AskDefine | Define lancelet

Dictionary Definition

lancelet n : small translucent lancet-shaped burrowing marine animal; primitive forerunner of the vertebrates [syn: amphioxus]

User Contributed Dictionary

English

Noun

  1. any of a group of primitive marine animals, of subphylum Cephalochordata, having a notochord instead of a backbone

Extensive Definition

The lancelets (subphylum Cephalochordata, traditionally known as amphioxus) are a group of primitive chordates. They are usually found buried in sand in shallow parts of temperate or tropical seas. In Asia, they are harvested commercially for food for humans and domesticated animals. They are an important object of study in zoology as they provide indications about the origins of the vertebrates.

Physical features

Lancelets grow up to about five centimetres long, reaching eight centimetres at the longest. In common with vertebrates, lancelets have a nerve cord running along the back, pharyngeal slits and a tail that runs past the anus. Also like vertebrates, the muscles are arranged in blocks called myomeres. Unlike vertebrates, the dorsal nerve cord is not protected by bone but by a simpler notochord made up of a cylinder of cells that are closely-packed to form a toughened rod. The lancelet notochord, unlike the vertebrate spine, extends into the head. This gives the subphylum its name (cephalo- meaning 'relating to the head'). Lancelets also have oral cirri, thin tentacle-like strands that hang in front of the mouth and act as sensory devices and as a filter for the water passing into the body. The water exits the body via the atriopore.
  1. brain-like blister
  2. notochord
  3. dorsal nerve cord
  4. post-anal tail
  5. anus
  6. food canal
  7. circulatory system
  8. atriopore
  9. overpharynx lacuna
  10. gill slit
  11. pharynx
  12. vestibule
  13. oral cirri
  14. mouth opening
  15. gonads (ovary/testicle)
  16. light sensor
  17. nerves
  18. metapleural fold
  19. hepatic caecum (liver-like sack)

Taxonomy

Cephalochordata is traditionally seen as a sister subphylum to the vertebrates, with whom they are grouped together as a sister group (sometimes called Notochordata) to the simpler still Urochordata. But newer research suggests this may not be the case. Urochordates may be the sister group of the vertebrates, while Cephalochordata may be the most basal subphylum of the chordates. The asymmetric nature of juveniles is unique to the cephalochordates and indicates (as do certain other features, including the seriated gonads) that lancelets are, at least, more derived than would be expected of a "living fossil" representative of basal chordates.
The following are the species recognised by ITIS. Other sources (see for instance Tudge) show that there might be up to thirty species.
  • Family Asymmetronidae
    • Genus Asymmetron
      • Asymmetron lucayanum
      • Asymmetron maldivense
    • Genus Epigonichthys
  • Family Branchiostomidae
    • Genus Branchiostoma
      • Branchiostoma belcheri
      • Branchiostoma californiense
      • Branchiostoma capense
      • Branchiostoma caribaeum
      • Branchiostoma floridae
      • Branchiostoma lanceolatum
      • Branchiostoma valdiviae
      • Branchiostoma virginiae

In music

Folk musician and marine biologist Sam Hinton performed a song attributed to Dr. Sewell H. Hopkins about Amphioxus entitled It's a Long Way from Amphioxus. Sung to the tune of "It's a Long Way to Tipperary," the ditty references now-disputed notions about the place of cephalochordates in the chordate evolutionary timeline:
It's a long way from Amphioxus, It's a long way to us, It's a long way from Amphioxus To the meanest human cuss. It's good-bye, fins and gill-slits, Welcome, lungs and hair! It's a long, long way from Amphioxus, But we all came from there.
lancelet in Catalan: Cefalocordat
lancelet in Czech: Bezlebeční
lancelet in German: Lanzettfischchen
lancelet in Estonian: Süstikkalad
lancelet in Spanish: Cephalochordata
lancelet in Esperanto: Brankiostomulo
lancelet in French: Cephalochordata
lancelet in Korean: 두색동물
lancelet in Croatian: Kopljače
lancelet in Italian: Branchiostoma
lancelet in Hebrew: מיתרני ראש
lancelet in Lithuanian: Iešmutis
lancelet in Hungarian: Fejgerinchúrosok
lancelet in Macedonian: Амфиоксус
lancelet in Dutch: Schedellozen
lancelet in Japanese: ナメクジウオ
lancelet in Norwegian: Lansettfisker
lancelet in Occitan (post 1500): Cephalochordata
lancelet in Polish: Bezczaszkowce
lancelet in Portuguese: Cephalochordata
lancelet in Russian: Головохордовые
lancelet in Simple English: Lancelet
lancelet in Slovak: Kopijovce
lancelet in Serbian: Копљаши
lancelet in Finnish: Suikulaiset
lancelet in Swedish: Lansettfiskar
lancelet in Ukrainian: Головохордові
lancelet in Chinese: 文昌鱼
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