Most of the cells in a multicellular organism possess cilia. In eukaryotes, one or two cilia generally considered as sensory while tens and hundreds of cilia per cell are usually motile. Multiciliated cells (MCCs) activity drive fluid flow across an epithelium thus allow motility and feeding in small invertebrates and their swimming larvae as well as organize mucus clearance, cerebrospinal fluid circulation, and egg transportation in vertebrates. Molecular mechanisms of ciliogenesis and regulation of ciliary length are much conserved among the phyla. And MCCs dysfunction is associated with numerous diseases and loss of function in both vertebrates and invertebrates. While the initial stage of cilia formation and maintenance are studied in details less is known about the period of their loss of function during aging. Here, we present the marine polychaete Dinophilus gyrociliatus as a unique model to study mechanisms of age-related changes in ciliary cell structure. We demonstrated a decrease in cilia number per cell as well as a ciliary shortage in multiciliated cells on senior individuals of D. gyrociliatus while it was maintained in juveniles and adults. As a result, the ciliary driving locomotion of aged individuals drastically slowed down. The advantages of D. gyrociliatus are short life span, permeable epithelium, sequenced genome and easily rearing in culture. Our results demonstrate that D. gyrociliatus represents a perspective model to investigate cilia growth and age-related changes in both normal conditions and under various environmental and pharmacological influences. The study was supported by RFBR, projects # 19-34-60040 and #18-04-01213.