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The branch of applied physics which deals with the motion of projectiles and the conditions governing their motion. Ballistics is, for practical purposes, subdivided into exterior and interior ballistics. Exterior ballistics begins at the instant a…

The common name for any of the perciform fishes belonging to a single genus, Sphyraena, in the family Sphyraenidae. Barracudas are characterized by an elongate, slightly compressed body; a long, pointed head; a large horizontal mouth with…

An order (or superorder) of the gastropod molluscan subclass Pulmonata containing about 2500 species that are grouped into 11–15 families. Only a few members of the family Ellobiidae are terrestrial, with the other species today being tidal to…

A common name applying to a large group of fishes, mostly in the order Perciformes, generally having the following characteristics: body about 2.5–3 times longer than its depth; two dorsal fins, with the first composed of stiff spines; pectoral fins…

An order of freshwater crustaceans (superorder Syncarida) whose members lack a carapace and whose head and thorax are not fused. All the thoracic appendages of bathynellaceans are biramous and similar. The sixth pleomere is fused to the telson,…

An elasmobranch subdivision of cartilaginous fishes known collectively as the rays, skates, or batoids. Batoidea is one of the two subdivisions of the subclass Elasmobranchii (class Chondrichthyes) and consists of 4 extant orders, 17–20 families,…

An order of actinopterygian (ray-finned) fishes consisting of a single family, Batrachoididae, collectively known as the toadfishes. The order Batrachoidiformes comprises a single family (Batrachoididae), four subfamilies, 23 genera, and…

A class of the phylum Rotifera characterized by paired gonads and obligately asexual reproduction, found in diverse freshwater habitats worldwide. Bdelloid rotifers are among the most common microinvertebrates, particularly in ephemerally aquatic…

The bear family (Ursidae) contains the largest terrestrial carnivores. Most taxonomists agree that there are eight extant species of bears in three subfamilies: Ursinae (American black, Asiatic black, brown, polar, Malayan Sun, and sloth bears);…

The common name for the most primitive living rodent. The beaver has an ancestry that goes back to the time when modern mammals evolved. Two families and three species of beavers exist in the world. The family Aplodontidae contains a single species:…

The management and maintenance of colonies of honeybees for human purposes. Beekeeping is an ancient art. Although the commonly known honeybee species (Fig. 1) is native to Europe and Africa, humans have transported them to other continents. The…

An order of extinct 10-armed cephalopod mollusks with an internal shell. The order Belemnitida belongs to the subclass Coleoidea in the class Cephalopoda (phylum Mollusca). Constituent members, which are all extinct, are known as belemnites (Fig. 1)…

An order of actinopterygian (ray-finned) fishes containing the flyingfishes, needlefishes, and halfbeaks. Fishes in the order Beloniformes, along with those of the Atheriniformes and Cyprinodontiformes, comprise the series Atherinomorpha. Members of…

An order of the phylum Ctenophora (comb jellies) comprising two genera, Beroë and Neis. The single species of Neis (N. cordigera) is known only from Australia, but many species of Beroë have been described from polar to tropical waters all over the…

An order of somewhat intermediate position among actinopterygian (ray-finned) fishes. Members of the order Beryciformes share the following features with the perciform fishes: fin spines, ctenoid scales, an upper jaw bordered by the premaxillae, a…

An order of Zoomastigophorea (Protozoa). They are colorless, free-living cells, each with two flagella, one of which is used for attaching the organism to its exoskeleton (lorica). Although the attachment is normally from the front end, the…

Marine sponges that are able to erode calcareous substrates such as coral, mollusk shells, and limestone, also called boring or excavating sponges. Confirmed eroders belong to the families Samidae, Thoosidae, Clionaidae, Spirastrellidae, Acarnidae,…

The name for two species (genus Bison) of the cattle family Bovidae in the mammalian order Artiodactyla found in North America and Europe. The North American bison (Bison bison; see illustration) is often called buffalo, but should not be confused…

An extinct group of epifaunal bivalves that constructed reefs during the late Mesozoic. The valves of rudists are coiled to cylindrical in external form, and the shapes and sizes of rudist shells are extreme relative to other members of the class…

One of the seven existing classes in the phylum Mollusca; sometimes known as Pelecypoda. All members of the Bivalvia (bivalves) are aquatic, living at all depths of the sea and in brackish waters and freshwaters. With about 25,000 living species…

A class of extinct Pelmatozoa in the subphylum Blastozoa which arose in the Ordovician and flourished in the Carboniferous and Permian. Blastoids did not survive the Permo-Triassic mass extinction event. Historically, two orders of the Blastoidea…

A taxonomic order of insects comprising the cockroaches and termites. The order Blattodea, also referred to as Blattaria, contains at least 4500 species of cockroaches (Fig. 1) and 3000 species of termites. Previously, termites were assigned to a…

A predatory and voracious species of fish in the order Perciformes that ranges throughout the tropical and temperate seas of the world, except for the eastern and central Pacific areas. A single species, Pomatomus saltatrix (see illustration), makes…

A variety of marine bivalve mollusks which penetrate solid substrata. They represent seven families and vary in the extent to which they are specialized, in the type of substrata they utilize, and in their method of boring. It is difficult to…

A phylum of solitary, exclusively marine, coelomate, bivalved animals, with both valves symmetrical about a median longitudinal plane. Brachiopods are typically attached to the substrate by a posteriorly located cuticle-covered stalk called a…

