Polychelidae
Encyclopedia
The family Polychelidae contains thirty-eight extant species
of blind
, benthic lobster
-like crustacean
s. They are found throughout the world's tropical, sub-tropical and temperate
ocean
s, including the Mediterranean Sea
and the Irish Sea
.
ed) limbs, with either four or all five pairs of pereiopods bearing claws. This gives rise to the scientific names 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
is very short or absent, and, although eyestalk
s are present, the eyes are absent. This family can be seen as evidence of the transition from shrimp
-like animals to lobster
-like animals, since they possess a number of primitive characters (plesiomorphies), such as the pointed telson
, in contrast to the rounded telson in lobsters.
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
). 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
, this made the Polychelidae something of a living fossil
.
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 100 metres (328.1 ft) to over 5000 metres (16,404.2 ft). This also accounts for the lack of eyesight, since almost none of the sun's light penetrates to such abyssal
depths.
sediments on James Ross Island
, close to the Prince Gustav Channel
.
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.
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...
of blind
Blindness
Blindness is the condition of lacking visual perception due to physiological or neurological factors.Various scales have been developed to describe the extent of vision loss and define blindness...
, benthic lobster
Lobster
Clawed lobsters comprise a family of large marine crustaceans. Highly prized as seafood, lobsters are economically important, and are often one of the most profitable commodities in coastal areas they populate.Though several groups of crustaceans are known as lobsters, the clawed lobsters are most...
-like crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s. They are found throughout the world's tropical, sub-tropical and temperate
Temperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
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, including the Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
and the Irish Sea
Irish Sea
The Irish Sea separates the islands of Ireland and Great Britain. It is connected to the Celtic Sea in the south by St George's Channel, and to the Atlantic Ocean in the north by the North Channel. Anglesey is the largest island within the Irish Sea, followed by the Isle of Man...
.
Anatomy
The family Polychelidae is notable for the number of chelate (clawClaw
A claw is a curved, pointed appendage, found at the end of a toe or finger in most mammals, birds, and some reptiles. However, the word "claw" is also often used in reference to an invertebrate. Somewhat similar fine hooked structures are found in arthropods such as beetles and spiders, at the end...
ed) limbs, with either four or all five pairs of pereiopods bearing claws. This gives rise to the scientific names 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 (anatomy)
The term rostrum is used for a number of unrelated structures in different groups of animals:*In crustaceans, the rostrum is the forward extension of the carapace in front of the eyes....
is very short or absent, and, although eyestalk
Eyestalk
In anatomy, an eyestalk is a protrusion that extends the eye away from the body, giving the eye a better field of view than if it were unextended. It is common in nature and in fiction....
s are present, the eyes are absent. This family can be seen as evidence of the transition from shrimp
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
-like animals to lobster
Lobster
Clawed lobsters comprise a family of large marine crustaceans. Highly prized as seafood, lobsters are economically important, and are often one of the most profitable commodities in coastal areas they populate.Though several groups of crustaceans are known as lobsters, the clawed lobsters are most...
-like animals, since they possess a number of primitive characters (plesiomorphies), such as the pointed telson
Telson
The telson is the last division of the body of a crustacean. It is not considered a true segment because it does not arise in the embryo from teloblast areas as do real segments. It never carries any appendages, but a forked "tail" called the caudal furca is often present. Together with the...
, 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 expeditionChallenger expedition
The Challenger expedition of 1872–76 was a scientific exercise that made many discoveries to lay the foundation of oceanography. The expedition was named after the mother vessel, HMS Challenger....
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
Charles Spence Bate, or Spence Bate, FRS was a British zoologist and dentist, who who practiced first at Swansea, and then Plymouth, taking over his father's practice. He was an authority on the Crustacea, and a frequent correspondent of Charles Darwin, mostly concerning their shared interest in...
). Their kinship with the fossil group Eryonoidea, including well-known genera such as Eryon
Eryon
Eryon, meaning red , is an extinct genus of decapod crustaceans from the Late Jurassic of Germany. Its remains are known from the Solnhofen limestone. It reached a length of around , and may have fed on particulate matter on the sea bed....
, was immediately recognised. Since Eryon and its relatives were only known from fossils, lastly in the Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
, this made the Polychelidae something of a living fossil
Living fossil
Living fossil is an informal term for any living species which appears similar to a species otherwise only known from fossils and which has no close living relatives, or a group of organisms which have long fossil records...
.
