The sea spider overturns the paradigm of the absence of axial regeneration in molting animals.

Regenerative abilities and their evolution in the different animal lineages have fascinated generations of biologists. While some taxa are capable of restoring entire individuals from small body fragments, others can regrow only specific structures or lack structural regeneration completely. In contrast to many other protostomes, including the segmented annelids, molting animals (Ecdysozoa) are commonly considered incapable of primary body axis regeneration, which has been hypothesized to be linked to the evolution of their protective cuticular exoskeleton.

A microCT-based atlas of the central nervous system and midgut in sea spiders (Pycnogonida) sheds first light on evolutionary trends at the family level.

Background: Pycnogonida (sea spiders) is the sister group of all other extant chelicerates (spiders, scorpions and relatives) and thus represents an important taxon to inform early chelicerate evolution. Notably, phylogenetic analyses have challenged traditional hypotheses on the relationships of the major pycnogonid lineages (families), indicating external morphological traits previously used to deduce inter-familial affinities to be highly homoplastic. This erodes some of the support for phylogenetic information content in external morphology and calls for the study of additional data classes to test and underpin in-group relationships advocated in molecular analyses.