Cilium in the context of Kinocilium

The archaellum (pl.: archaella; formerly archaeal flagellum) is a unique structure on the cell surface of many archaea that allows for swimming motility. The archaellum consists of a rigid helical filament that is attached to the cell membrane by a molecular motor. This molecular motor – composed of cytosolic, membrane, and pseudo-periplasmic proteins – is responsible for the assembly of the filament and, once assembled, for its rotation. The rotation of the filament propels archaeal cells in liquid medium, in a manner similar to the propeller of a boat. The bacterial analog of the archaellum is the flagellum, which is also responsible for their swimming motility and can also be compared to a rotating corkscrew. Although the movement of archaella and flagella is sometimes described as "whip-like", this is incorrect, as only cilia from Eukaryotes move in this manner. Indeed, even "flagellum" (word derived from Latin meaning "whip") is a misnomer, as bacterial flagella also work as propeller-like structures.

Early studies on "archaeal flagella" identified several differences between archaella and flagella, although those differences were dismissed as a possible adaptation of archaella to the extreme ecological environments where archaea were at the time known to inhabit. When the first genomes of archaeal organisms were sequenced, it became obvious that archaea do not code for any of the proteins that are part of the flagellum, thus establishing that the motility system of archaea is fundamentally different from that of bacteria. In order to highlight the difference between these two organelles, the name archaellum was proposed in 2012 following studies that showed it to be evolutionarily and structurally different from the bacterial flagella and eukaryotic cilia.

Eukaryogenesis, the process which created the eukaryotic cell and lineage, is a milestone in the evolution of life, since eukaryotes include all complex cells and almost all multicellular organisms. The process is widely agreed to have involved symbiogenesis, in which an archaeon and one or more bacteria came together to create the first eukaryotic common ancestor (FECA). This cell had a new level of complexity and capability, with a nucleus, at least one centriole and cilium, facultatively aerobic mitochondria, sex (meiosis and syngamy), a dormant cyst with a cell wall of chitin and/or cellulose and peroxisomes. It evolved into a population of single-celled organisms that included the last eukaryotic common ancestor (LECA), gaining capabilities along the way, though the sequence of steps involved has been disputed, and may not have started with symbiogenesis. In turn, the LECA gave rise to the eukaryotes' crown group, containing the ancestors of animals, fungi, plants, and a diverse range of single-celled organisms.

Non-motile bacteria are bacteria species that lack the ability and structures that would allow them to propel themselves, under their own power, through their environment. When non-motile bacteria are cultured in a stab tube, they only grow along the stab line. If the bacteria are mobile, the line will appear diffuse and extend into the medium. The cell structures that provide the ability for locomotion are the cilia and flagella. Coliform and Streptococci are examples of non-motile bacteria as are Klebsiella pneumoniae, and Yersinia pestis. Motility is one characteristic used in the identification of bacteria and evidence of possessing structures: peritrichous flagella, polar flagella and/or a combination of both.

Though the lack of motility might be regarded a disadvantage, some non-motile bacteria possess structures that allow their attachment to eukaryotic cells, like GI mucousal cells.

A planula is the free-swimming, flattened, ciliated, bilaterally symmetric larval form of various cnidarian species and also in some species of Ctenophores, which are not closely related to cnidarians. Some groups of Nemerteans also produce larvae that are very similar to the planula, which are called planuliform larva. In a few cnidarian clades, like Aplanulata and the parasitic Myxozoa, the planula larval stage has been lost.

The cytoskeleton is a complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells, including those of bacteria and archaea. In eukaryotes, it extends from the cell nucleus to the cell membrane and is composed of similar proteins in the various organisms. It is composed of three main components: microfilaments, intermediate filaments, and microtubules, and these are all capable of rapid growth and/or disassembly depending on the cell's requirements.

The cytoskeleton can perform many functions. Its primary function is to give the cell its shape and mechanical resistance to deformation, and through association with extracellular connective tissue and other cells it stabilizes entire tissues. The cytoskeleton can also contract, thereby deforming the cell and the cell's environment and allowing cells to migrate. Moreover, it is involved in many cell signaling pathways and in the uptake of extracellular material (endocytosis), the segregation of chromosomes during cellular division, the cytokinesis stage of cell division, as scaffolding to organize the contents of the cell in space and in intracellular transport (for example, the movement of vesicles and organelles within the cell) and can be a template for the construction of a cell wall. Furthermore, it can form specialized structures, such as flagella, cilia, lamellipodia and podosomes. The structure, function and dynamic behavior of the cytoskeleton can be very different, depending on organism and cell type. Even within one cell, the cytoskeleton can change through association with other proteins and the previous history of the network.

Ostracodermi (lit. 'shell-skins') or ostracoderms is an informal group of vertebrate animals that include all armored jawless fish of the Paleozoic Era. The term does not often appear in classifications today because it is paraphyletic (excluding jawed fishes and possibly the cyclostomes if anaspids are closer to them) and thus does not correspond to one evolutionary lineage. However, the term is still used as an informal way of loosely grouping together the armored jawless fishes.

An innovation of ostracoderms was the use of gills not for feeding, but exclusively for respiration. Earlier chordates with gill precursors used them for both respiration and feeding. Ostracoderms had separate pharyngeal gill pouches along the side of the head, which were permanently open with no protective operculum. Unlike invertebrates that use ciliated motion to move food, ostracoderms used their muscular pharynx to create a suction that pulled small and slow-moving prey into their mouths.

