Cleavage in the jellyfish Aequorea

The hydrozoan jellyfish Aequorea spawns smallish, glassy-clear eggs. Within an hour or two of fertiliztion the zygote begins to cleave from one side of the cell. The cleavage furrow remains unilateral as it cuts through the egg; no furrow forms on the opposite side. Subsequent divisions result in a rather disorderly morula which nevertheless organizes itself into a mostly regular hollow blastula.

Aequorea are at times rather common in Friday Harbor; they're relatively large, low-domed, "fleshy" medusae with dozens of radial canals. I've never come across one smaller than a nickel, and they get to be about the size of your palm (sometimes larger), at which size many of them seem to be ripe. After catching them in daylight and keeping them overnight in jars of clean seawater, they spawn shortly after exposure to morning light (although the timing doesn't seem to be reliable).