An order of freshwater, obligate, ectosymbiotic clitellate annelids known as the crayfish worms. Branchiobdellidans form a monophyletic group within a larger clade including the Acanthobdellida and Hirudinida; the Lumbriculida constitute their…

A class of crustaceans. Formerly, four extant orders were recognized: Anostraca, Notostraca, Conchostraca, and Cladocera, the first two of which are well defined. The Conchostraca consist of two groups which, although superficially similar, differ…

A subclass of the Crustacea known as the fish lice. They are ectoparasites of freshwater and marine fish on such areas as the base of fins and the gill chamber walls. Argulus (see illustration) is a common genus. They are a small homogeneous group,…

An order of exclusively deep-sea asteroids (sea stars or starfish) possessing an unusual body form adapted for suspension feeding. These adaptations in the Brisingida (also called brisingids or brisingidans) include having 6–20 elongate arms (there…

A phylum of sessile aquatic invertebrates (also called Polyzoa) that form colonies of zooids. Each zooid, in its basic form, has a lophophore of ciliated tentacles situated distally on an introvert, a looped gut with the mouth inside the lophophore…

The name for several members of the family Bovidae in the mammalian order Artiodactyla. The buffalo is an Old World species that resembles the oxen in general appearance. The North American bison is often called a buffalo, but it is not related to…

Terrestrial and aquatic animals that are capable of excavating holes in the ground for protection from adverse environmental conditions, as well as for storing food. Burrowing animals are uniquely adapted species, having the capacity to dig burrows…

One of five main groups of gastropods (snails) in the phylum Mollusca (snails, clams, squids, and their relatives). With approximately 190 families in 29 superfamilies (see table), caenogastropods form a large, mostly marine group, including about…

An order of Copepoda that includes the larger and more abundant of the pelagic species. Some authorities consider the Calanoida an order of the subclass Copepoda. In the food cycles of the sea these copepods are the most important group of marine…

A class of the phylum Porifera, including exclusively marine sponges with a skeleton composed of spicules of calcium carbonate to which can be added a solid basal calcitic skeleton. The sponges that constitute the phylum Porifera are assigned to…

The name given to two species of mammals that are members of the family Camelidae in the order Artiodactyla. The two camel species are the Bactrian camel (Camelus bactrianus) and the Arabian or dromedary camel (C. dromedarius). Both species are…

An extinct subclass of stalked Crinoidea; a class of the phylum Echinodermata. The Camerata include more than 235 genera confined to the Paleozoic Era, ranging from the Early Ordovician to the Late Permian. Camerate crinoids were one of the four…

A small class of primitive echinoderms (subphylum Echinozoa) known from the single species Camptostroma roddyi based on about 200 specimens from the Early Cambrian (Bonnia-Olenellus Zone) in southeastern Pennsylvania. Camptostroma was originally…

An order of crepuscular (active during predawn or twilight hours) or mainly nocturnal birds collectively known as the nightjars or goatsuckers. Members of the order Caprimulgiformes are apparently most closely related to the owls (Strigiformes).…

A ruminant, Rangifer tarandus, of the deer family, Cervidae. Caribou inhabit the Arctic region and have a circumpolar distribution. In Europe, caribou are called reindeer; in North America (Alaska and Canada), only the domestic forms are called…

The common name for a number of freshwater cypriniform fishes of the family Cyprinidae. The carp originated in China, where for centuries it was raised for food. It was imported into the United States from Europe, where it also has been raised for…

The name originally given by C. Claus in 1880 to what is now recognized as an unnatural (nonmonophyletic) group of echinoids (sea urchins) containing the lamp urchins. There are only about 30 extant species of cassiduloids (that is, members of the…

The common name used to describe any member of the carnivoran mammalian family Felidae. Members of the family Felidae (order Carnivora, class Mammalia) are known as cats. Typically, in common usage, the term is restricted to the domestic cat and…

A small group of turbellarian worms, constituting one of the two major groups of the phylum Platyhelminthes. The Catenulida comprises about 100 species, whereas the Rhabditophora, the other major group of the Platyhelminthes, comprises thousands of…

Rodents making up the family Caviidae, which includes the guinea pig, rock cavies, mountain cavies, capybara, salt-desert cavy, and mara. All members of the group are indigenous to South America, and the group comprises 15 species in six genera.…

An order of the Heliozoia. There is a central cell mass from which thin stiff arms radiate. The arms are supported internally by arrays of microtubules which terminate internally on a central granule, the centroplast, and the nucleus has an…

An order of marine gastropods assigned to the informal group Opisthobranchia (phylum Mollusca) and often referred to as head-shield sea slugs or bubble shells. The name Cephalaspidea was introduced in 1887 by the French naturalist Paul Henri…

The subclass of Agnatha that includes the jawless vertebrates with a single median nostril, as opposed to the subclass Pteraspidomorpha, in which there are paired nostrils. The Cephalaspidomorpha includes the orders Osteostraci, Galeaspida,…

One of two orders in the subclass Pentastomida of the phylum Arthropoda. The order Cephalobaenida includes primitive pentastomids with six-legged larvae. The hooks are simple, lacking a fulcrum, and disposed in trapeziform pattern, with the anterior…

A group of tiny marine crustaceans (body length 2.0–4.0 mm or 0.08–0.16 in.), discovered in 1954. Initially, cephalocarids were thought to be a living representation of what the primordial crustacean looked like. In recent years, that view has…