Mount Holyoke College

Sea Urchin Cleavage

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This sequence was filmed by Rachel Fink, Mount Holyoke College. It appears in the video A Dozen Eggs: Time-Lapse Microscopy of Normal Development published by The Society for Developmental Biology and Sinauer Associates, Inc.

Sea urchin embryos are a favorite of developmental biologists because they are transparent and develop synchronously. This newly fertilized Lytechinus pictus zygote undergoes first mitosis and cytokinesis. Cleavage is equal and holoblastic, giving rise to the two-celled stage. Cleavage continues approximately every 30 minutes, giving rise to a 32-cell stage morula.