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The family Polychelidae contains thirty-eight extant
species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
of blind,
benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word (), meaning "the depths". ...
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 ...
-like
crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...
s. They are found throughout the world's
tropical The tropics are the regions of Earth surrounding the equator, where the sun may shine directly overhead. This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's ax ...
,
sub-tropical The subtropical zones or subtropics are geographical and climate zones immediately to the north and south of the tropics. Geographically part of the temperate zones of both hemispheres, they cover the middle latitudes from to approximately 3 ...
and
temperate In geography, the temperate climates of Earth occur in the middle latitudes (approximately 23.5° to 66.5° N/S of the Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ran ...
ocean The ocean is the body of salt water that covers approximately 70.8% of Earth. The ocean is conventionally divided into large bodies of water, which are also referred to as ''oceans'' (the Pacific, Atlantic, Indian Ocean, Indian, Southern Ocean ...
s, including the
Mediterranean Sea The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern Eur ...
and the
Irish Sea The Irish Sea is a body of water that separates the islands of Ireland and Great Britain. It is linked to the Celtic Sea in the south by St George's Channel and to the Inner Seas off the West Coast of Scotland in the north by the North Ch ...
.


Anatomy

The family Polychelidae is notable for the number of chelate (
claw A claw is a curved, pointed appendage found at the end of a toe or finger in most amniotes (mammals, reptiles, birds). Some invertebrates such as beetles and spiders have somewhat similar fine, hooked structures at the end of the leg or Arthro ...
ed) limbs, with either four or all five pairs of
pereiopod The anatomy of a decapod consists of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment – often called a somite – may possess one pair of appendages, although in various groups these m ...
s bearing claws. This gives rise to the
scientific name In Taxonomy (biology), taxonomy, binomial nomenclature ("two-term naming system"), also called binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin gramm ...
s ''Polycheles'' (many-clawed) and ''Pentacheles'' (five claws). The first pair of periopods are greatly elongated, but often become broken off while specimens are being brought to the surface. The
rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit ** podium * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ...
is very short or absent, and, although
eyestalk In anatomy, an eyestalk (sometimes spelled eye stalk and also known as an ommatophore) is a protrusion that extends an eye away from the body, giving the eye a better field of view. It is a common feature in nature and frequently appears in fict ...
s are present, the
eye An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system. In higher organisms, the ey ...
s are absent. This family can be seen as evidence of the transition from
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 ...
-like animals to
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 ...
-like animals, since they possess a number of primitive characters (plesiomorphies), such as the pointed
telson The telson () is the hindmost division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment (biology), segment of the arthropod body, or an additional division that is not a true segm ...
, in contrast to the rounded telson in lobsters.


Discovery

Although apparently widespread, and at least locally common, they were first discovered only in the late nineteenth century when they were dredged up by the ''Challenger'' expedition from a depth supposed to be "barren, if not of all life, certainly of animals so high in the scale of existence" (
Charles Spence Bate Charles Spence Bate, (16 March 1819 – 29 July 1889) was a British zoologist and dentist. Life Charles Spence Bate was born at Trenick House near Truro, the son of Charles Bate (1789–1872) and Harriet Spence (1788–1879). Charles adopte ...
). Their kinship with the fossil group Eryonoidea, including well-known genera such as '' Eryon'', was immediately recognised. Since ''Eryon'' and its relatives were only known from fossils, lastly in the
Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...
, this made the Polychelidae something of a
living fossil A living fossil is a Deprecation, deprecated term for an extant taxon that phenotypically resembles related species known only from the fossil record. To be considered a living fossil, the fossil species must be old relative to the time of or ...
. The reason that polychelids remained unknown for so long is that they live on the sea-floor, often at great depths; the family as a whole has a depth range from less than to over . This also accounts for the lack of eyesight, since almost none of the sun's light penetrates to such
abyssal The abyssal zone or abyssopelagic zone is a layer of the pelagic zone of the ocean. The word ''abyss'' comes from the Greek word (), meaning "bottomless". At depths of , this zone remains in perpetual darkness. It covers 83% of the total area o ...
depths.


