Folks who have heard me talk about Mastigusa macrophthalma (the "Charnwood Spider") will know that I'm dubious about the identity of this spider, and indeed about the validity of M. macrophthalma as a species. A recent paper takes a close look at Mastigusa from across Europe ... and doesn't solve the problem. The good news is that Mastigusa appears to be a solid genus, dating back 45 million years. I'll let the authors give you the bad news in their own words:
"Morphology-wise, the clade composed by specimens from Southern Spain and the United Kingdom (and the single specimen from the Pyrenees), do not fit with any of the currently described Mastigusa species, showing marked differences with the observed type-material, mostly regarding the morphology of the male palp. Iberian populations have always been considered as M. arietina, while in the United Kingdom both M. arietina and M. macrophthalma have been historically reported, but again only based on eyes characters. The overall morphology and dimensions for these specimens, and their distribution fit with M. arietina, but the male palp consistently shows marked differences with all the other specimens observed. Our molecular data strongly suggests that these specimens could belong to a new, previously overlooked, Mastigusa species."
As a taxonomic lumper I haven't changed my opinion that we're probably dealing with Mastigusa arietina, but something seems to have happened 19 million years ago which shook this genus up. My geology isn't good enough to speculate that that may have been.
Castellucci, F., Scharff, N., & Luchetti, A. (2023) Molecular systematics and phylogenetics of the spider genus Mastigusa Menge, 1854 (Araneae, Cybaeidae). Molecular Phylogenetics and Evolution, 107833.
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