Polychelidae

Polychelidae Temporal range: Upper Jurassic–Recent PreꞒ Ꞓ O S D C P T J K Pg N
Stereomastis sculpta
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Malacostraca
Order:	Decapoda
Suborder:	Pleocyemata
Infraorder:	Polychelida
Family:	Polychelidae Wood-Mason, 1874
Genera
Antarcticheles Aguirre-Urreta, Buatois, Chernoglasov & Medina, 1990 † Cardus Galil, 2000 Homeryon Galil, 2000 Pentacheles Bate, 1878 Polycheles Heller, 1862 Willemoesia Grote, 1873

The family Polychelidae contains thirty-eight extant species of blind, benthic lobster-like crustaceans. They are found throughout the world's tropical, sub-tropical and temperate oceans, including the Mediterranean Sea and the Irish Sea.^[1][2]

The family Polychelidae is notable for the number of chelate (clawed) 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 eyestalks 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.^[3]

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). 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 (330 ft) to over 5,000 metres (16,000 ft). This also accounts for the lack of eyesight, since almost none of the sun's light penetrates to such abyssal depths.

A single fossil species is known, Antarcticheles antarcticus, which was found in Jurassic sediments on James Ross Island, close to the Prince Gustav Channel.^[4]

The larvae 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.