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 100 metres (328.1 ft) to over 5000 metres (16,404.2 ft). This also accounts for the lack of eyesight, since almost none of the sun's light penetrates to such abyssal
Abyssal zone
The abyssal zone is the abyssopelagic layer or pelagic zone that contains the very deep benthic communities near the bottom of oceans. "Abyss" derives from the Greek word ἄβυσσος, meaning bottomless. At depths of 4,000 to 6,000 metres , this zone remains in perpetual darkness and never receives...
depths.
Fossil record
A single fossil species is known, Antarcticheles antarcticus, which was found in JurassicJurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
sediments on James Ross Island
James Ross Island
James Ross Island is a large island off the southeast side and near the northeastern extremity of Antarctic Peninsula, from which it is separated by Prince Gustav Channel. Rising to , it is irregularly shaped and extends in a north-south direction. It was charted in October 1903 by the Swedish...
, close to the Prince Gustav Channel
Prince Gustav Channel
The Prince Gustav Channel was named in 1903 after Crown Prince Gustav of Sweden by Otto Nordenskiöld of the Swedish Antarctic Expedition.The channel is bounded on the west by the Antarctic Peninsula and on the east by James Ross Island...
.
Larvae
The larvaLarva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
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 Heller, 1862
- Polycheles aculeatus Galil, 2000
- Polycheles auriculatus (Bate, 1878)
- Polycheles baccatus Bate, 1878
- Polycheles ceratus Alcock, 1878
- Polycheles coccifer Galil, 2000
- Polycheles enthrix (Bate, 1878)
- Polycheles evexus Galil, 2000
- Polycheles galil Ahyong & Brown, 2002
- Polycheles helleri Bate, 1878
- Polycheles kermadecensis Ahyong and Brown, 2002
- Polycheles nanus (S. I. Smith, 1884)
- Polycheles pacificus (Faxon, 1893)
- Polycheles perarmatus Holthuis, 1952
- Polycheles phosphorus (Alcock, 1894)
- Polycheles politus Galil, 2000
- Polycheles sculptusPolycheles sculptusPolycheles sculptus is a species of "strange, blind crustacean". It has a cosmopolitan distribution in deep water, being found on both sides of the Atlantic Ocean, in the Mediterranean Sea, and across much of the Indo-West Pacific, at depths of ....
S. I. Smith, 1880 - Polycheles suhmi (Bate, 1878)
- Polycheles surdus Galil, 2000
- Polycheles talismani (Bouvier, 1917)
- Polycheles tanneri Faxon, 1893
- Polycheles trispinosus (De Man, 1905)
- Polycheles typhlopsPolycheles typhlopsPolycheles typhlops is a species of blind, deep water decapod crustacean with a cosmopolitan distribution. It is "one of the dominant and most characteristic crustaceans in deep-sea communities of the Mediterranean Sea".-Description:...
Heller, 1862
- Antarcticheles Aguirre-Urreta, Buatois, Chernoglasov & Medina, 1990
- Antarcticheles antarcticus Aguirre-Urreta, Buatois, Chernoglasov & Medina, 1990
- CardusCardus cruciferCardus crucifer is a species of blind deep-water decapod crustacean from the Atlantic Ocean, the only species in the genus Cardus. It differs from other members of the family Polychelidae in having only four pairs of claws, instead of five, in both sexes. The name Cardus refers to the thistle...
Galil, 2000- Cardus cruciferCardus cruciferCardus crucifer is a species of blind deep-water decapod crustacean from the Atlantic Ocean, the only species in the genus Cardus. It differs from other members of the family Polychelidae in having only four pairs of claws, instead of five, in both sexes. The name Cardus refers to the thistle...
(Thomson, 1873)
- Cardus crucifer
- HomeryonHomeryonHomeryon is a genus of blind, deep-sea crustaceans. It is named after the blind Greek poet Homer and the genus Eryon, which contains fossil relatives of the modern Polychelidae...
Galil, 2000- Homeryon armarium Galil, 2000
- Homeryon asper (Rathbun, 1906)
- Pentacheles Bate, 1878
- Pentacheles gibbus Alcock, 1894
- Pentacheles laevis Bate, 1878
- Pentacheles obscurus Bate, 1878
- Pentacheles snyderii (Rathbun, 1906)
- Pentacheles validus A. Milne-Edwards, 1880
- Willemoesia Grote, 1873
- Willemoesia forceps A. Milne Edwards, 1880
- Willemoesia inornata Faxon, 1893
- Willemoesia leptodactyla (Willemoes-Suhm, 1875)
- Willemoesia pacifica Sund, 1920