Egg mass of the Spanish dancer (Hexabranchus sanguineus) The egg mass of this nudibranch is called the sea rose and is covered by toxins that the animal accumulates from its venomous prey. (more) 7 Animals that Lay the Most Unusual Eggs Written by Manjishtha Bhattacharyya Manjishtha Bhattacharyya is an editor at Encyclopaedia Britannica. She holds a PhD in zoology from Vidyasagar University, West Bengal, and has more than seven years of experience in science communication... Manjishtha Bhattacharyya Fact-checked by Britannica Editors Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree.... Britannica Editors Last updated Mar. 30, 2026 •History Almost all animals begin life as a fertilized egg, or ovum. Females (or female-gamete-producing hermaphrodites) of most invertebrates and all vertebrates that we commonly encounter produce, and in many cases lay, eggs. These eggs as well as their coverings or cases vary remarkably in size, shape, structure, and shade. The list below takes a closer look at seven of the most unusual eggs (and egg cases) in the animal world and the creatures that produce...

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