Theelia was named by Schlumberger (1890) [Sepkoski's age data: C Bash R Sepkoski's reference number: 1066]. It is extant. It is considered to be a form taxon. Its type is Chirodota undulata. It is the type genus of Theeliidae. It was considered polyphyletic by Gilliland (1992), Gilliland (1993).

It was synonymized subjectively with Chiridotites by Deflandre-Rigaud (1957).

It was assigned to Apoda by Schlumberger (1890); to Theelidae by Summerson and Campbell (1958), Górka and Luszczewska (1969); to Theeliidae by Said and Barakat (1958), Frizzell and Exline (1966), Garbowska and Wierzbowski (1967), Speckmann (1968), Zawidzka (1971), Kozur and Mostler (1971), Mostler (1971), Mostler (1972), Kristan-Tollmann (1972), Mostler and Parwin (1973), Mostler and Rahimi-Yazd (1976), Soodan and Whatley (1988), Kozur and Mostler (1989), Kozur and Sadeddin (1990), Soodan (1991), Henderson et al. (1992), Krainer and Mostler (1997); to Apodida by Gilliland (1992), Gilliland (1993), Sepkoski (2002); and to Chiridotidae by Reich and Wiese (2010).