A transapical undulation, or elevated ridge, of the external valve face. The porca is particular to the genus Surirella. Plural form is porcae. From Latin for an agricultural term meaning the “ridge between two furrows”.
transapical valve undulation
Bramburger, A.J., Haffner, G.D., Hamilton, P.B., Hinz, F. and Hehanussa, P.E. (2006). An examination of species within the genus Surirella from the Malili Lakes, Sulawesi Island, Indonesia, with descriptions of 11 new taxa. Diatom Research 21(1): 1-56. 10.1080/0269249X.2006.9705650
Karthick, B., Hamilton, P.B. and Kociolek, J.P. . (2012). Taxonomy and biogeography of some Surirella Turpin (Bacillariophyceae) taxa from Peninsular India. Nova Hedwigia, Beiheft 141: 81–116. 1438-9134/2012/0141 - 0081
Van de Vijver, B., Cocquyt, C., de Haan, M., Kopalová, K. and Zidarova, R. (2012). The genus Surirella (Bacillariophyta) in the sub-Antarctic and maritime Antarctic region. Diatom Research 28: 92-108. 10.1080/0269249X.2012.739975
Veselá, J., Johansen, J.R. and Potapova, M. (2013). Surirella terryi and S. cruciata: two rare diatoms in North America. Diatom Research . 10.1080/0269249X.2013.853697
Image Credit: Jana Veselá
Scanning electron micrograph of the external surface of a species within Surirella. A porca is outlined in white; a total of 2 porcae are visible in the image.
Image Credit: Marina Potapova
Scanning electron micrograph of the external surface of Surirella amphioxys. The raised portion of the undulation is a porca. The raised canal containing the raphe is at the top of the image.