The telson () is the hindmost division of the body of an

arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

. Depending on the definition, the telson is either considered to be the final segment of the arthropod body, or an additional division that is not a true segment on account of not arising in the embryo from teloblast areas as other segments. It never carries any

appendage An appendage (or outgrowth) is an external body part or natural prolongation that protrudes from an organism's body such as an arm or a leg. Protrusions from single-celled bacteria and archaea are known as cell-surface appendages or surface app ...

s, but a forked "tail" called the caudal furca may be present. The shape and composition of the telson differs between arthropod groups.

Crustaceans

lobster Lobsters are Malacostraca, malacostracans Decapoda, decapod crustaceans of the family (biology), family Nephropidae or its Synonym (taxonomy), synonym Homaridae. They have long bodies with muscular tails and live in crevices or burrows on th ...

shrimp A shrimp (: shrimp (American English, US) or shrimps (British English, UK)) is a crustacean with an elongated body and a primarily Aquatic locomotion, swimming mode of locomotion – typically Decapods belonging to the Caridea or Dendrobranchi ...

and other

decapods The Decapoda or decapods, from Ancient Greek δεκάς (''dekás''), meaning "ten", and πούς (''poús''), meaning "foot", is a large order (biology), order of crustaceans within the class Malacostraca, and includes crabs, lobsters, crayfis ...

, the telson, along with the

uropod Uropods are posterior appendages found on a wide variety of crustaceans. They typically have functions in locomotion. Definition Uropods are often defined as the appendages of the last body segment of a crustacean. An alternative definition sugge ...

s, forms the tail fan. This is used as a paddle in the

caridoid escape reaction The caridoid escape reaction, also known as lobstering or tail-flipping, is an innate escape behavior in marine and freshwater eucarid crustaceans such as lobsters, krill, shrimp and crayfish. The reaction, most extensively researched in ...

("lobstering"), whereby an alarmed animal rapidly flexes its tail, causing it to dart backwards.

Krill Krill ''(Euphausiids)'' (: krill) are small and exclusively marine crustaceans of the order (biology), order Euphausiacea, found in all of the world's oceans. The name "krill" comes from the Norwegian language, Norwegian word ', meaning "small ...

can reach speeds of over 60 cm per second by this means. The

trigger Trigger may refer to: Arts, entertainment and media Fictional entities * Trigger (''Only Fools and Horses''), in the TV sitcom * Trigger Argee, in science fiction short stories by James H. Schmitz * Devil Trigger, a transformation ability of ...

time to optical stimulus is, in spite of the low temperatures, only 55

milliseconds A millisecond (from '' milli-'' and second; symbol: ms) is a unit of time in the International System of Units equal to one thousandth (0.001 or 10−3 or 1/1000) of a second or 1000 microseconds. A millisecond is to one second, as one second i ...

. In the

Isopoda Isopoda is an order of crustaceans. Members of this group are called isopods and include both aquatic species and terrestrial species such as woodlice. All have rigid, segmented exoskeletons, two pairs of antennae, seven pairs of jointed l ...

and

Tanaidacea The crustacean order Tanaidacea (known as tanaids) make up a minor group within the class (biology), class Malacostraca. There are about 940 species in this order. Description Tanaids are small, shrimp-like creatures ranging from in adult size, ...

(superorder

Peracarida The superorder Peracarida is a large group of malacostracan crustaceans, having members in marine, freshwater, and terrestrial habitats. They are chiefly defined by the presence of a brood pouch, or ''marsupium'', formed from thin flattened pla ...

), the last abdominal body segment is fused with the telson, forming a "pleotelson".

Chelicerates

Scorpion_Photograph_By_Shantanu_Kuveskar

The term ''telson'' is widely used for the caudal spine of some

chelicerates The subphylum Chelicerata (from Neo-Latin, , ) constitutes one of the major subdivisions of the phylum Arthropoda. Chelicerates include the sea spiders, horseshoe crabs, and arachnids (including harvestmen, scorpions, spiders, solifuges, tic ...

. The chelicerate telson can be clearly seen in a number of fossil species (like in

eurypterid Eurypterids, often informally called sea scorpions, are a group of extinct marine arthropods that form the Order (biology), order Eurypterida. The earliest known eurypterids date to the Darriwilian stage of the Ordovician period, 467.3 Myr, mil ...

s) and in extant animals (like the

horseshoe crab Horseshoe crabs are arthropods of the family Limulidae and the only surviving xiphosurans. Despite their name, they are not true crabs or even crustaceans; they are chelicerates, more closely related to arachnids like spiders, ticks, and scor ...

"tail" and the

scorpion Scorpions are predatory arachnids of the Order (biology), order Scorpiones. They have eight legs and are easily recognized by a pair of Chela (organ), grasping pincers and a narrow, segmented tail, often carried in a characteristic forward cur ...

sting). Some authorities have urged that the usage of this word in this context be discouraged.

Myriapods

millipedes Millipedes (originating from the Latin , "thousand", and , "foot") are a group of arthropods that are characterised by having two pairs of jointed legs on most body segments; they are known scientifically as the class Diplopoda, the name derive ...

, the telson consists of a legless pre-anal body segment (which may contain a posterior extension known as an ''epiproct''), a pair of anal valves (''paraprocts'') or plates closing off the anus, and a plate below the anus (''hypoproct''), also known as a subanal scale. In

centipedes Centipedes (from Neo-Latin , "hundred", and Latin language, Latin , "foot") are predatory arthropods belonging to the class Chilopoda (Ancient Greek , ''kheilos'', "lip", and Neo-Latin suffix , "foot", describing the forcipules) of the subphyl ...

the telson is the hindmost body segment, posterior to the genital openings, bearing two anal valves.

Hexapods

Protura The Protura, or proturans, and sometimes nicknamed coneheads, are very small (0.6–1.5mm long), soil-dwelling animals, so inconspicuous they were not noticed until the 20th century. The Protura constitute an order of hexapods that were previou ...

ns, an order of minute soil-dwelling animals, are the only hexapods with a telson.The Phylogenetic Positions of Three Basal-Hexapod Groups (Protura, Diplura, and Collembola) Based on Ribosomal RNA Gene Sequences
/ref>

References

{{reflist Crustacean anatomy Arthropod anatomy

Crustaceans

Chelicerates

Myriapods

Hexapods

See also

References