membranelles

Membranelles are specialized, compound ciliary structures found in a subset of ciliates, a group of single-celled eukaryotes in the phylum Ciliophora. They consist of densely packed cilia that are often fused or tightly coordinated to form a membrane-like sheet or belt around the oral region. This arrangement creates an oral ciliature capable of generating directed water currents that help bring prey toward the cell’s cytostome (mouth).

In many ciliates, particularly the hypotrichs and certain oligotrichs, membranelles are organized into an adoral zone of membranelles (AZM) surrounding the oral opening. The AZM may include several membranelles arranged in a semicircular or circular arc, and is sometimes accompanied by additional membranellar rows along the buccal groove, such as paroral and endoral membranelles. The exact number and arrangement of membranelles vary among taxa, but the basic unit remains a functional bundle of cilia acting as a single beating apparatus.

Functionally, membranelles drive feeding currents and facilitate the capture of food particles, drawing bacteria, algae, and other small prey toward the cytostome for ingestion. They may also contribute to motility as part of the broader ciliature in some species.

Membranelles are a characteristic feature used in the description and classification of ciliates. The presence and specific organization of membranellar zones contribute to distinguishing groups within the ciliates, reflecting variations in oral apparatus and feeding strategies across taxa.