Heterovalvar

Heterovalvar refers to frustules in which one valve differs from the other morphologically. Frustules may be heterovalvar in their valve ornamentation or their raphe system. Heterovalvar is often applied to the monoraphid diatoms, in which one valve has a normal raphe and the other is rapheless.

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.

Platessa Conspicua Example — The species *Platessa inconspicua* is an example of a heterovalvar diatom. One valve has a raphe system and the other valve lacks it. This species is also heterovalvar because of such characters as the morphological differences of the central areas of the two valves.