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. Lancelets serve as an intriguing comparison point for tracing how vertebrates have evolved and adapted. Although lancelets split from vertebrates more than 520 million years ago, its genome holds clues about evolution, particularly how vertebrates have employed old genes for new functions.
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.
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.
Laboratory spawning and development of the Bahama lancelet, Asymmetron lucayanum (Cephalochordata): fertilization through feeding larvae.(Report)
Oct 01, 2010; Introduction The phylum Chordata comprises three extant clades--Cephalochordata, Tunicata, and Vertebrata--with the first,...
Phylogenetic position of a whale-fall lancelet (Cephalochordata) inferred from whole mitochondrial genome sequences.(Research article)(Report)
Jul 31, 2007; Authors: Takeshi Kon (corresponding author) ; Masahiro Nohara ; Yusuke Yamanoue ; Yoshihiro Fujiwara ; Mutsumi...