Ammonoids, ancestors of today's octopus, squid and cuttlefish, bobbed and jetted their way through the oceans for around 340 million years beginning long before the age of the dinosaurs. If you look at the fossil shells of ammonoids over the course of that 340 million years, you'll notice something striking—as time goes on, the wavy lines inside the shell become more and more complex, eventually becoming frilled almost like the edges of kale leaves.

Octopuses are known to sleep and to change color while they do it. Now, a study publishing March 25 in the journal iScience finds that these color changes are characteristic of two major alternating sleep states: an "active sleep" stage and a "quiet sleep" stage. The researchers say that the findings have implications for the evolution of sleep and might indicate that it's possible for octopuses to experience something akin to dreams.

Possibly the oldest cephalopods in the Earth's history stem from the Avalon Peninsula in Newfoundland (Canada) discovered by scientists from Heidelberg University. The 522-million-year-old fossils could turn out to be the first known form of these highly evolved invertebrate organisms, whose living descendants today include species such as the cuttlefish, octopus and nautilus. The find would indicate that cephalopods evolved about 30 million years earlier than has been assumed.

In jade waters off Hong Kong's eastern shoreline, scientists are thrilled to spot a cuttlefish protecting her eggs inside an artificial, 3D-printed clay seabed helping to restore the city's fragile coral reefs.

Squids have long been a source of fascination for humans, providing the stuff of legend, superstition and myth. And it's no wonder—their odd appearances and strange intelligence, their mastery of the open ocean can inspire awe in those who see them.