About the Cover
That’s not an 18th-century writer’s quill on the cover or even a gorgeous deep water plant, but a sea pen — a creature belonging to the Cnidaria family, which includes jellyfish, coral and sea anemone.
The earliest fossils date this colonial creature to the Cambrian period — some 541 million years before being featured on our book — and the pens are still thriving today in both coastal and deep temperate and tropical waters.
You can observe the soft colorful stalks of the pens lodged in the seafloor, often grouped like an underwater garden of feathers. And just as you glance at an application on your phone and take in one interface that is actually made of many working features, the sea pen isn’t one creature at all, but a colony of creatures.
The main stem is one polyp — the first to take root — that then supports many other smaller polyps whose tentacles make up the fringes we see. And like the various aspects of the seamless interfaces made with SwiftUI, the delicate polyps are cleverly designed for different purposes to support the whole creature – intaking water, maintaining structure, eating and reproducing. The pens have been observed expanding and shrinking, articulating their frayed bodies, reacting to crabs and other touch, and even glowing.
A sea pen may be stationary, like any application anchored within the confines of your device. But the pens show us that with the right construction and design, you can architect something cohesive, fluid, beautiful and dynamic.