Farabee, M. J. (2007). THE CIRCULATORY SYSTEM. Retrieved March 6, 2017, from https://www2.estrellamountain.edu/faculty/farabee/biobk/BioBookcircSYS.html
Parent, C. E. (2008). The Global Decline of Mollusks. Retrieved March 6, 2017, from http://www.actionbioscience.org/biodiversity/parent.html
Solem, G. A. (2015, March 20). Gastropod. Retrieved March 6, 2017, from https://www.britannica.com/animal/gastropod/The- foot#ref413151
Visceral hump. (n.d.). Retrieved March 6, 2017, from https://www.britannica.com/science/visceral-hump