Determining the ecological niches of deep-sea fauna is critical in advancing our knowledge of the ocean. Previous studies attribute selective pressures, such as nutrient input, as the dominating factors influencing deep-sea ecology. Scale worms, ubiquitous invertebrates, display unique behaviours and ecological interactions in the deep-sea. In our study, we utilise an obligate deep-sea subfamily, known as Macellicephalinae, to determine how morphological traits are influenced by depth and habitat. We systematically mined the collection, biological and ecological data from the literature, and proceeded to conduct a meta-analysis. Firstly, we found that depth and feature type influence the length, width and segmentation of scale worms. Second, functional traits indicate both specialisation and niche partitioning within deep-sea features, particularly in highly sampled features such as hydrothermal vents. Thirdly, there are few differences in traits within ocean zones, however, the hadal zone seems to differ from that of shallow, bathyal and abyssal zones. Our study highlights the adaptive plasticity of the Macellicephalinae group and explains their dominance of the deep-sea.