The icy Antarctic waters contain a particularly diverse and vibrant range of sea spiders, marine arthropods that grow as large as dinner plates and use their tapered legs to breathe and digest. Researchers fear these creatures (such as the giant Antarctic sea spider Colossendeis megalonyx, pictured above) may suffer as the oceans get warmer and more acidic, but an international collaboration has shown that modern sea spiders come from a long line of faithful survivors.
In the study, the scientists genetically sequenced all living sea spider families (comprising 89 species, all distantly related to terrestrial spiders) to create the first complete family tree. They also incorporated information from ancient fossils.
The results showed which parts of the body evolved when and revealed that the ancestors of modern sea spiders are much older and more resilient than previously thought. This group has thrived and diversified for nearly 500 million years, the team reports this month Molecular biology and evolution. Nonetheless, the dramatic changes in ocean temperature and chemistry that accompanied the mass extinction of the late Permian, which wiped out nearly all marine life.
What Makes Sea Spiders So Hardy? The answer remains unclear; it helps that they are not dependent on calcified armor like clams and oysters, which dissolve in acidic water. But only time will tell how today’s gruesome aquatic crawlers will fare against today’s challenges, such as microplastics, oil spills and habitat destruction.