The letter ‘X’ is one of the least common starting letters in the English language, and this scarcity is reflected in animal nomenclature. The few species whose common names begin with ‘X’ stand out precisely because of their unusual initial letter. This rarity is a product of linguistic history and taxonomic tradition, but the animals that do bear the ‘X’ designation are geographically diverse and exhibit unique biological features. Our exploration focuses on these notable exceptions, detailing the animals whose common names begin with this elusive letter and investigating the scientific prefixes that expand the list.
The Most Recognized Animals Starting with X
The African Ground Squirrel, classified within the genus Xerus, is one of the most prominent mammals whose common name begins with ‘X’. These diurnal rodents inhabit the arid savannas and grasslands of Sub-Saharan Africa, living in extensive burrow systems. They use their large, bushy tails as sunshades to reduce heat absorption while foraging. The genus Xerus includes several species, such as the Cape ground squirrel (Xerus inauris) and the unstriped ground squirrel (Xerus rutilus), which feed on seeds, roots, and insects.
The X-ray Tetra (Pristella maxillaris) is a small, freshwater fish native to the Amazon and coastal river systems of South America. This species earns its common name from its translucent body, which allows a faint view of its internal skeleton and organs. The X-ray Tetra is a peaceful, schooling fish, growing to less than two inches long, and is a popular choice in home aquariums.
The Xantus’s Murrelet (Synthliboramphus hypoleucus) is a small, pelagic auk that breeds on islands off the coast of California and Baja California. This bird spends most of its life far out at sea, only coming ashore at night to nest in rock crevices or under dense vegetation. Its name honors the Hungarian zoologist John Xantus de Vesey, demonstrating that some ‘X’ names are derived from the proper names of their discoverers.
Animals Defined by X-Prefixes
Many animals starting with ‘X’ in their scientific name are named after Greek prefixes that describe a particular characteristic. The African Clawed Frog, belonging to the genus Xenopus, is a prime example. Its name is derived from the Greek words xenos (strange) and pous (foot), meaning “strange foot,” a reference to the three small, black claws on each of its hind feet. Xenopus laevis is a fully aquatic species native to Sub-Saharan Africa and is widely studied as a model organism.
The genus Xenops is another group of animals whose name comes from the xeno- prefix, comprising several species of small Neotropical birds. These ovenbirds, such as the Streaked Xenops (Xenops rutilans), are found in Central and South American forests. They forage for insects by moving vertically along tree trunks and branches. Their wedge-shaped bills are adapted for chiseling into wood and prying back bark to access wood-boring larvae.
Other prefixes are also at play, such as Xantho-, meaning yellow, which appears in names like the Xanthic Sargo fish. The term Xylophagous, meaning wood-eating, is used to describe various beetles and insects, such as carpenter bees in the genus Xylocopa, which bore into timber. This reliance on Greek roots often introduces the letter ‘X’ where it would not naturally occur in common English names.
Why X is Rare in Animal Nomenclature
The scarcity of animals whose common names begin with ‘X’ is largely due to the linguistic history of scientific naming. The Linnaean system of binomial nomenclature, which uses Latin and Greek roots, often places ‘X’ in the middle of a word rather than at the beginning. In classical Greek, the letter ‘X’ often represented a sound similar to ‘ks,’ which is not a common initial sound in many languages. When ‘X’ is used at the start of a word, it often results from a transliteration of a foreign name or an obscure Greek root. The sound represented by ‘X’ is frequently replaced by ‘Z’ or ‘S’ in vernacular English, which further limits its appearance in widely recognized common names.