In algal anatomy, a pit connection is a hole in the septum between two algal cells, and is found only in multicellular red algae[1] − specifically in the subphylum Eurhodophytina, except haploid Bangiales.
By contrast, many fungi (only ascomycetes and basidiomycetes, as most other groups lack septa) contain septal pores − an unrelated phenomenon.
[3] A sieve-like membrane may cover the pit in living algae,[4] but in the majority of algae a plug forms, they likely limit the transfer of metabolites between neighbouring cells.
[4] Such connections are always single, and usually circular;[4] 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.