Maiocercus celticus is a species of early trigonotarbid arachnid from the Upper Carboniferous of Westhoughton, Lancashire, UK.

[1][2] M. celticus is the type species of the genus Maiocercus.

[3] Originally zoologist Reginald Innes Pocock compared M. celticus to Brachypyge, with later evidence showing that Brachypyge had "opisthosoma which were much longer than wide; with the pleural laminæ of the second and third pleura-bearing terga being inclined slightly backwards" (Brachypyge) with Maiocercus having the “opisthosoma much wider than long; the pleural laminæ of the first, second, third, and fourth sterna being inclined slightly forwards”.

[4] The original drawing which showed Maiocercus described a pitting on the underside of the slightly forwarded laminæ, with a non-uniform concavity on the outer margins of them.

The concavity is most well-marked in the fifth, sixth, seventh and eighth somites, with the opposite happening on the second, third and fourth somites.