Lancelet

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{{Taxobox | color = pink | name = Lancelets | image = Branchiostoma_lanceolatum.png | image_width = 250px | image_caption = Lancelet (Branchiostoma lanceolatum) | regnum = Animalia | phylum = Chordata | subphylum = Cephalochordata | subphylum_authority = Owen, 1846 | subdivision_ranks = Families | subdivision = 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.

1 Physical features
2 Habitat
3 other facts
4 References
5 Links

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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.

Image:Lancetnikinside.png

brain like blister
notochord
dorsal nerve cord
post-anal tail
anus
food canal
blood system
abdominal porus
overpharynx lacuna
gill's slit
pharynx
mouth lacuna
mimosa
mouth gap
gonads (ovary/testicle)
light sensor
nerves
abdominal ply
liver like sack

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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.

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