialized burrowing lifestyle might prevent ghost shrimp from growing any larger.

Key words: Malacostraca, Decapoda, Axiidea, body length, burrowing shrimps, decapod crustaceans, fossilization potential, physiological limits.

Matúš Hyžný [hyzny.matus@gmail.com; ORCID: https://orcid.org/0000-0002-8960-2846], Department of Geology and Paleontology, Faculty of Natural Sciences, Comenius University, Ilkovičova 6, SK-842 15 Bratislava, Slovakia. Dominik Kneer [dmkneer@gmail.com; ORCID: https://orcid.org/0000-0001-9874-4793], Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Wadden Sea Station Sylt, Hafenstraße 43, D-25992 List, Germany. Sylvain Charbonnier [sylvain.charbonnier@mnhn.fr; ORCID: https://orcid.org/0000-0003-2343-6897], Centre de Recherche en Paléontologie – Paris (CR2P, UMR 7207), CNRS-MNHN-Sorbonne Université, Muséum national d’Histoire naturelle, 8 rue Buffon, Paris, France.