The mermaid's purse, or what the skate can tell us about keeping eggs safe in one basket

摘要

Egg laying vertebrates with relatively small clutches of large yolked eggs (elasmobranchs, reptiles and birds) have developed a diversity of tertiary membranes to contain and protect the egg/embryo from environmental assaults. The eggs of oviparous elasmobranchs (some sharks and all skates) are left to fend for themselves in the marine environment for up to a year or longer. Once released, the egg capsule is moored to stationary objects where it must resist attacks of molluscs, bacteria, and other predatory organisms. Elasmobranchs have solved this problem quite successfully by the invention of the tough, leathery and extremely durable egg capsule, the product of a specialised region of the reproductive tract, the oviducal, shell or nidamental gland. This material is able to withstand the corrosive action of sea water for remarkably long periods, remarkable especially given that it is composed almost entirely of proteins.