Microboring traces in carbonate skeletal fragments deposited in aphotic depths of the oceans are studied, evaluated, and described with respect to their marine ecology and palaeoecology as well as ichnotaxonomy. Sand-size deep sea sediment particles dredged from depths ranging between 600 and 3266 m of the Bermuda Pedestal, Central Atlantic Ocean, the Florida Escarpment, the Mediterranean Sea, the Red Sea and the Indian Ocean were studied. Following ichnological rules, trace fossils are described as ichnogenera and ichnospecies, defined as products of organismal behaviour. This, in our view, refers to the growth habit of microboring organisms in response to environmental stimuli within the substrate they penetrate. The problem of palaeobathymetry is discussed in conjunction with the distinction between light-dependent and light independent microboring organisms, with the emphasis on the latter. We considered this distinction to be important because only the light-dependent microborers have been recognized as indicators of ancient depositional depths, whereas the light-independent ones are expected to occur at any depth, subject to the availability of organic nutrients. Microboring organisms often leave morphologically similar traces due to convergent evolution. Their responses may change during their life cycle; they may produce different traces when pursuing their vegetative vs. reproductive functions. New ichnotaxa are described. All are regarded as organotrophs given their aphotic zone deep sea origin. This work presents the most complete set of deep sea microbial euendolith traces, to date.