ciliadas

Ciliadas, commonly referred to as ciliates in English, are a diverse group of single-celled eukaryotes characterized by the presence of cilia at some life stage, used for locomotion and feeding. They belong to the phylum Ciliophora within the supergroup Alveolata and include a wide range of free-living, symbiotic, and parasitic species. Ciliates inhabit a variety of environments, from freshwater and marine ecosystems to soil and the bodies of other organisms.

A hallmark of ciliates is their dual nuclear organization: a macronucleus that governs everyday cellular functions and a micronucleus that serves as a genetic reservoir used in sexual processes. Their cells typically possess an elaborate oral apparatus, including structures such as the cytostome and membranelles, which funnel food particles into the cell. Many species also feature a contractile vacuole system to regulate water balance and maintain osmotic stability. The ciliary apparatus, organized as ciliature, powers movement and directs prey toward the mouth region.

Reproduction is primarily asexual through binary fission, though ciliates can engage in genetic exchange via conjugation, and some undergo autogamy. Ecologically, they play a central role in microbial food webs by consuming bacteria and other small protists, contributing to nutrient recycling. They are widely used as model organisms in biology (for example, Paramecium and Tetrahymena) due to their relatively large nuclei, ease of cultivation, and distinctive cellular features. Taxonomically, ciliates are grouped into multiple classes, including Spirotrichea, Oligohymenophorea, Litostomatea, and others, reflecting their diversity across aquatic and semi-aquatic habitats.