How to assess the absence of a species? A revision of the geographical range of the horned sea star, Protoreaster nodosus (Echinodermata; Asteroidea)

Demonstrating the absence of a species has always been a challenge for natural sciences, which are more used to documenting their presence; however, both forms of data are of equal scientific significance. The horned sea star Protoreaster nodosus is said, in the scientific literature, to be present throughout the whole Indo-Pacific region, from eastern Africa to the Pacific Ocean islands. However, a review of the scientific literature, along with a critical bibliographical study, citizen science surveys, web-based pictures analyses, and field studies suggests that the presence of this species could instead be restricted to the western Pacific Ocean, from Thailand to Samoa and from Japan to New Caledonia, with no reliable record in the Indian Ocean. Such a huge and long-running mistake on a very common and conspicuous species exemplifies the importance of a critical approach towards species distribution data, which appears too often based on layers of reproduction of never-reassessed data, turning hypotheses into commonly shared truth.