In algal anatomy, a pit connection is a hole in the

septum In biology, a septum (Latin for ''something that encloses''; plural septa) is a wall, dividing a cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate. Examples Human anatomy * Interat ...

between two algal cells, and is found only in the

red algae Red algae, or Rhodophyta (, ; ), are one of the oldest groups of eukaryotic algae. The Rhodophyta also comprises one of the largest phyla of algae, containing over 7,000 currently recognized species with taxonomic revisions ongoing. The majority ...

− specifically, all orders except the Porphyridiales and haploid Bangiales. They are often stoppered with proteinaceous "pit plugs". By contrast, many

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately fr ...

(only ascomycetes and basidiomycetes, as most other groups lack septa) contain septal pores − an unrelated phenomenon.

Characteristics

A sieve-like membrane may cover the pit in living algae, but in the majority of algae a plug forms, they likely limit the transfer of metabolites between neighbouring cells.

Formation

Primary pit connections are formed between cells in the same filament, derived from the same parent cell by its division. Such connections are always single, and usually circular; this is a result of their method of formation. The septum is formed as the walls of a filament grow inwards, dividing the cell; this results in a hole in the middle of the tube where the walls don't quite merge. Thus pit connections are visible in the youngest of septa, widening as the septum thickens, until in some cases they may ultimately occupy the entire septum. Secondary connections, by contrast, occur between unrelated cells, and serve a role in transferring cell contents and nutrients. They may even form between cells of different species, as in the parasite '' Holmsella''.

References

External links

* Transverse SEM images of pit connections in the coralline ''

Synarthrophyton ''Synarthrophyton'' is a genus of thalloid red algae comprising eight species. The monomerous, crustose thalli are composed of a single system of filaments which grow close to the underlying surface. ''Synarthrophyton'' reproduces by means of fl ...

'' can be seen in Figs. 54 & 60 in * (Lower quality) transverse SEM images of pit connections in the coralline ''

Phymatolithon ''Phymatolithon'' is a genus of non geniculate coralline red algae, known from the UK, and Australia. It is encrusting, flat, and unbranched; it has tetrasporangia and bisporangia borne in multiporate conceptacle Conceptacles are specialized ...

'' are available on page 138 at . {{Protist structures Red algae