Segments of the scorpion metasoma described for the first time

A team of researchers at Institut für Biowissenschaften, the University of Tübingen, Muséum d'histoire Naturelle and Route de Malagnou has fully described the anatomy of the scorpion metasoma for the first time in their paper published in Journal of the Royal Society Interface.

Scorpions have a segmented appendage on their back end called a metasoma, used to sting, hunt prey, mate, dig and defecate. Its anus is also on the metasoma, as are its intestines and ventral nerve cord. In this new effort, the researchers noted that despite the scorpion's fame, its metasoma (which is not a tail) has never been fully described, and because of that, they set out to learn more about the unusual appendage.

The researchers began their work by comparing the metasoma of 16 scorpion species. They found differences in characteristics of the appendage, such as thickness or length, but not in overall structure. They next chose a specimen for closer study, a female Mesobuthus gibbosus. They first scanned her metasoma using CT imaging. They then used the results to reconstruct it in virtual 3D imaging and then followed that up by printing larger-than-actual-size 3D versions of it, which they could manipulate with their hands.

They found that the appendage had five segments, each of which was a tube made up of a strong cuticle material. The tubes were connected by joints that have not been described before. They identified them as similar to a ball and socket joint but with a saddle-type structure instead of a socket. Such joints allow the scorpion to bend its metasoma while simultaneously twisting it at the segments. Researchers called them a "sliding rolling pair." They note that they were unable to ascertain whether the joint slides or rolls, but they plan to investigate it further in continuing studies of scorpions in general. They note also that that the fifth segment, the one on the end that holds the stinger, can only be bent not twisted.

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