Polychelidae
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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.
Anatomy
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.
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). 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.
Fossil record
A single fossil species is known, Antarcticheles antarcticus, which was found in Jurassic sediments on James Ross Island, close to the Prince Gustav Channel.
Larvae
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.
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 suhmi (Bate, 1878) Polycheles surdus Galil, 2000 Polycheles talismani (Bouvier, 1917) Polycheles tanneri Faxon, 1893 Polycheles trispinosus (De Man, 1905) Polycheles typhlops Heller, 1862
- †Antarcticheles Aguirre-Urreta, Buatois, Chernoglasov & Medina, 1990 †Antarcticheles antarcticus Aguirre-Urreta, Buatois, Chernoglasov & Medina, 1990
- Cardus Galil, 2000 Cardus crucifer (Thomson, 1873)
- Homeryon 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
- †Angusteryon Audo & Furrer, 2020 Augusteryon oberlii