Pikaia gracilens is an extinct invertebrate animal described from the wonderful pre-cambrian soft-bodied fossils of the burgess shale in british columbia. examinations by paleontologists have revealed that organisms belonging to this species had a prominent notochord and segmental muscles. from this information, you could conclude that it is closely related to

Lancelets

Explanation:

ancelet, name for little, fishlike lower chordate (see Chordata), likewise called amphioxus; it demonstrates numerous affinities with the vertebrates. There are around 30 lancelet species, most having a place with the class Brachiostoma (once in the past Amphioxus). Lancelets are more often than not around 1 inch long, with straightforward bodies decreased at the two finishes. There is no unmistakable head and no combined blades. Lancelets are channel feeders and live in shallow marine waters; they can swim through water or wet sand, yet are typically discovered covered in the sand with just the mouth end anticipating. Little nourishment particles enter the pharynx through the mouth and are sifted through as the water exits through the gill cuts. Breath presumably happens for the most part through the skin. The utilization of the gill cuts for sustaining instead of breath is normal for the lower chordates

The lancelet has a dorsal notochord, or solidifying bar, stretching out from tip to tail, that gives it its trademark pointed shape. It holds the notochord as the major skeletal help all through life; in vertebrates the notochord is encompassed and for the most part supplanted by a vertebral section during embryonic advancement. In the lancelet there is a nerve string over the notochord, yet no mind and no eyes. A ventral vein conveys the boring blood; there is no heart. It is imagined that vertebrates developed from precursors like lancelets. The hatchling of the lamprey, the most crude living vertebrate, looks like a lancelet in numerous regards. Lancelets are grouped in the phylum Chordata, subphylum Cephalochordata.

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the relative atomic mass of an element is the mass of one atom of that element, relative to 1/12th of the mass of a  1212c atom. to convert to an absolute mass in kg, it is necessary to multiply by  1.661×10−271.661×10−27.

the relative atomic mass is roughly equal to the number of neutrons, plus the number of protons, in the nucleus of the atom.

for elements with more than one stable isotope (different types of nucleus with different numbers of neutrons but the same number of protons), the quoted mass is usually the average mass, weighted by the relative abundance of the different isotopes.