Epithallus

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title: "Epithallus" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["red-algae"] topic_path: "general/red-algae" source: "https://en.wikipedia.org/wiki/Epithallus" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

The epithallium or epithallus is the outer layer of a crustose coralline alga, which in some species is periodically shed to prevent organisms from attaching to and overgrowing the alga.

Structure

It is defined as the cells above the intercalary meristem; these are not involved in photosynthesis. thicknesses of 16 cells or more, spanning 100 μm, have been measured in a representative coralline (Clathromorphum). The thickness is variable within species; in Lithothamnion, a single cell thickness is the norm, but three- or four-cell thick regions are also common. The epithallus sometimes overlies the roof of conceptacles, which are exposed only when the overlying epithallus is eventually shed.

The epithallium is less strongly calcified than the underlying cells, facilitating its removal. 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.

Function

Periodic sloughing of this surface is thought to reduce colonization of corallines by kelp (such as Laminaria), epiphytes, and sessile invertebrates. Epithallial cells are covered (in patches) by a cuticle. The deterioration of the outer cells is accelerated in the presence of bacteria.

Comparable structures

A similar mechanism is found in geniculate reds. Epidermal tissue is also shed by unrelated algae: the fleshy reds and browns, (e.g. Chondrus, Ascophyllum; Halidrys, Himanthalia{{cite journal | title = Epiphyte survival on skin-shedding macrophytes | author1= Russell, G |author2= Veltkamp, CJ | journal=Marine Ecology Progress Series | volume= 18 | issue= 1–2 | pages= 149–153 | year = 1984 | doi = 10.3354/meps018149 | bibcode= 1984MEPS...18..149R | doi-access= free

The epithallus probably originated from cover cells, which are considered to be homologous structures.

Refs

NB incomplete citations refer to references in Johnson & Mann (1986).

References

  1. (1986). "The crustose coralline alga, ''Phymatolithon'' Foslie, inhibits the overgrowth of seaweeds without relying on herbivores". Journal of Experimental Marine Biology and Ecology.
  2. (1966). "The genus ''Pseudolithophyllum'' (Corallinaceae) in the Gulf of Maine". Hydrobiologia.
  3. (1965). "The genus ''Clathromorphum'' (Corallinaceae) in the Gulf of Maine". Hydrobiologia.
  4. (1966). "The genera ''Lithothamnium'','' Leptophytum'' (nov. gen.) and ''Phymatolithon'' in the Gulf of Maine". Hydrobiologia.
  5. (1984). "The surface ultrastructure and epithallium shedding of crustose coralline algae in an 'Isoyake' area of southwestern Hokkaido, Japan". Hydrobiologia.
  6. Adey, W. H.. (1964). "The genus phymatolithon in the Gulf of Maine". Hydrobiologia.
  7. Adey, 1973; Johansen, 1981; Littler & Littler, 1984
  8. Padilla, 1981
  9. (1984). "Residual effects of grazing: inhibition of competitor recruitment by encrusting coralline algae". Ecology.
  10. (1985). "Ultrastructure of the vegetative thallus of ''Phymatolithon lenormandii'' (Aresch. in J. Ag.) Adey". Botanica Marina.
  11. (Borowitzka & Vesk, 1978)
  12. Filion-Myklebust, CC.. (1981). "Epidermis shedding in the brown seaweed ''Ascophyllum nodosum'' (L.) Le Jolis". Marine Biology Letters.
  13. (1981). "Seasonality of microbial fouling on ''Ascophyllum nodosum'' (L.) Lejol., ''Fucus vesiculosus'' L., ''Polysiphonia lanosa'' (L.) Tandy and ''Chondrus crispus'' Stackh". Journal of Phycology.
  14. Moss, B L. (1982). "The control of epiphytes by ''Halidrys siliquosa'' (L.) Lyngb. (Phaeophyta, Cytoseiraceae)". Phycologia.
  15. (1977). "Calcification in the green alga ''Halimeda''. I. An ultrastructure study of thallus development". Journal of Phycology.
  16. Jagels, R. H.. (1970). "Cell wall development in a marine monocotyledon". American Journal of Botany.

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