From the Super Mario Wiki
Terra Cottas are advanced versions of the Terrapin soldiers that appeared in Bowser's Keep in Super Mario RPG: Legend of the Seven Stars. Their name comes from "Terrapin", but is also a pun on the ceramic terra cotta. As well as having red shells, Terra Cottas further distinguish themselves from their green-shelled Terrapin brethren by wielding swords in battle. Though they changed sides and worked for the Smithy Gang, they are easily scared off by Bowser, which is very helpful, as they are very strong.
Names in other languages
|Koopa Soldier Red (Nokohei is the Japanese name of Terrapins; Reddo is a transliteration of the English "red")