Dr. Ernest Marcus was a well accomplished German malacologist who did much of his research out the University of São Paulo, Brazil. He was a prolific writer who published on a wide range of topics in marine biology, with an emphasis on American Opisthobranchs. He often published with his wife, Eveline du Bois Reymond Marcus; their names are sometimes abbreviated as E. & E. Marcus, or Er. and Ev. Marcus (for Ernest and Eveline, respectively).

Relevant to the biota of the Gulf of Mexico, Ernest Marcus has published the following:

Marcus, E. 1961. Opisthobranchia from North Carolina. Journal of the Elisha Mitchell Scientific Society 77(2): 141–151.
Marcus, E., and E. d. B.-R. Marcus. 1970. Opisthobranchs from Curaçao and faunistically related regions. Studies on the Fauna of Curaçao and other Caribbean Islands 33(122): 1–129.
Marcus, E. d. B.-R. 1971. Opisthobranchs from northern Brazil. Bulletin of Marine Science 20(4): 922–951.
Marcus, E. d. B.-R. 1972a. On some opisthobranchs from Florida. Bulletin of Marine Science 22(2): 284–308.
Marcus, E. d. B.-R. 1972b. Notes on some opisthobranch gastropods from the Chesapeake Bay. Chesapeake Scientist 13(4): 300–317.
Marcus, E. d. B.-R. 1972c. On the Anaspidea (Gastropoda: Opisthobranchia) of the warm waters of the Western Atlantic. Bulletin of Marine Science 22(4): 841–874.
Marcus, E. d. B.-R. 1974. On some Cephalaspidea (Gastropoda: Opisthobranchia) from the western and middle Atlantic warm waters. Bulletin of Marine Science 24(2): 300–371.
Marcus, E. d. B.-R. 1976. Opisthobranchia von Santa Marta, Colombia. Studies on Neotropical Fauna and Environment 11(1–2): 119–150.
Marcus, E. d. B.-R. 1977a. On the genus Tornatina and related forms. Journal of Molluscan Studies, Supplement 2: 1–35.
Marcus, E. d. B.-R. 1977b. An annotated checklist of the Western Atlantic warm water opisthobranchs. Journal of Molluscan Studies, Supplement 4: 1–22.
Marcus, E. d. B.-R. 1978. The Western Atlantic species of Onchidella (Pulmonata). Sarsia 63(4): 221–224.
Marcus, E. d. B.-R. 1980. Review of Western Atlantic Elysiidae (Opisthobranchia Ascoglossa) with a description of a new Elysia species. Bulletin of Marine Science 30(1): 54–79.
Marcus, E. d. B.-R. 1983. The Western Atlantic Tritoniidae. Boletim de Zoologia, Universidade de São Paulo 6: 117–214.
Marcus, E. d. B. R., and S. B. Gallagher. 1976. A new species of Dendrodoris from Florida. The Veliger 18(4): 353–356, 1 pl.
Marcus, E. d. B. R., and T. M. Gosliner. 1984. Review of the family Pleurobranchaeidae (Mollusca: Opisthobranchia). Annals of the South African Museum 93(1): 1–52.
Marcus, E. d. B. R., and H. P. I. Hughes. 1974. Opisthobranch mollusks from Barbados. Bulletin of Marine Science 24(3): 498–532.
Marcus, E. [d. B.-R.], and E. Marcus. 1960a. Opisthobranchs from American Atlantic warm waters. Bulletin of Marine Science of the Gulf and Caribbean 10(2): 129–203.
Marcus, E. [d. B.-R.], and E. Marcus. 1960b. Some opisthobranchs from the northwestern Gulf of Mexico. Publications of the Institute of Marine Sciences, University of Texas 6: 251–264.
Marcus, E. [d. B.-R.], and E. Marcus. 1962. Opisthobranchs from Florida and the Virgin Islands. Bulletin of Marine Science of the Gulf and Caribbean 12(3): 450–488.
Marcus, E. [d. B.-R.], and E. Marcus. 1967a. Opisthobranchs from the southwestern Caribbean Sea. Bulletin of Marine Science 17(3): 597–628.
Marcus, E. [d. B.-R.], and E. Marcus. 1967b. Tropical American opisthobranchs. Studies in Tropical Oceanography 6: 1–137.
Marcus, E. [d. B.-R.], and E. Marcus. 1967c. Some opisthobranchs from Sapelo Island, Georgia, U. S. A. Malacologia 6(1–2): 199–222.