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Clavibacter
Clavibacter: genus of Gram-positive coryneform plant-pathogenic bacteria (Microbacteriaceae), established 1984; includes C. michiganensis, tomato bacterial canker agent, and C. nebraskensis, Goss's wilt of maize.
Clavibacter michiganensis
Clavibacter michiganensis (basonym Bacterium michiganense, Smith 1910) is a Gram-positive, seed-borne plant-pathogenic bacterium causing bacterial canker of tomato; formerly split into subspecies, most were raised to species, leaving C. michiganensis as the tomato canker pathogen, an EPPO A2 quarantine-listed pest.
Claviceps purpurea
Claviceps purpurea, the ergot fungus (ergot), an ascomycete in Clavicipitaceae that infects grass ovaries, replaces grain with toxic alkaloid-containing sclerotia, causes ergotism, and splits into four cryptic species.
Clavicle
Clavicle (collarbone): the doubly curved bone linking sternum and scapula, the only bony connection of arm to trunk. Ossifies first among long bones; fractures are ~5% of adult fractures.
Clavija
Clavija Ruiz & Pav. is a Neotropical genus of about 56-60 species of understory shrubs and treelets in Primulaceae (Theophrastoideae), ranging from Nicaragua to southern Brazil, with large leathery leaves, orange flowers, and fleshy fruits.
Clavulanic acid
Clavulanic acid, from Streptomyces clavuligerus, is a β-lactam β-lactamase inhibitor with weak antibacterial activity, used with amoxicillin (Augmentin) and ticarcillin (Timentin) against class A β-lactamase producers.
Clavulina
Clavulina J. Schröt. is a genus of about 52 clavarioid (coral-like) basidiomycete fungi in Cantharellales, Hydnaceae, defined by two-spored stichic basidia; not to be confused with the foraminiferan genus Clavulina d'Orbigny, 1826.
Clavulina cristata
Clavulina cristata, also called Clavulina coralloides or crested coral, is a common white ectomycorrhizal coral fungus of temperate woodland, with crested branch tips, two-spored basidia, and frequent blackening by the parasite Helminthosphaeria clavariarum.
Clavulinaceae
Clavulinaceae Donk (1970), fairy-club fungi, a family in Cantharellales, Basidiomycota, typified by Clavulina; includes Clavulina, Membranomyces, and Multiclavula. Molecular work proposes synonymy with Hydnaceae, though some databases still accept it.
Claw
Claw: the curved keratin sheath on the tip of a digit, built around the distal phalanx; homologous with nails and hooves. Present since the Carboniferous; felids have retractile claws; declawing (onychectomy) amputates the last toe bone and is opposed by major veterinary associations.
Clay Armstrong
Clay Armstrong is an American physiologist and emeritus professor at the University of Pennsylvania who deduced the structure and gating of potassium channels from squid giant axons.
Clay F. Semenkovich
Clay F. Semenkovich is an American endocrinologist who is Chief of Endocrinology, Metabolism, and Lipid Research at Washington University School of Medicine in St. Louis, studying lipid metabolism.
Claytonia
Claytonia (springbeauties) is a genus of about 33 Montiaceae herbs native to temperate Asia and North and Central America, named for botanist John Clayton; includes edible-tubered C. virginica and miner's lettuce C. perfoliata, moved from Portulacaceae by APG III in 2009.
Clazakizumab
Clazakizumab, once codeveloped as BMS-945429, is a humanized monoclonal antibody that blocks interleukin-6; its phase 3 kidney transplant trial failed, and Eli Lilly licensed it in 2026.
Clazosentan
Clazosentan (Pivlaz), a selective endothelin A receptor antagonist by Actelion/Idorsia, approved in Japan (2022) to prevent cerebral vasospasm after aneurysmal subarachnoid hemorrhage surgery; reduces vasospasm but not mortality or functional outcome.
