[7][8][9] Branchiostoma belcheri exhibit all basic characteristics of the Chordata phylum including the notochord, dorsal nerve cord, pharynx, buccal cavity, cirri, tail, dorsal fin, nerve cord, segmented muscle, and ocelli.
[1][3] The notochord runs down the animal's back with a smooth layer of connective tissue on the exterior, lining an interior core of cells that are loosely packed and contain fluid-filled spaces.
[1] The outer sheath resists changes in fluid pressure in the notochord, allowing for flexibility while simultaneously withstanding contraction.
This is a distinguishing characteristic from other worm types as the anus is located all the way at the bottom, on the back side of animal.
Finally, muscle allows for movement and maintenance of bodily position, which can be found in discrete segments along the sides of the body.
[14] They reproduce during the spawning season, which takes place every year for approximately three to six month, and occurs during the spring and summer.
[6] The gametes undergo development such that they exhibit ten distinct periods: zygote, cleavage, blastula, gastrula, neurula, talibud, larva, metamorphosis, juvenile, and adult.
This growth period varies in duration depending on the species, ranging from a few weeks in those characterized as "tropical" to several years for those identified as "temperate".
They use their mouths to suck in large amounts of water, forcing it out via the slits and holding onto small food particles in the process.
Thus, they feed on microorganisms existing in the water taken up by ciliary action during respiration and brought into the pharyngeal cavity.
[17] Later observations concluded that amphioxus in waters other than the Ariake Sea and the Amakusa belonged to B. belcheri var.
[18] Amphioxus distribution shows large population numbers in the central portion of Ariake sea, as well as four locations surrounding the Amakusa Islands.
[8][9] Additionally, aquacultural expansion, illegal fishing, sand mining and sediment transportation, and increasing maritime traffic all contribute to the elimination of amphioxus, as well as destruction of their habitat.
[8] The occurrence of the amphioxus in the Ariake Sea was reported upon discovery of a small animal, similar to that of a fish, that was referred to as "itachi-uo" by the locals.
[17] Branchiostoma belcheri is related to other species of Branchiostoma as it is marine, distributed in shallow waters, positioned with its anterior end in the sand, mostly sedentary, has a small, slender body, is segmented and transparent, has a trunk, tail, median fins, myotomes, notochord, complete digestive tract, and dorsal nerve cord, is enterocoelous, respirates across body surface, uses protonephridia with solenocytes for excretion, performs external fertilization, has separate sexes and exhibits indirect development.