Frailea castanea

From the Latin name “Castanea” which means “chestnut” and refers to dark reddish-brown colour. (the Latin "Castanea" derives  f rom the Greek. "kastaneia", which meant either "nut from Castanea" in Pontus (eastern Greece) or "nut from Castana" in Thessaly, but probably both places are named for the trees, and the word is probably borrowed from a language of Asia Minor.

( The specific name implies: "coloured like a chestnut").

For example Frailea castanea