Denominadas pelagosferas, as larvas de muitas espécies de sipuncúlidos são transparentes e nadam livres na água por meses antes de se transformarem no adulto, que tem aspecto vermiforme e vive enterrado na areia ou lodo.
The subphylum Cephalochordata (called vernacularly as lancelets) is represented by a small (up to 6 cm long) animals characterized to have the notochord as an axial organ throughout the whole body length. The lancelet body plan is similar to that of fishes and other vertebrates: dorsally-situated neural tube, and ventrally-situated alimentary system sandwiched laterally with myotomes (or myomeres), arranged as a series of segmented muscle blocks on each side. They are exclusively marine, inhabiting intertidal to subtidal sandy bottoms in boreal to tropical waters around the world. Recently, however, the true deep-sea species was firstly described. The adults have at benthic life within the superficial layer of bottom sediment, and are filter-feeders. Adults can also swim, but only rarely and sporadically.
