Lancelet - Taxonomy

Taxonomy

The Cephalochordata is traditionally seen as a sister subphylum to the vertebrates, with which it is grouped together into a clade (sometimes called Notochordata) which in turn is the sister group to the simpler still Urochordata. Newer research suggests this may not be the case. The Cephalochordata may be the most basal subphylum of the chordates, while the sister group of the vertebrates may be the tunicates, previously known as the urochordates. However, other recent molecular studies (cit. in Benton 2005: 8) place cephalochordates nearer to vertebrates, and "ost authors regard amphioxus as the closest relative of the Vertebrata on the basis of 10–15 features that are not seen in tunicates".

The asymmetric nature of juveniles is unique to the cephalochordates and demonstrates (as do certain other features, including the seriated gonads) that lancelets are more derived than would be expected. This is a reminder that the "living fossil" representative of a basal clade has as long an evolutionary history as any other living thing, and thus is more derived than the actual primitive ancestor it otherwise so closely resembles.

The following are the species recognised by ITIS. Other sources, for instance Tudge, show that there might be up to thirty species.

• Family Asymmetronidae
  • Genus Asymmetron
    • Asymmetron lucayanum
    • Asymmetron maldivense
  • Genus Epigonichthys
    • Epigonichthys australis
    • Epigonichthys bassanus
    • Epigonichthys cingalense
    • Epigonichthys cultellus
    • Epigonichthys hectori
    • Epigonichthys lucayanum
    • Epigonichthys maldivensis
• Family Branchiostomidae
  • Genus Branchiostoma
    • Branchiostoma belcheri
    • Branchiostoma californiense
    • Branchiostoma capense
    • Branchiostoma caribaeum
    • Branchiostoma clonaseum
    • Branchiostoma floridae
    • Branchiostoma lanceolatum
    • Branchiostoma minucauda
    • Branchiostoma moretonensis
    • Branchiostoma valdiviae
    • Branchiostoma virginiae