Ligula

A ligula is a silica projection on a split ring girdle band. The ligula of a younger girdle band fills, or nearly fills, the gap caused by the split in the older band next to it. In Latin, ligula means strap. The plural is ligulae. The girdle bands of many diatom taxa have ligulae.

Citations

Round, F.E., Crawford, R.M. and Mann, D.G. (1990) The Diatoms. Biology and Morphology of the Genera. Cambridge University Press, Cambridge, 747 pp.
Cox, E.J. (2011) Morphology, cell wall, cytology, ultrastructure, and morphogenetic studies. Overview and specific observations. In: The Diatom World (J. Seckbach and J.P. Kociolek, Eds,), Cellular origin, life in extreme habitats and astrobiology, Vol. 19, pp. 21–45, Springer, Dordrecht.