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Home › Sea Life › Marine Species › Invertebrates › Echinodermata › Crinoid

Fun and Interesting Facts about Crinoids

[Crinoid Phylum: Echinodermata] [Subphylum: Crinozoa] [Classification: Crinoidea]

The phylum Echinodermata is a group made up with various creatures that have "spiny skin" and radial symmetry displayed in their body shapes.

This section contains all the key facts about crinoid marine animals, including where they still exist, what they eat, and how their reproductive strategies differ from other echinoderms.

Crinoid Geographic Distribution and Habitat

The most impressive facts about echinoderms relate to the prehistoric geologic ranges in time and space.

For instance...

Some of the crinoid species first appeared on the planet Earth around 480 million years ago (a phase known as the Ordovician period).

Today, the worldwide distribution of crinoid animals remains immense.

Even though they still exist in polar seas, the best places to find them are the warm, shallow, oxygenated waters of the tropics.

Nowadays, modern crinoids (class Crinoidea) include two distinct members. Adult crinoids can either be sessile and attached to the sea floor (such as the stalked "flower-like" sea lilies), or they can be free-swimming (e.g., stalkless feather stars).

The present-day habitats of sea lilies are most common in extreme depths, often approaching 9,000 metres (close to 30,000 feet below sea level).

Whereas, the unstalked species of crinoids (feather stars) thrive best around shallow tropical and subtropical coral reefs, especially the Indo-West Pacific (IWP) region.

Interesting Fact: Despite being closely related to crinoids (class Crinoidea), blastoids (class Blastoidea) are one of the extinct examples of echinoderms. Blastoids also anchored themselves to the seafloor with a stalk and their body was also made of calcium carbonate interlocking plates.

Key Characteristics of Crinoids

In ancient times, crinoids dominated the shallow seas. Today, with the exception of feather stars that thrive near modern healthy coral reefs, crinoids are mostly deep-water specialists.

Like almost all echinoderms, radial symmetry is usually five-fold (pentaradial) and the most notable feature. The organs are located in the central part of the cup-shaped body (calyx) and made of calcium carbonate ossicles.

By and large, crinoids have five (5) long and feathery arms (sometimes branched into 10 or more) that contain side branches (pinnules) used in filter feeding.

Unlike most echinoderms, the mouth and the anus are both located on the oral side (upper surface) of the calyx.

But wait - there's more:

Crinoids use their tube feet and ambulacral grooves to move food particles to the mouth.

They also have a water vascular system (hydraulic network of canals) to help with circulation and movement.

The sea lily stem is a segmented column (stacked ossicles) that anchors them to the ocean floor.

Whereas, the cirri holdfasts found in feather stars and more like grasping appendages that allow them to cling to solid objects, such as coral bommies, sea sponges, or rocks.

In general, stalked crinoids are fixed to a substrate, even though research suggests some sea lily species are able to detach themselves in order to escape predation.

By comparison, the feather star has no stem and is a mobile marine animal that uses undulating movements with arms to swim, perch on coral heads, or crawl along the seabed.

Crinoids size range varies according to the classification. Still, the average size ranges between a few millimetres seen in some crinoid fossils, and even up to one (1) metre (3 feet) in some of the 600 surviving crinoid species (estimated).

Fun Fact: Some of the fossil giants towered for several metres above the seafloor. However, the modern marine forms have a crown that can span anywhere between two and thirty centimetres.

Types of Crinoids Species

What Do Crinoids Eat?

Unlike many of the predatory marine invertebrates, crinoids are passive suspension feeders. So, they use mucus-coated tube feet and feathery arms to capture plankton, zooplankton, and organic detritus matter from the water column.

How Do Crinoids Reproduce?

Crinoid reproductive strategies occur with separate sexes (male and female) usually after a natural trigger for spawning season, such as a rise in water temperature.

Sexual reproduction results from external fertilisation when eggs and sperm are released from specialised pinnules into the open ocean.

After fertilisation takes place, free-swimming crinoid larvae drift with water currents until they eventually settle on the ocean floor and metamorphose into stalked juvenile crinoids.

In case you were wondering...

Some species can reproduce asexually, either through fissiparity or fragmentation, by splitting their body in half. Each separate half can regrow the missing parts (known as arm regrowth).

So, if a crinoid loses one of its rays and the central disc, it can "clone itself" and grow the split half into a whole new creature through regeneration.

Threats and Predators

Even though the average lifespan of feather stars is about five (5) years at best, and sea lilies up to 100 years, the threats and predators that they face in the ocean are plentiful.

Nonetheless, the most prolific natural predators of crinoids are large fishes, especially butterflyfish (Chaetodontidae), wrasses, and triggerfish (Balistidae).

Plus, the crinoid species also fall prey to sea snails, sea stars, and some marine crustaceans, such as large crabs, lobsters, and saltwater shrimp.

Nonetheless, some of the worst human-induced threats to the long term survival of marine invertebrate crinoids include:

• Climate change (resulting in varying degrees of coral bleaching).
• Coastal habitat degradation and destruction.
• Underwater garbage pollution.
• Deep-sea impacts, such as from seabed mining and trawling.

Important: The IUCN Red List of Threatened Species assessed the conservation status of most echinoderms as being of "Least Concern" (LC).

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