What are mud dragons (Kinorhyncha), and why are they interesting?


Maria Herranz

Department of Biology, University of Copenhagen, Denmark


Kinorhyncha is a clade of marine, microscopic organisms, part of the ‘molting animals’ known as Ecdysozoa. Despite having been described for more than a century, kinorhynchs are severely understudied counting on less than a handful of experts across the globe. Hence, basic questions about their biology, diversity, and evolution still remain to be answered. One of the most interesting topics, and in which I will focus during my talk is segmentation.

The kinorhynch body plan consists on a radially symmetrical retractable head, a neck, and a limbless trunk with distinct segmentation. Within the Ecdysozoa, segmentation is only present in Panarthropoda (including arthropods, onychophorans and tardigrades) and Kinorhyncha, which is closely related to unsegmented lineages (Priapulida, Loricifera, Nematoida). Kinorhynchs may provide an important example of convergent evolution of segmental patterns within ecdysozoans and therefore, the study of their internal anatomy is crucial for understanding the origin of segmentation in ecdysozoans. However, comparative studies on the musculature and the nervous system across Kinorhyncha, using immunohistochemistry and confocal laser scanning microscopy, have shown that the segmentation patterns may vary, and in some taxa be less distinct. A better anatomical understanding of these aberrant kinorhynchs combined with phylogenomic data has helped us unravel the evolution of segmentation within Kinorhyncha, as well as the relation to non-segmented body plans in Scalidophora.