Abstract
Glass sponges (Porifera: Hexactinellida) have been the subject of scientific investigation for over two centuries, yet the temporal and thematic structure of this research effort has never been quantitatively evaluated. Here, we assessed taxonomic activity, geographical and bathymetric coverage, and keyword trends extracted from the indexed literature. We found two different periods of intense taxonomic activity occurring in the late 19th century and early 20th century, and then following World War II, with a steady increase in currently indexed publication output following the establishment of the modern peer-review system. However, research has been disproportionately concentrated on mesophotic and bathyal depths, whereas shallow and abyssal glass sponges have received comparatively little attention, while hadal records remained largely confined to the non-indexed literature until very recently. Furthermore, we found a decline in the number of active experienced glass sponge taxonomists, with few new experts being trained. This mismatch occurs as abyssal and hadal environments become increasingly accessible, potentially constraining our ability to adequately study the taxonomy and ecology of ultra-deep glass sponges.