[2] In Phymatolithon, the epithallium is usually one cell thick,[2] whereas in other genera, such as Pseudolithophyllum, multiple cells exist, with the thickness determined by the difference between their rate of production at the intercalary meristem, and the rate of shedding at the surface;[3] thicknesses of 16 cells or more, spanning 100 μm, have been measured in a representative coralline (Clathromorphum).
The meristem itself is the least calcified portion; sometimes there is no mineralization at all, which makes it a plane of weakness where breaking often occurs.
[4] Periodic sloughing of this surface is thought to reduce colonization of corallines by kelp (such as Laminaria),[6] epiphytes,[2][3][7] and sessile invertebrates.
[11] Epidermal tissue is also shed by unrelated algae: the fleshy reds and browns,[12] (e.g. Chondrus, Ascophyllum;[13] Halidrys,[14] Himanthalia[15]) and the calcaerous greens.
[16] Some sea grasses also periodically shed their external cell walls to avoid epiphyte cover.