[5] It lived during the late Lower Cambrian, with remains found in Canada (Newfoundland & Labrador), the United States (Massachusetts, New York State), Greenland, The United Kingdom (England), Sweden, France, Germany, Italy (Sardinia), Kazakhstan, the Russian Federation and China.

The type species by original designation is Agnostus lobatus Hall, 1847 from the upper part of the lower Cambrian Browns Pond Formation (formerly Schodack Formation) at Troy in the Taconic region of New York State, USA [= Calodiscus korolevi Pokrovskaya in Ergaliev and Pokrovskaya, 1977; Calodiscus lakei Rasetti, 1952; and Calodiscus n. sp.

[6][7] Lochman (1956)[8] demonstrated that Calodiscus agnostoides (Kobayashi, 1943) represents late meraspid instars of C. lobatus (Cederström et al., 1988, p. 500).

Of four named Calodiscus species from the Lower Cambrian of the Siberian Platform revised by Korovnikov and Bushuev (2024)[9] only two, C. resimus Repina, 1972 and C. schucherti (Matthew, 1896) were retained in the genus.

C. helena (Walcott, 1889)[10] and C. granulosus Jegorova et Shabanov, 1972 (Korovnikov and Bushuev, op cit.)