The detection and identification of the species living on a given area is usually supposed to provide a corpus of basic knowledge enabling biologists to develop further pieces of knowledge. However, it reveals surprisingly difficult to achieve biological inventories satisfying the criteria pertaining to such basic knowledge. Our aim in this paper is to highlight how the current practice of biological inventory is shaped by various constraints and potential biases. This leads us to re-consider the functions of inventories at the (...) beginning of the twenty-first century. In order to do so, we present the example of deep-sea fauna inventories in the Pacific Ocean. We focus on one source of bias in this case: the lasting influence of the so-called “azoic hypothesis”, formulated in the 1840s, according to which there is no life under 600 meters. We show how the azoic hypothesishas strongly influenced the conception of deep-sea fauna even though it has been quickly refuted. At the end of the paper, we look into the implications of economical constraints on the current practice of deep-sea biological inventory. (shrink)