Hemivalve

Hemivalve refers to the portion of a diatom valve on either side of the apical axis of the valve face. In pennate diatoms, the central sternum and raphe are positioned on the apical axis, with a "hemivalve" on either side of the axis. In some groups, the apical axis does not align with the sternum (Nitzschia, Pseudo-nitzschia), forming a "minor hemivalve" with less area than a "major hemivalve".

In radially symmetric polar diatoms, the axis extends through the poles and valve center (Bellerochea and Lithodesmioides in Yahia-Kefi et al. 2005).

Citations

Accoroni, S., Giulietti, S., Romagnoli, T., Siracusa, M., Bacchiocchi, S. and Totti, C. (2020) Morphological variability of Pseudo-nitzschia pungens clade I (Bacillariophyceae) in the northwestern Adriatic Sea Plants 9: 1420.

Publication Link: 10.3390/plants9111420
Daly Yahia-Kéfi, O., Souissi, S., De Stefano, M. and Yahia, Daly M.N. (2005) Bellerochea horologicalis and Lithodesmioides polymorpha var. tunisiense var. nov. (Coscinodiscophyceae, Bacillariophyta) in the Bay of Tunis: ultrastructural observations and spatio-temporal distribution. Botanica Marina 48: 58-72
Romero, O. and Jahn, R. (2013) Typification of Cocconeis lineata and Cocconeis euglypta (Bacillariophyta) Diatom Research 28(2): 175-184

Publication Link: 10.1080/0269249X.2013.770801

Pseudo-nitzschia hemivalve — Red line along the axis of this valve of *Pseudo-nitzschia* separates the two hemivalves. White arrow marks the raphe. The raphe side is the major hemivalve. Scale bar = 10 µm.

C czarneckii hemivalve — Raphe and rapheless valves of *Cocconeis czarneckii* (SEM). Red lines separate the hemivalves. Scale bar = 10 µm.

hydrosera-whampoensis-hemivalve — Valve of *Hydrosera whampoensis*, a polar centric diatom. Red line separates the hemivalves. Scale bar = 10 µm.