CLCN4-related X-linked intellectual disability syndrome
CLCN4-related X-linked intellectual disability syndrome, also called Raynaud-Claes syndrome (MRXSRC, OMIM 300114), is a rare Xp22.2 chloride/proton exchanger gene disorder causing intellectual disability, epilepsy, and behavioral problems in males and females.
CLDN1
CLDN1 (claudin 1, 3q28) encodes a 211-aa four-transmembrane tight junction protein. It is an HCV entry co-receptor, its loss causes NISCH/ILVASC ichthyosis-sclerosing cholangitis syndrome, and it is a dual tumor promoter/suppressor and antibody-drug target.
CLDN18
CLDN18 (claudin 18, SFTA5/SFTPJ) is a human gene at 3q22.3 encoding a tight-junction claudin with two isoforms: lung-restricted CLDN18.1 and gastric CLDN18.2, a surface-exposed cancer target of zolbetuximab.
CLDN5
CLDN5 (claudin 5, TMVCF) is a human protein-coding gene at 22q11.21 encoding the dominant endothelial tight junction protein of the blood-brain barrier, deleted in 22q11 deletion syndromes and a drug-delivery target.
CLDN7
CLDN7 (claudin 7, CEPTRL2) is a human gene on chromosome 17p13.1 encoding a 211-amino-acid, four-transmembrane tight junction protein expressed in kidney collecting duct, intestine, and airway epithelia, regulating paracellular chloride permeability, EpCAM-dependent basolateral localization, and showing bidirectional prognostic roles in cancer.
Clean-up crew (reef aquarium)
Clean-up crew (CUC), reef aquarium team of snails, hermit crabs, shrimp, and urchins that grazes algae and scavenges detritus. Modern stocking is about one grazing snail per 5 gallons, added after cycling, not one per gallon.
Cleaner shrimp
Cleaner shrimp, marine decapods such as Lysmata amboinensis (scarlet or skunk cleaner shrimp), remove parasites from reef fish at cleaning stations; 51 shrimp species clean, and they serve as aquaculture biocontrols.
Cleaning
Cleaning: removal of soil, dirt, and germs from surfaces using water, soap, and scrubbing; distinct from sanitizing and disinfecting, which it should precede.
Cleanliness
Cleanliness is freedom from dirt and disease-causing microbes; hygiene is the practices reducing pathogen transmission. Covers handwashing mechanisms, 1.4 million WASH-preventable deaths, JMP hygiene ladders, ritual purity traditions, and 2025 WHO guidelines.
Clear aligners
Clear aligners are removable clear plastic orthodontic trays, including Invisalign, worn about 22 hours daily to treat mild-to-moderate malocclusion; less effective than braces for complex movements.
Clear cell adenocarcinoma of the ovary
Clear cell adenocarcinoma of the ovary (ovarian clear cell carcinoma, OCCC, ORPHA:398971) is a rare epithelial ovarian cancer, ~10% of EOC, linked to endometriosis, ARID1A/PIK3CA mutations, good early-stage prognosis, and platinum-resistant advanced disease.
Clear cell renal carcinoma
Clear cell renal cell carcinoma (ccRCC, conventional renal cell carcinoma) is the most common kidney cancer in adults, 70–80% of RCC, defined by clear lipid- and glycogen-rich cytoplasm and VHL/HIF pathway loss, with worse prognosis than papillary or chromophobe subtypes.
Clear cell sarcoma of kidney
Clear cell sarcoma of kidney (CCSK) is a rare childhood renal cancer, second most common after Wilms tumor, BCOR ITD-driven, metastasizing to bone and brain, treated with surgery, chemotherapy, and radiation.
CLEAR trial
CLEAR (Study 307, NCT02811861): phase 3 trial of lenvatinib plus pembrolizumab or everolimus versus sunitinib in first-line advanced renal cell carcinoma; distinct from CLEAR Outcomes.
Clearcutting
Clearcutting is an even-aged forestry method that removes essentially all trees in a stand in a single cut, common since 18th-century Germany and favored for shade-intolerant species like aspen.