Sealife guideThe marine echinoderms

The phylum of echinoderms, literally « hedgehog skin », includes 5 classes and totals around 6,000 species. The most well-known of them is undoubtedly the starfish, characterized by its star-shaped form with 5 arms, or the sea urchin with its spines.

Taxonomy

Echinoderms are divided into 5 classes:

the asteroids. This class includes the most well-known echinoderms, the starfish.
the crinoids. This class includes sea lilies and feather stars.
the echinoids. Along with the asteroids, this class includes the most famous echinoderms, the sea urchins.
the holothurians. This class includes sea cucumbers or holothurians.
the ophiuroids. This class includes brittle stars, which closely resemble starfish with their flattened body and long, thin arms. Also included in this class are gorgonocephalans.

Description

Echinoderms, as the etymology of their name suggests, are animals whose outer skin surface is covered with spines, like a hedgehog. Echinoderms are primarily characterized by:

their shape, which displays a 5-fold radial symmetry
the presence of an internal skeleton made of calcareous plates or spicules
the presence of an aquifer system, called the ambulacral system, which allows them to move and feed. The aquifer system is essentially a hydraulic system that enables the movement of suckers.

Range

Echinoderms can be found throughout all the oceans and seas across the globe, at all latitudes and depths, even at very great depths.

Habitat

A red starfish under a rocky overhang

Echinoderms are sedentary and benthic animals, meaning they live resting on the seafloor. Echinoderms can be found on all types of substrates. All echinoderms are mobile, with the exception of crinoids, which are fixed to a substrate.

Diet

The diet of echinoderms is very varied depending on the species: decomposing organic matter, mollusks, …

The presence of spines in echinoderms keeps many potential predators at bay due to their size. Ultimately, echinoderms are preyed upon by very few predators.

Reproduction

Echinoderms primarily exhibit:

sexual reproduction through the release of gametes into seawater followed by external fertilization. However, to ensure the species' survival, this requires a significant quantity !
for certain classes like starfish and brittle stars, asexual reproduction through the splitting of part of the body and regeneration of the individual from that fragment.

Tips for observing

Starfish and sea urchins are often easily observable from the beach with a mask and snorkel, but be careful with your feet !

A dried starfish on a beach littered with shell fragments !

Otherwise, take a walk on the beach and carefully observe the sand and you'll surely discover some hidden treasures of nature, like a sea urchin test or a starfish dried by the sun !

Some marine echinoderms to discover

Pineapple sea cucumber
(Thelenota ananas)

Sunflower sea star
(Pycnopodia helianthoides)

Vermillion sea star
(Mediaster aequalis)

Graeffe's sea cucumber
(Pearsonothuria graeffei)

Green Brittle Star
(Ophiarachna incrassata)

Heart urchin
(Maretia planulata)

Sea Apple
(Pseudocolochirus violaceus)

Australian sea apple
(Pseudocolochirus axiologus)

Our latestUpdates

Monday, April 7th 2025

Best things to do in Miami

A flagship city of Florida, Miami is a dream destination where paradise beaches, a vibrant Latino atmosphere and a buzzing nightlife come together. With its year-round sunshine, iconic Art Deco architecture and dynamic cultural scene, Miami has everything to captivate travelers in search of escape.

Sunday, March 23rd 2025

The plumose sea anemone

The plumose sea anemone is a key species in temperate and cold marine ecosystems. Its high adaptability, morphological diversity and reproductive strategies make it a crucial organism for understanding biological and ecological interactions in marine environments.

Saturday, March 22nd 2025

World Water Day 2025 | Save the glaciers

Glaciers are essential for drinking water, agriculture, industry, clean energy, and ecosystem preservation. However, their rapid melting threatens these vital resources, making it urgent to reduce carbon emissions and implement local strategies to protect these precious water reservoirs.

Photo of the Day

Requin baleine
(Rhincodon typus)