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In January, for example, researchers found corals, sponges and even giant sea spiders some 750 feet under the waves — all suddenly unearthed when a glacier broke free during a Schmidt Ocean Institute voyage.

The reproduction of giant sea spiders in Antarctica has been largely unknown to researchers for more than 140 years, until now.

Most notable among them was Charles Wyville Thomson, a Scotsman who in the 1860s hauled up glass sponges, sea spiders, and other curiosities—thus debunking a theory that the deep ocean was lifeless.

An unprotected clutch would prove an easy snack for predators like starfish, polychaete worms and sea spiders, Dr. Cheng said.

The results showed which body parts evolved when, and revealed that the ancestors of modern sea spiders are much older and hardier than previously thought.