Spine (zoology) in the context of "Holocephali"

Sea urchins or urchins (/ˈɜːrtʃɪnz/) are echinoderms in the class Echinoidea. About 950 species live on the seabed, inhabiting all oceans and depth zones from the intertidal zone to deep seas of 5,000 m (16,000 ft). They typically have a globular body covered by a spiny protective tests (hard shells), typically from 3 to 10 cm (1 to 4 in) across. Sea urchins move slowly, crawling with their tube feet, and sometimes pushing themselves with their spines. They feed primarily on algae but also eat slow-moving or sessile animals such as crinoids and sponges. Their predators include sharks, sea otters, starfish, wolf eels, and triggerfish. When unchecked by predators, urchins can create urchin barrens, damaged environments devoid of large algae and the animals associated with them.

Like all echinoderms, adult sea urchins have pentagonal symmetry with their pluteus larvae featuring bilateral (mirror) symmetry; The latter indicates that they belong to the Bilateria, along with chordates, arthropods, annelids and molluscs. Sea urchins are found in every ocean and in every climate, from the tropics to the polar regions, and inhabit marine benthic (sea bed) habitats, from rocky shores to hadal zone depths. The fossil record of the echinoids dates from the Ordovician period, some 450 million years ago. The closest echinoderm relatives of the sea urchin are the sea cucumbers (Holothuroidea), which like them are deuterostomes, a clade that includes the chordates. (Sand dollars are a separate order in the sea urchin class Echinoidea.)

Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and lift, which help the fish swim. Apart from the tail or caudal fin, fish fins have no direct articulations with the axial skeleton and are attached to the core only via muscles and ligaments.

Fish fins are distinctive anatomical features with varying internal structures among different clades: in ray-finned fish (Actinopterygii), fins are mainly composed of spreading bony spines or "rays" covered by a thin stretch of scaleless skin, resembling a folding fan; in lobe-finned fish (Sarcopterygii) such as coelacanths and lungfish, fins are short rays based around a muscular central bud internally supported by a jointed appendicular skeleton; in cartilaginous fish (Chondrichthyes) and jawless fish (Agnatha), fins are fleshy "flippers" supported by a cartilaginous skeleton. The limbs of tetrapods, a mostly terrestrial clade evolved from freshwater lobe-finned fish, are homologous to the pectoral and pelvic fins of all jawed fish.

Porcupines are large rodents with coats of sharp spines, or quills, that protect them against predators. The term covers two families of animals: the Old World porcupines in the family Hystricidae, and the New World porcupines in the family Erethizontidae. Both families display superficially similar coats of rigid or semi-rigid quills, which are modified hairs composed of keratin, and belong to the infraorder Hystricognathi within the diverse order Rodentia. The two groups are distinct and are not closely related to each other within Hystricognathi. The largest species of porcupine is the third-largest living rodent in the world, after the capybara and beaver.

The Old World porcupines (Hystricidae) live in Italy, West and South Asia, and most of Africa. They are large, terrestrial, and strictly nocturnal. New World porcupines (Erethizontidae) are indigenous to North America and northern South America. They live in wooded areas and can climb trees, where some species spend their entire lives. They are generally smaller than their Old World counterparts and are less strictly nocturnal.

Actinopterygii (/ˌæktɪnɒptəˈrɪdʒiaɪ/ ; from Ancient Greek ἀκτίς (aktís) 'ray, beam' and πτέρυξ (ptérux) 'wing, fins'), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that constitute nearly 99% of the over 30,000 living species of fish. The vast majority of extant actinopterygian species are teleosts, and by species count they dominate the subphylum Vertebrata, comprising over 50% of all living vertebrates. They are the most abundant nektonic aquatic animals and are ubiquitous throughout freshwater, brackish and marine environments from the deep sea to subterranean waters to the highest mountain streams. Extant species can range in size from Paedocypris, at 8 mm (0.3 in), to the giant sunfish, at 2,700 kg (6,000 lb), and the giant oarfish, at 8 m (26 ft) (or possibly 11 m (36 ft)). The largest ever known ray-finned fish, the extinct Leedsichthys from the Jurassic, is estimated to have grown to 16.5 m (54 ft).

Ray-finned fish are so called because of their lightly built fins made of webbings of skin supported by radially extended thin bony spines called lepidotrichia, as opposed to the bulkier, fleshy fins of the sister clade Sarcopterygii (lobe-finned fish). Resembling folding fans, the actinopterygian fins can easily change shape, orientation and wetted area, providing superior thrust-to-weight ratios per movement compared to sarcopterygian and chondrichthyian fins. The fin rays attach directly to the proximal or basal skeletal elements, the radials, which represent the articulation between these fins and the internal skeleton (e.g., pelvic and pectoral girdles).

A splinter (also known as a sliver) is a fragment of a larger object, or a foreign body that penetrates or is purposely injected into a body. The foreign body must be lodged inside tissue to be considered a splinter. Splinters may cause initial pain through ripping of flesh and muscle, or infection through bacteria on the foreign object.

Splinters are primarily made of wood, but there are many other types, for example, other common types of splinters are, hair, glass, plastic, metal, and spines of animals.

Quillwork is a form of textile embellishment traditionally practiced by Indigenous peoples of North America that employs the quills of porcupines as an aesthetic element. Quills from bird feathers were also occasionally used in quillwork.

Doliodus is a genus of cartilaginous fish known from the Early Devonian period of what is now New Brunswick, Canada. It includes a single named species, either D. problematicus or D. latispinosus, which was originally described based on isolated teeth and potentially fin spines, but has since had a well-preserved body fossil assigned. The classification of the genus is uncertain, but it has been considered a member of the order Omalodontiformes. A more complete specimen that some authors assign to the genus shows features that are transitional between the extinct acanthodians and cartilaginous fish.