Fossil record

A single fossil species is known, '' Antarcticheles antarcticus'', which was found in
Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...
sediments on
James Ross Island James Ross Island () is a large island off the southeast side and near the northeastern extremity of the Antarctic Peninsula, from which it is separated by Prince Gustav Channel. Rising to , it is irregularly shaped and extends in a north–so ...
, close to the
Prince Gustav Channel The Prince Gustav Channel () is a strait about long and from wide, separating James Ross Island and Vega Island from the Trinity Peninsula, Antarctica. Location Prince Gustav Channel is in Graham Land on the southeast coast of the Trinity Pen ...
.


Larvae

The
larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...
e of polychelids are very distinctive, and were first described under the name ''Eryoneicus''. Over forty different larval forms are known, although few can be ascribed to known adult species.


Classification

*'' Polycheles'' **'' Polycheles aculeatus'' **'' Polycheles auriculatus'' **''
Polycheles baccatus ''Polycheles'' is a genus of decapods within the family Polychelidae, with 9 current species assigned to it. Members of this genus are found in oceans worldwide at depths of 665 to 938 meters. Species * ''Polycheles amemiyai'' * '' Polycheles b ...
'' **'' Polycheles ceratus'' **''
Polycheles coccifer ''Polycheles'' is a genus of decapods within the family Polychelidae, with 9 current species assigned to it. Members of this genus are found in oceans worldwide at depths of 665 to 938 meters. Species * ''Polycheles amemiyai'' * ''Polycheles ba ...
'' **''
Polycheles enthrix ''Polycheles'' is a genus of decapods within the family Polychelidae, with 9 current species assigned to it. Members of this genus are found in oceans worldwide at depths of 665 to 938 meters. Species * ''Polycheles amemiyai'' * ''Polycheles ba ...
'' **'' Polycheles evexus'' **''
Polycheles galil ''Polycheles'' is a genus of Decapoda, decapods within the family Polychelidae, with 9 current species assigned to it. Members of this genus are found in oceans worldwide at depths of 665 to 938 meters. Species * ''Polycheles amemiyai'' * ''Pol ...
'' **'' Polycheles helleri'' **''
Polycheles kermadecensis ''Polycheles'' is a genus of decapods within the family Polychelidae, with 9 current species assigned to it. Members of this genus are found in oceans worldwide at depths of 665 to 938 meters. Species * ''Polycheles amemiyai'' * ''Polycheles ba ...
'' **'' Polycheles nanus'' **'' Polycheles pacificus'' **''
Polycheles perarmatus ''Polycheles'' is a genus of decapods within the family Polychelidae, with 9 current species assigned to it. Members of this genus are found in oceans worldwide at depths of 665 to 938 meters. Species * ''Polycheles amemiyai'' * ''Polycheles ba ...
'' **'' Polycheles phosphorus'' **'' Polycheles politus'' **'' Polycheles suhmi'' **'' Polycheles surdus'' **'' Polycheles talismani'' **''
Polycheles tanneri ''Polycheles'' is a genus of decapods within the family Polychelidae, with 9 current species assigned to it. Members of this genus are found in oceans worldwide at depths of 665 to 938 meters. Species * ''Polycheles amemiyai'' * ''Polycheles ba ...
'' **'' Polycheles trispinosus'' **''
Polycheles typhlops ''Polycheles typhlops'' is a species of blindness, blind, deep water Decapoda, decapod crustacean with a cosmopolitan distribution. It is "one of the dominant and most characteristic crustaceans in deep-sea communities of the Mediterranean Sea". ...
'' *''† Antarcticheles'' **''† Antarcticheles antarcticus'' *''
Cardus The Cardus Institute is a Christian think tank based in Hamilton, Ontario. It was founded in 1974 as the Work Research Foundation. Through a variety of research, publishing, and programmatic activities, the organization advocates for religion an ...
'' **'' Cardus crucifer'' *'' Homeryon'' **'' Homeryon armarium'' **'' Homeryon asper'' *'' Pentacheles'' **'' Pentacheles gibbus'' **'' Pentacheles laevis'' **'' Pentacheles obscurus'' **'' Pentacheles snyderii'' **'' Pentacheles validus'' *'' Willemoesia'' **'' Willemoesia forceps'' **'' Willemoesia inornata'' **'' Willemoesia leptodactyla'' **'' Willemoesia pacifica'' *'' Angusteryon'' **'' Augusteryon oberlii''


References

{{Taxonbar, from=Q1674573 Polychelida Taxa named by James Wood-Mason Decapod families