telson on:
[Wikipedia]
[Google]
[Amazon]
The telson () is the posterior-most division of the body of an
The term ''telson'' is widely used for the
In
The Phylogenetic Positions of Three Basal-Hexapod Groups (Protura, Diplura, and Collembola) Based on Ribosomal RNA Gene Sequences
/ref>
The telson () is the posterior-most division of the body of an arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...
. 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 A teloblast is a large cell in the embryos of clitellate annelids which asymmetrically divide to form many smaller cells known as blast cells. These blast cells further proliferate and differentiate to form the segmental tissues of the annelid. T ...
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.
In arthropods, an appendage refers to any of the homologous body parts that may extend from a body segment, including ant ...
s, but a forked "tail" called the caudal furca may be present. The shape and composition of the telson differs between arthropod groups.
Crustaceans
Inlobster
Lobsters are a family (Nephropidae, synonym Homaridae) of marine crustaceans. They have long bodies with muscular tails and live in crevices or burrows on the sea floor. Three of their five pairs of legs have claws, including the first pair, ...
s, shrimp
Shrimp are crustaceans (a form of shellfish) with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata of the decapod order, although some crustaceans outside of this order are refer ...
and other decapods
The Decapoda or decapods (literally "ten-footed") are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crabs, lobsters, crayfish, shrimp and prawns. Most decapods are scavengers. The order is es ...
, the telson, along with the uropods, forms the tail fan. This is used as a paddle in the caridoid escape reaction ("lobstering"), whereby an alarmed animal rapidly flexes its tail, causing it to dart backwards. Krill can reach speeds of over 60 cm per second by this means. The trigger 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 (SI) equal to one thousandth (0.001 or 10−3 or 1/1000) of a second and to 1000 microseconds.
A unit of 10 milliseconds may be ca ...
.
In the Isopoda
Isopoda is an order of crustaceans that includes woodlice and their relatives. Isopods live in the sea, in fresh water, or on land. All have rigid, segmented exoskeletons, two pairs of antennae, seven pairs of jointed limbs on the thorax, an ...
and Tanaidacea (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 plat ...
), the last abdominal body segment is fused with the telson, forming a "pleotelson".
Chelicerates
The term ''telson'' is widely used for the caudal spine
Caudal may refer to:
Anatomy
* Caudal (anatomical term) (from Latin ''cauda''; tail), used to describe how close something is to the trailing end of an organism
* Caudal artery, the portion of the dorsal aorta of a vertebrate that passes into the ...
of some chelicerates. The chelicerate telson can be clearly seen in a number of fossil species (like in eurypterids) and in extant animals (like the horseshoe crab "tail" and the scorpion
Scorpions are predatory arachnids of the order Scorpiones. They have eight legs, and are easily recognized by a pair of grasping pincers and a narrow, segmented tail, often carried in a characteristic forward curve over the back and always endi ...
sting). Some authorities have urged that the usage of this word in this context be discouraged.
Myriapods
In millipedes
Millipedes 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 derived from this feature. Each double-legged segment is a resu ...
, 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 the telson is the rear-most body segment, posterior to the genital openings, bearing two anal valves.
Hexapods
Proturans, an order of minute soil-dwelling animals, are the only hexapods with a telson./ref>
See also
*Opisthosoma
The opisthosoma is the posterior part of the body in some arthropods, behind the prosoma ( cephalothorax). It is a distinctive feature of the subphylum Chelicerata (arachnids, horseshoe crabs and others). Although it is similar in most respects ...
* Pygidium
References
{{reflist Crustacean anatomy Arthropod anatomy