Meroblastic

In the presence of a large amount of yolk in the fertilized egg cell, the cell can undergo partial, or meroblastic, cleavage. Two major types of meroblastic cleavage arediscoidalandsuperficial.

Discoidal

In discoidal cleavage, the cleavage furrows do not penetrate the yolk. The embryo forms a disc of cells, called a blastodisc, on top of the yolk. Discoidal cleavage is commonly found inmonotremes,birds,reptiles, andfishthat havetelolecithalegg cells (egg cells with the yolk concentrated at one end). The layer of cells that have incompletely divided and are in contact with the yolk are called the "syncytial layer".

I want spiral cleavage

Holoblastic

In the absence of a large concentration of yolk, four major cleavage types can be observed inisolecithalcells (cells with a small even distribution of yolk) or in mesolecithal cells (moderate amount of yolk in a gradient) –bilateral holoblastic,radialholoblastic,rotational holoblastic, andspiralholoblastic, cleavage.

Spiral

Spiral cleavage is conserved between many members of thelophotrochozoantaxa, referred to asSpiralia.[5]Most spiralians undergo equal spiral cleavage, although some undergo unequal cleavage (see below).[6]This group includesannelids,molluscs, andsipuncula. Spiral cleavage can vary between species, but generally the first two cell divisions result in four macromeres, also called blastomeres, (A, B, C, D) each representing one quadrant of the embryo.

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