Question

Describe the development of amphioxus up to the formation of coelom

Answer 1

The three‐dimensional structure of organisms is characterized by the three perpendicular body axis, namely, the anterior–posterior, dorsal–ventral, and left–right axes. These axes generally emerge in the early embryonic stage, and are sometimes already apparent in eggs before fertilization.

Answer 2

Answer:

• Branchiostoma (Amphioxus) develops indirectly through a larval stage. Branchiostoma's early embryology is straightforward.
• As a result, unlike in any other vertebrate, the development of an egg, which has less yolk, into a complex and distinct animal is much simpler to observe.
• External fertilization occurs in the seawater surrounding the area where eggs and spermatozoa are discharged.
• The ovum has an exterior thin vitelline membrane that surrounds a peripheral cytoplasmic layer, a core yolky cytoplasm that is mostly directed toward the vegetal pole, and a fluid-filled germinal sac or nucleus that is directed toward the animal pole before fertilization.
• Complete or holoblastic cleavage with about equal type is present.
• The egg undergoes its first cleavage along its median axis, resulting in two blastomeres of equal size, the right and left, which together produce the right side and left side of the adult animal.
• The first two blastomeres are split into four equal-sized blastomeres by the second cleavage, which is also meridional but occurs at a right angle to the first.
• The fifth cleavage, which results in thirty-two cells grouped in four layers, is latitudinal or horizontal and synchronous.
• Sixth cleavage produces 64 blastomeres and is meridional and synchronous.
• Up to this point, subsequent cleavages won't be synchronous; the blastomeres will still be loosely packed together to create the morula. In the interim, a semifluid substance gathers in the morula's center.
• During additional splitting of the morula, it forces all of the blastomeres outward so that they are arranged in a single layer called blastoderm that encloses a central cavity filled with fluid, or blastocoel.
• The blastula refers to this stage of development, while the coeloblastula of Amphioxus is a blastula that has fully matured.

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