#spine

• Acanthiferous — An anatomical and zoological term used to describe an organism, organ, or anatomical structure that is covered with spines, thorns, or sharp rigid formations, or that bears such defensive elements. In taxonomy and paleontology, this adjective serves as an essential morphological criterion for describing and classifying certain marine invertebrate species (such as radiolarians or some bryozoans) or fossil reptiles whose exoskeletons or shells are equipped with spiny extensions.
• Acanthophilous — A plant morphological term used as an adjective to describe a plant displaying a strong ecological affinity for environments populated by spiny species, or whose leaves have partially or completely transformed into spines or thorns (a typical adaptation to drought). As a masculine noun, it defines a foliar anatomical structure evolutionarily modified into a sharp, rigid needle (as seen in cactus leaves or certain acacia species), serving to reduce water loss via transpiration and ensure self-defense.
• Acanthophorous — A scholarly morphological term used as an adjective to describe an organism, organ, or anatomical structure equipped with spine-bearing elements, thorns, or sharp rigid protrusions. As a masculine noun, it defines a skeletal part, an appendage, or a specialized cuticular zone that supports or bears a defensive spine (frequently encountered in the exoskeleton structure of some marine crustaceans, bryozoans, or fossil fishes from the Paleozoic era).
• Acanthology — A specialized branch or treatise within the biological sciences (botany and zoology) that deals with the systematic study, classification, anatomical structure, and ecological role of spines, thorns, prickles, or sharp rigid formations present in plants and animals. The term governs research focused on the defensive and adaptive morphological modifications of xerophytic organisms or invertebrates and vertebrates armed with spikes.
• Acrocomia — A genus of monocotyledonous plants in the palm family (Arecaceae), native to tropical and subtropical regions of Central and South America. These palms are characterized by massive trunks covered with sharp spines and dense crowns of pinnate leaves.
• Acromion — A flattened and broadened bony projection forming the superior extremity of the scapular spine, articulating directly with the clavicle and representing the highest structural point of the shoulder skeleton.
• Sacrum — An obsolete, rare graphic variant or faulty transcription for the sacrum bone (os sacrum); the large triangular bony piece located at the base of the vertebral column, formed by the structural fusion of the five sacral vertebrae, articulating laterally with the iliac bones to close the pelvic girdle.
• Actinacanth — A zoological term used to describe an organism, an anatomical structure, or a skeletal element provided with spines, spicules, or sharp extensions arranged in a radiating manner. In the context of paleontology and aquatic taxonomy, it specifically describes the morphology of certain radiolarians, sponges, or ancient marine fauna whose rigid support elements emerge from a common center in the shape of stinging rays.
• Ancistrocactus — A genus of succulent plants in the family Cactaceae, native to the arid and semi-desert regions of the southern United States (Texas) and northern Mexico. It comprises relatively small, globular to cylindrical cacti with well-defined ribs and areoles bearing strong central spines, at least one of which is long and sharply hooked, a morphological feature that gives the genus its name.
• Ancistrocactus brevihamatus — A species of cactus endemic to the arid regions of Texas and northern Mexico, characterized by small globular or cylindrical stems, pronounced ribs, and strong central spines heavily hooked like a fishhook. The plant exhibits extreme adaptation to deep drought and develops bell-shaped flowers of greenish-yellow, pink, or reddish-brown color, highly valued in succulent collections for its spectacular defensive morphology.
• Anoplous — Lacking natural weapons, such as thorns, spines, horns, spurs, stings, or sharp mandibles; an organism, insect, or anatomical structure that is defensively vulnerable but structurally adapted for parasitic or passive lifestyles. In taxonomy, the term often describes species or genera characterized by a smooth, outwardly harmless morphology but structurally equipped with alternative survival or attachment mechanisms.
• Hedgehog — A small insectivorous mammal (Erinaceus europaeus) with a pointed snout and its back covered with long, rigid spines, which rolls into a ball when endangered as a structural self-defense mechanism. In a technical or military sense, the term denotes a defensive obstacle made of crossed beams (Czech hedgehog) used as an anti-tank barrier, an industrial part equipped with protruding teeth, or a stiff cylindrical brush used for cleaning chimneys.
• Astrophytum asterias — An endemic species of small succulent plants within the Astrophytum genus (Cactaceae family), with a globose, flattened stem completely lacking spines, typically divided into exactly 8 flat, regular ribs. Its greenish-grey surface is decorated with numerous trichomes (microscopic white dots made of tiny hairs), featuring large, woolly areoles in the center from which yellow flowers with a red-orange center emerge; it is a protected species, endangered in its native habitat of Mexico and Texas.
• Astrophytum capricorne — A species of xerophytic plants within the Astrophytum genus (Cactaceae family), native to the semi-desert regions of Mexico (Chihuahuan Desert), characterized by a spherical stem that becomes cylindrical at maturity, divided into 7-8 sharp ribs. The species is distinguished by its long, flexible, flattened, and twisted spines reminiscent of a goat's horns (or a capricorn's), and by its large, yellow flowers with a deep purple or red center.
• Astrophytum myriostigma — A species of succulent cacti within the Astrophytum genus (Cactaceae family), native to the mountainous and arid regions of central and northern Mexico. The plant has a globose stem completely lacking spines, typically divided into 5 prominent ribs, giving it a three-dimensional star shape; its entire epidermis is densely covered by thousands of trichomes (microscopic white dots), giving it a characteristic silver-white hue, and its large flowers are pure yellow without a red center.
• Axis vertebra — The second cervical vertebra of the spine in humans and higher animals, situated directly below the atlas, serving the structural role of a pivot for the delicate rotation of the head. The bony piece is characterized by a vertical process called the odontoid process, around which cranial torsional movements are executed. In zoology, the term also designates a species of deer native to India (Cervus axis), characterized by a spotted coat and slender antlers.
• Aylostera spinosissima — A perennial species of dwarf cactus native to the mountainous and arid regions of Bolivia, structurally recognized by its dark green globose or short cylindrical stems, characterized by an amazing density of long, thin, and extremely rigid spines. Its specific epithet originates from Latin, meaning 'most thorny', reflecting this dense protective shield from which spectacular, deep brick-red funnel-shaped flowers erupt delicately in spring from the lower areoles.