Crinoids: The Living Fossils

Crinoids: The Living Fossils

Crinoids, also known as feather stars, are some of the oldest animals living in the ocean today. They first appeared over 500 million years ago—long before the dinosaurs—and have changed very little since then. As a result, scientists often call them “living fossils.”

Although crinoids look like underwater plants, they are actually animals. You can find them in many places around the world, from shallow coral reefs to deep sea trenches and sandy bottoms. 

In this article, we’ll explore what crinoids are, how they live and move, and the amazing partnerships they have with other sea creatures—especially here in the Lembeh Strait. Let’s dive in.

A Window Into the Ancient Past

Crinoids first appeared in the fossil record over half a billion years ago, making them some of the oldest living species in the world today. They emerged during the Middle Cambrian era, around 300 million years before the arrival of dinosaurs.

More than 5,000 crinoid fossil species have been described, making them one of the most common and diverse species in the fossil record. Today, around 650 living species are known to science, and they remain abundant in a variety of marine habitats.

Over hundreds of millions of years crinoids have changed relatively little, since the simplicity of their design has been so successful. As a result, they are one of those rare examples of an organism considered to be a living fossil – a glimpse of what life was like in the ocean long before humans appeared.

Crinoids are living fossils belonging to the echinoderms group, which also includes sea stars, urchins, brittle stars, and sea cucumbers (Photo: Ross Makulec)

Biology, Appearance, and Ecology

Crinoids are related to sea stars, urchins, brittle stars, and sea cucumbers. Together, these five groups form the major branch of the animal kingdom called the echinoderms (meaning ‘spiny skin’). Members of this group have a basic five-sided symmetry and a calcareous skeleton. 

Although crinoids resemble plants (their name means ‘lily-like’) they are actually animals, complete with digestive and nervous systems. Interestingly, crinoids are older than any land plants, so you could say that terrestrial flora resemble crinoids, rather than the other way around.

Crinoids are colorful animals with small, disc-like bodies, long, feather-like arms and small, jointed legs called cirri (pronounced “siri”). They also play a crucial ecological role, by recycling nutrients on the ocean floor and providing shelter for a wide variety of fish and invertebrates.

Crinoid legs are covered in hundreds of tiny, tubular feet, which they use to catch passing morsels of food. Some crinoids also fluoresce under UV light, which makes them an excellent subject for fluoro photography  (Photo: Ross Makulec)

Eating and Moving Around 

On dives at Lembeh Resort, we often see crinoids on both reefs and sandy bottoms. They occasionally walk or swim using undulating arm movements, but are more commonly seen ‘rooted’ on reef outcrops and open bottoms, where they can filter feed in the gentle currents of the Lembeh Strait.

Their legs are covered in hundreds of tiny, tubular feet, which in turn are covered in a layer of sticky mucus. This enables them to catch passing morsels of food. Uniquely, crinoids have an internal canal system which enables them to pass food down their arms to the stomach – each of the 10 arms function like a mouth and esophagus.

When diving in Lembeh, we often see ghost pipefish around crinoids, and are amazed by how closely their camouflage mimics the appearance of feather stars (Photo: Jacob Guy)

Animal Partnerships

Crinoids are fascinating creatures in their own right, but what makes them even more interesting to us is the partnerships they have established with other marine animals. Many species use crinoids for shelter, camouflage, or even permanent residence. 

Some species have evolved to live alongside crinoids and mimic their appearance. One example is the ornate ghost pipefish, which blends perfectly into the colorful feathers of the crinoid and thereby evades predators, while also waiting in ambush for potential prey. Another is the crinoid clingfish, which uses a suction pad on the underside of its body to anchor itself on the central disc of the crinoid. 

Crinoids provide temporary shelter to many species of juvenile fish and crustaceans, while crinoid shrimp and crinoid squat lobsters live out their entire lives in the safe embrace of the crinoid’s arms. When diving in Lembeh, you’ll find that crinoids are like a mini ecosystem, where various living creatures can be discovered, observed, and photographed. 

A crinoid squat lobster, one of several invertebrate species that spend their entire lives living within feather stars (Photo: Ross Makulec)

A tiny crinoid clingfish, peeking out from the central disc of a crinoid. These creatures are an equally challenging and rewarding subject for underwater macro photography in Lembeh (Photo: Ross Makulec)

A Closer Look at Crinoids

Crinoids are fascinating creatures with an amazing history. They come in various different colors and make a great subject for creative photography. Moreover, with so many creatures – such as ghost pipefish, crinoid clingfish, and various invertebrates – making their home in and around crinoids, this makes them both the subject and the setting for some incredible macro photo opportunities.

For a closer look at crinoids, check out our Lembeh Learning Series on YouTube. Episode 2 is all about these amazing feather stars, and features footage captured on recent dives in the Lembeh Strait.