Phylum Chordata Class Cephalochordata Number of families 1
Exclusively marine species with slender, fish-like shape, tapered at both ends; easily recognized by the externally visible v-shaped lines that separate the iterated muscle blocks and by the oral cirri that guard the mouth opening against unwarranted particles
Photo: Lancelet (Amphioxus lanceolatus) larva head. Lancelets have no heart but do have gills. (Photo by Animals Animals ©P. Parks, OSF. Reproduced by permission.)
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