? Lancelets
Lancelet (Branchiostoma lanceolatum)
Scientific classification
Kingdom: Animalia Phylum: Chordata Subphylum: Cephalochordata Owen, 1846
Families
Asymmetronidae Branchiostomidae

The lancelets (subphylum Cephalochordata, and traditionally known as the amphioxus) are a group of primitive chordates. They are an important object of study in zoology as they provide indications about the origins of the vertebrates. Image File history File links Branchiostoma_lanceolatum. ... Scientific classification or biological classification is how biologists group and categorize extinct and living species of organisms (as opposed to folk taxonomy). ... Binomial name Aptenodytes forsteri Gray, 1844 For other uses, see Animal (disambiguation). ... Typical Classes Subphylum Urochordata - Tunicates Ascidiacea Thaliacea Larvacea Subphylum Cephalochordata - Lancelets Subphylum Myxini - Hagfishes Subphylum Vertebrata - Vertebrates Petromyzontida - Lampreys Placodermi (extinct) Chondrichthyes - Cartilaginous fishes Acanthodii (extinct) Actinopterygii - Ray-finned fishes Actinistia - Coelacanths Dipnoi - Lungfishes Amphibia - Amphibians Reptilia - Reptiles Aves - Birds Mammalia - Mammals Chordates (phylum Chordata) include the vertebrates, together with... Sir Richard Owen and Dinornis bird skeleton Sir Richard Owen (July 20, 1804 - December 18, 1892) was an English biologist, comparative anatomist and palaeontologist. ... Typical Classes Subphylum Urochordata - Tunicates Ascidiacea Thaliacea Larvacea Subphylum Cephalochordata - Lancelets Subphylum Myxini - Hagfishes Subphylum Vertebrata - Vertebrates Petromyzontida - Lampreys Placodermi (extinct) Chondrichthyes - Cartilaginous fishes Acanthodii (extinct) Actinopterygii - Ray-finned fishes Actinistia - Coelacanths Dipnoi - Lungfishes Amphibia - Amphibians Reptilia - Reptiles Aves - Birds Mammalia - Mammals Chordates (phylum Chordata) include the vertebrates, together with... Typical classes Petromyzontidae (lampreys) Placodermi - extinct Chondrichthyes (cartilaginous fish) Acanthodii - extinct Actinopterygii (ray-finned fish) Actinistia (coelacanths) Dipnoi (lungfish) Amphibia (amphibians) Reptilia (reptiles) Aves (birds) Mammalia (mammals) Vertebrata is a subphylum of chordates, specifically, those with backbones or spinal columns. ...

Physical features

In common with the vertebrates, lancelets have a nerve cord running along their back, pharyngeal gill slits and a tail that runs past the anus. Also like humans, muscles are banded. Unlike the vertebrates however the dorsal nerve chord is not protected by bone, but a rather simpler notochord made up of a cylinder of cells that are closely-packed to form a toughened membrane. The lancelet notochord, unlike the vertebrate spine, extends into the head. This gives the subphylum its name ("cephalo-" meaning "relating to the head"). The lancelets also have oral cirri, thin tentacle-like strands that fall in front of the mouth that act as sensory devices and as a filter for the water passing into the body. The water exits the body via the atriopore. A characteristic of Chordates. ... The notochord is a flexible rod-shaped body found in embryos of all chordates. ...

Download high resolution version (1600x529, 242 KB) Wikipedia does not have an article with this exact name. ...

1. brain like blister
2. notochord
3. dorsal nerve cord
4. post-anal tail
5. anus
6. food canal
7. blood system
8. abdominal porus
9. overpharynx lacuna
10. gill's slit
11. pharynx
12. mouth lacuna
13. mimosa
14. mouth gap
15. gonads (ovary/testicle)
16. light sensor
17. nerves
18. abdominal ply
19. liver like sack

Habitat

Lancelets grow up to about five centimetres long, being eight centimeters at the longest. They are usually found buried in sand in shallow parts of temperate or tropical seas. In Asia, they are harvested commercially.

Taxonomy

Cephalochordata is traditionally seen as a sister subphylum to the vertebrates, and are grouped together as a sister group (sometimes called notochordata) to the simpler still urochordates. But newer research shows this is not the case. It is the urochordates who are the sister group of the vertebrates, while cephalochordata is the most original and primitive subhylum of the chordates. The asymmetric nature of juveniles is unique to the cephlochordates, and proves that lancelets do not contain an ancestor of the vertebrates. Vertebrata is a subphylum of chordates, specifically, those with backbones or spinal columns. ... Classes Ascidiacea Thaliacea Appendicularia Urochordata (sometimes known as tunicata and commonly called urochordates, tunicates or sea squirts) is the subphylum of saclike filter feeders with input and output siphons. ...

The following are the species recognised by ITIS. Other sources (see for instance Tudge) show that there are 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

References

• Colin Tudge (2000). The Variety of Life, Oxford University Press. ISBN 0198604262.
• Cephalochordata from Berkeley

Colin Tudge (born 22 April 1943) is a biologist by training and a British science writer who is the author of numerous works on food, agriculture, genetics, and species diversity. ... This article is about the year 2000. ...

Links

• Error in the Genealogy of Human
• The Amphioxus Song