The scientists, per The Science of Nature, noted some crucial differences between the original body parts and those that had grown afterward. “In the unharmed body half, the ovaries occupy the space lateral and dorsal to the gut throughout the trunk with its segmental lateral processes,” they state, while “the area of the fused right lateral processes and the fused coxae 1 comprises a relatively large dorsal area in which no part of the ovary or oocytes can be found … there is an open space that is only loosely filled with unspecified connective tissue.”
Per the study, regeneration of body parts can easily lead to anomalies, depending on the region and the reasons for it. Nonetheless, the very fact that this creature was able to regenerate something that was so much more than just a leg is extraordinary. The scientists also explain that they don’t know the extent of the original damage, so it’s unclear how it influenced this growth and in what way as the sea spider grew.
The January 2023 study “The sea spider Pycnogonum litorale overturns the paradigm of the absence of axial regeneration in molting animals,” from Georg Brenneis et al. (via the Proceedings of the National Academy of Sciences of the United States of America) states that this was no one-off. Following amputations of immature specimens of the Pycnogonum litorale species of sea spider, it was found that they can “regrow almost complete segments and the terminal body region, including the hindgut, anus, and musculature.”
