Thalassinoides

Thalassinoides is an ichnogenus of trace fossil used to refer to "dichotomously or T-branched boxworks, mazes and shafts, unlined and unornamented". Facies of "Thalassinoides" increased suddenly in abundance at the beginning of the Mesozoic. Such burrows are made by a number of organisms, including the sea anemone "Cerianthus", "Balanoglossus" and fishes, but are most closely associated with decapod crustaceans of the (former) infraorder Thalassinidea.