Trichoplax adhaerens is one of the four named species in the phylum Placozoa. The others are Hoilungia hongkongensis, Polyplacotoma mediterranea and Cladtertia collaboinventa. Placozoa is a basal group of multicellular animals, possible relatives of Cnidaria. Trichoplax are very flat organisms commonly less than 4 mm in diameter, lacking any organs or internal structures. They have two cellular layers: the top epitheloid layer is made of ciliated "cover cells" flattened toward the outside of the organism, and the bottom layer is made up of cylinder cells that possess cilia used in locomotion, and gland cells that lack cilia. Between these layers is the fibre syncytium, a liquid-filled cavity strutted open by star-like fibres.

Trichoplax feed by absorbing food particles—mainly microbes—with their underside. They generally reproduce asexually, by dividing or budding, but can also reproduce sexually. Though Trichoplax has a small genome in comparison to other animals, nearly 87% of its 11,514 predicted protein-coding genes are identifiably similar to known genes in other animals.

Nasal hair or nose hair is the hair in the nostril. Adult human noses have hairs, which serve as a crude air filter to stop foreign particles from entering the nasal cavity, as well as to help collect moisture. Nasal hair is different from the cilia of the ciliated lining of the nasal cavity. These cilia are microtubule-based structures that are found in the respiratory tract, involved in the mucociliary clearance mechanism.

The Doliolida are an order of small marine chordates of the subphylum Tunicata. They are in the class Thaliacea, which also includes the salps and pyrosomes. The doliolid body is small, typically 1–2 mm long, and barrel-shaped; it features two wide siphons, one at the front and the other at the back end, and eight or nine circular muscle strands reminiscent of barrel bands.

Like all tunicates, except for the predatory tunicate, they are filter feeders. Unlike the related class Ascidiacea, which are sessile, but like the class Appendicularia, they are free-swimming plankton; cilia pump water through the body which drives them forward. As the water passes through, small particles and plankton on which the animal feeds are strained from the water by the gill slits. Doliolids can also move by contracting the muscular bands around the body creating a temporary water jet that thrusts them forward or backward quite quickly.

In anatomy, a process (Latin: processus) is a projection or outgrowth of tissue from a larger body. For instance, in a vertebra, a process may serve for muscle attachment and leverage (as in the case of the transverse and spinous processes), or to fit (forming a synovial joint), with another vertebra (as in the case of the articular processes). The word is also used at the microanatomic level, where cells can have processes such as cilia or pedicels. Depending on the tissue, processes may also be called by other terms, such as apophysis, tubercle, or protuberance.

The centrosome (Latin centrum 'centre' + Greek sōma 'body') (archaically cytocentre) is a non-membrane bounded organelle in the animal cell that serves as the main microtubule organizing centre (MTOC) and a regulator of cell-cycle progression. The centrosome provides structure for the cell. It is thought to have evolved only in the metazoan lineage of eukaryotic cells. Fungi and plants lack centrosomes and therefore use other structures to organize their microtubules. Although the centrosome has a key role in efficient mitosis in animal cells, it is not essential in certain fly and flatworm species.

In non-rodent mammals the sperm contributes the major part of the centrosome, the centrioles. Centrosomes are composed of two centrioles arranged at right angles to each other, and surrounded by a dense, highly structured mass of proteins termed the pericentriolar material (PCM). The PCM contains proteins responsible for microtubule nucleation and anchoring — including γ-tubulin, pericentrin and ninein. In general, each centriole of the centrosome is based on a nine-triplet microtubule assembled in a cartwheel structure, and contains centrin, cenexin and tektin.In many cell types, the centrosome is replaced by a cilium during cellular differentiation. However, once the cell starts to divide, the cilium is replaced again by the centrosome.

In anatomy, a nasal concha (/ˈkɒnkə/; pl.: conchae; /ˈkɒnkiː/; Latin for 'shell'), also called a nasal turbinate or turbinal, is a long, narrow, curled shelf of bone that protrudes into the breathing passage of the nose in humans and various other animals. The conchae are shaped like an elongated seashell, which gave them their name (Latin concha from Greek κόγχη). A concha is any of the scrolled spongy bones of the nasal passages in vertebrates.

In humans, the conchae divide the nasal airway into four groove-like air passages, and are responsible for forcing inhaled air to flow in a steady, regular pattern around the largest possible surface area of nasal mucosa. As a ciliated mucous membrane with shallow blood supply, the nasal mucosa cleans, humidifies and warms the inhaled air in preparation for the lungs.

Mucociliary clearance (MCC), mucociliary transport, or the mucociliary escalator describes the self-clearing mechanism of the airways in the respiratory system. It is one of the two protective processes for the lungs in removing inhaled particles including pathogens before they can reach the delicate tissue of the lungs. The other clearance mechanism is provided by the cough reflex. Mucociliary clearance has a major role in pulmonary hygiene.

MCC effectiveness relies on the correct properties of the airway surface liquid produced, both of the periciliary sol layer and the overlying mucus gel layer, and of the number and quality of the cilia present in the lining of the airways. An important factor is the rate of mucin secretion. The ion channels CFTR and ENaC work together to maintain the necessary hydration of the airway surface liquid.