After its initial discovery by French zoologist Émile Topsent in Concarneau, France, in 1896, Thymosia guernei remained elusive until it was rediscovered through dredging off Plymouth's Mewstone Grounds in 1956.

The sponge features a few small oscules scattered along ridges and lobes, often occupied by crustaceans and brittle stars, while countless microscopic pores cover the surface.

[3] The sponge lacks a mineral skeleton; instead, it features a robust cortex abundantly reinforced by fibrillar collagen, enhancing the otherwise soft matrix.

Spongin fibers, characterized by unique kidney-shaped swellings, provide additional strength by vertically traversing the body to the surface, where they branch and anastomose at distinct intervals.

Additionally, it is occasionally found off the mainland, such as in North Pembrokeshire (off Abereiddy), St. Johns Point in County Donegal, France (Concarneau), and Portugal (Algarve).