Spiral cleavage - metazoa, Biology

Spiral Cleavage - Metazoa

In Spiral Cleavage, however, the third and fourth cleavage planes are oblique to the polar axis and the resulting blastomeres do not lie on top of one another but above the furrows between the cells. The spindles during the third cleavage are arranged in the form of a spiral, therefore, the name spiral cleavage. This type of cleavage is seen in all invertebrate except the echinoderms (i.e. in annelids, molluscs, arthropods nemertenes and polyclad planarians).

159_Spiral Cleavage - Metazoa.png

                                              Figure: Spiral cleavage showing transition from 4 to 8 to 16 cell stage

Spirally cleaving embryos are said to have mosaic or determinate form of development. This means that the organ forming regions of the egg are strictly localised in the egg from the very beginning and the fate of the blastomeres is determined early. If the blastomeres are separated, each will continue to develop up to a certain time as though it was a part of the whole and give rise to defective, partial embryos. In the early embryos an unidentified cytoplasmic factor is segregated into one of the blastomeres, the mesentoblast (this is also called the '4 d' cell) which gives rise to the future mesoderm.

Posted Date: 1/15/2013 1:48:34 AM | Location : United States







Related Discussions:- Spiral cleavage - metazoa, Assignment Help, Ask Question on Spiral cleavage - metazoa, Get Answer, Expert's Help, Spiral cleavage - metazoa Discussions

Write discussion on Spiral cleavage - metazoa
Your posts are moderated
Related Questions
Vitamin- D deficiency Animals obtain vitamin D either through the diet or when skin is exposed to solar radiation. The deficiency of vitamin D is associated with reduced absor

Explain briefly about the selenium Toxicity? There is a narrow margin between the beneficial and harmful intakes of selenium. The level at which selenosis occurs is not well-de

Bubble Oxygenators: These have a mixing chamber where venous blood is collected and from the bottom end micro bubbles of oxygen are passed and as they rise to the top, gas ex


Explain Human Development? Human development begins with fertilization, and continues throughout life. Fertilization occurs when two sex cells, a sperm cell and an egg cell, jo

Subphylum Sarcodiha Pseudopodia typically present; flagella present in developmental stages of some species; free living or parasitic. Superclass - Rhizopoda Loc

Food Which can be Taken in Plenty and Food to be Avoided Lastly, in the context of changing the diet, we should know the foods to be avoided and the food to be taken in plenty

What are the digestive functions of the liver? Besides making bile for release in the duodenum, the liver has other digestive functions. The venous network that absorbs nutr

EGG S OF EUTHERIA This egg is small & round. The dimeter of human egg is 0.1 mm. It has very little amount of yolk but they are also as alecithal egg. The egg is covered

a) What is biological magnification? b) Describe how DDT as a water pollutant undergoes biological magnification?