#agenesis

• Abrachia — An extremely rare congenital malformation characterized by the complete absence or rudimentary development of the arms (upper limbs) in a fetus or developing organism; a severe anatomical anomaly within the category of limb agenesis, similar to or closely related to amelia and congenital abrachia.
• Abrachiocephalus — A teratological monster, fetus, or organism with severe congenital malformations, characterized by the simultaneous absence of both arms and the head, or by the abnormal and rudimentary fusion of cephalic structures in the complete absence of upper limbs; (adjectival) presenting the anatomical features of this embryonic developmental anomaly.
• Abrachiocephaly — A complex and extremely severe congenital malformation characterized by the simultaneous absence of both the head (acephalia) and both upper limbs (abrachia) in a fetus or developing organism; an early embryonic developmental anomaly, incompatible with life, studied within classical and experimental teratology.
• Agamobium — An organism or generation that is part of an alternation of generations cycle (metagenesis) and reproduces exclusively asexually. Structurally, the agamobium represents the alternating phase that subsequently gives rise to a sexual generation (gamobium), thereby ensuring genetic diversity and the survival of lower invertebrate or parasite species in variable environments.
• Agenetic — Relating to agenesis; characterized by the congenital absence of an organ, tissue, or body part, caused by the failure of its development during embryonic life. In a clinical sense, it describes an organism, anatomical segment, or process affected by this severe structural development anomaly.
• Agenesis — The congenital absence of an organ, tissue, or body part, caused by the failure of its development during embryonic life. Unlike aplasia, where the embryonic bud exists but fails to fully mature, in this severe structural anomaly the initial blueprint of the organ is completely missing from the genetic profile.
• Agenitalism — An extremely rare clinical condition characterized by the total congenital absence of internal and external genital organs or by the complete lack of hormonal secretion from the gonads (severe sexual infantilism). This endocrine and organic structural disorder profoundly affects the development of secondary sexual characteristics and reproductive capacity.
• Agenesis — A rare congenital malformation characterized by the complete absence, structural underdeveloped state, or congenital lack of an organ, tissue, or body part since the intrauterine development period. The phenomenon is caused by genetic errors or teratogenic factors manifesting during the early phases of organogenesis.
• Aleurolite — A consolidated detrital sedimentary rock formed through the cementation and diagenesis of aleurite (fine mineral dust, chiefly quartzous). The dimensions of its component grains are intermediate between those of sandstones and argillites, ranging from 0.002 to 0.06 millimeters. It often exhibits fine stratification and is used in geology to reconstruct ancient fossil or lacustrine sedimentary environments.
• Amyelia — An extremely rare and severe congenital malformation within the neural tube defects spectrum, characterized by the total absence or complete developmental arrest of the spinal cord. This severe structural anomaly occurs during the first weeks of embryogenesis due to the failure of the posterior neuropore to close, being incompatible with extrauterine life and often associated with other major cranial malformations.
• Anadiagenesis — An intermediate or deep stage within the general process of diagenesis, characterized by intense structural physicochemical transformations of sediments buried at great depths under increased temperatures and pressures, without reaching metamorphism. This phenomenon involves the recrystallization of clay minerals, massive compaction, deep dehydration, and cementation of interstitial fluids, leading to the definitive lithification of sedimentary rocks.
• Anagenesis — A macroevolutionary mechanism or process characterized by the linear and progressive evolution of a single phyletic lineage, wherein an entire species undergoes structural and genetic transformations accumulated over time, gradually transforming into a new species without branching. This evolutionary phenomenon, opposite to cladogenesis, involves the complete replacement of the old gene pool through continuous adaptation to the environment, leading to the emergence of superior morphological and physiological traits.
• Anchimetamorphism — A geological process of incipient, very low-grade metamorphism that marks the transition between diagenesis (sediment consolidation) and regional metamorphism proper (greenschist facies); it occurs at relatively low temperatures and pressures, causing partial recrystallization of clay minerals without completely destroying the original sedimentary structures.
• Anepiphysia — An extremely rare congenital malformation or embryonic developmental structural anomaly characterized by the partial or total absence of the pineal gland (epiphysis cerebri). Functionally, this severe bio-structural condition profoundly disrupts the endocrine secretion of melatonin, directly impacting the circadian rhythm, sleep-wake cycles, and neuroendocrine mechanisms of sexual maturation.
• Aneresis — A rare congenital malformation or structural anomaly characterized by the partial or total absence of the anus, often associated with anal imperforation or the presence of abnormal rectal fistulas. Clinically and functionally, this severe bio-structural condition blocks the normal evacuation of fecal matter in the newborn, requiring emergency reconstructive surgical intervention immediately after birth.
• Anodontia — A rare congenital anomaly characterized by the total or partial absence of teeth, caused by the lack of tooth bud formation within the jawbones during intrauterine development. This structural defect affects both deciduous (baby) and permanent dentitions, causing severe disturbances in mastication, speech, and aesthetics, requiring complex prosthetic treatment.
• Apneumia — An extremely rare congenital malformation characterized by the complete, structural, and anatomical absence of one or both lungs, resulting from an early developmental arrest of the respiratory bud during the embryonic stage. This severe anomaly is investigated within fetal pathology and is typically associated with other major systemic defects.
• Argillite — A compact argillaceous sedimentary rock, structurally formed through the diagenesis and deep cementation of clay muds, characterized by a higher hardness than simple clay and by the absence of fissility or the ability to split into thin sheets (unlike clay shales). In a geological sense, argillite represents an intermediate stage of metamorphism between soft pelitic sedimentary rocks and crystalline clay shales.
• Aromorphosis — A primary direction or mechanism in the progressive evolution of living systems (introduced by Alexey Severtsov) consisting of the acquisition of major, complex morphophysiological changes that raise the general level of organismal organization.
• Authigenic — Said of minerals or sedimentary components that formed directly in situ, within the sediment or host rock, through processes of chemical precipitation, recrystallization, or diagenetic transformation, rather than being transported from elsewhere as pre-existing detrital material.