Thresher sharks are large lamniform shark

Shark

Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....

s of the family Alopiidae. Found in all temperate and tropical ocean

Ocean

An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...

s of the world, the family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 contains three species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 all within the genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 Alopias.
The genus and family name derive from the Greek

Greek language

Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 word alopex, meaning fox

Fox

Fox is a common name for many species of omnivorous mammals belonging to the Canidae family. Foxes are small to medium-sized canids , characterized by possessing a long narrow snout, and a bushy tail .Members of about 37 species are referred to as foxes, of which only 12 species actually belong to...

. Indeed the long-tailed thresher shark

Long-tailed thresher shark

The common thresher is the largest species of thresher shark, family Alopiidae, attaining a maximum known length of . Almost half of that length consists of the elongated upper lobe of its caudal fin...

, Alopias vulpinus, is named the fox shark by some authorities. The common name is derived from a distinctive thresher

Thresher

Thresher may refer to:*Threshing machine , a device that first separates the head of a stalk of grain from the straw, and then further separates the kernel from the rest of the head...

-like tail or caudal fin which can be as long as the body of the shark itself.
There are three extant thresher shark species, all in the genus Alopias.