Sea Urchins: All Brain and Spiky Too!

Divers tend to think of sea urchins as simple animals—spiky, slow-moving, and mostly interested in grazing on algae. But an international research team has found that sea urchins are far more complex than they look. In fact, you could say that a sea urchin’s entire body acts in a way like a brain.

sea urchin
Ecology & Science

Their study, using the purple sea urchin (Paracentrotus lividus), discovered that these animals have a highly sophisticated nervous system—one that shares organisational features with the brains of vertebrates, including humans.

Two body types

To understand how strange and fascinating this is, it helps to know something about echinoderms—the group that includes sea urchins, starfish, sea cucumbers, and brittle stars.

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Stars of the Ocean: 12 Things You Might Not Know About Sea Stars

They can have up to 40,000 feet, produce millions of offspring and eat with their stomachs outside their bodies. Sounds like something from a sci-fi film? You probably see them on every dive you make! Christian Skauge and Peter Symes provide 12 intriguing insights into sea stars.

Words:
Christian Skate and Peter Symes
Images:
Christian Skauge
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Ecology & Science

Sea stars (or starfish—but they are not fish) are a common sight for divers, as they occur in all the world’s oceans, from tropical reefs to the polar seabed. But how much do you know about these slow-moving predators?

They can have between five and 30 arms, arranged in radial symmetry, and they lack blood, a brain, a heart and other vital organs. Yet they have conquered the world’s oceans. Here are some interesting facts about starfish:

Transglobal Spread of a Sea Urchin Parasite

Researchers at the University of South Florida have made a concerning discovery: a marine parasite known for devastating sea urchins in the Caribbean and Florida in 2022 has now been found afflicting sea urchins in the Sea of Oman, over 7,000 miles away. This single-celled organism, identified as a ciliate, has caused alarm among scientists who fear it may lead to a pandemic for sea urchins.

Long-spined sea urchins
Ecology & Science

The study identified the parasite that devastated 95 percent of long-spined sea urchins in affected areas in the Caribbean Sea two years ago. It burrows into the tissue of the sea urchins and triggers abnormal behaviour. The urchins droop and lose their ability to control their tube feet, which are crucial for movement. They lose their spines, then tissue necrosis sets in, leading to the death of the sea urchins.

Brittle Stars Can Learn Without a Brain

Although a brittle star does not have a brain, scientists have discovered that they are capable of learning by association.

Ecology & Science

Instead of a brain or eyes, brittle stars have nerve cords that run down each of their five arms, which join to form a nerve ring near the mouth. 

Nonetheless, according to a recent study, they possess the ability to learn by association, which involves making an association with different stimuli via a process called classical conditioning (like Pavlov’s dogs or us learning not to touch a pot of boiling water after we had been scalded before.

Sea urchins see with their whole body

Study reveals that spiny invertebrates utilize their feet as retinas. From the ends of their "feet" to the tips of their spines, sea urchins may utilize their bodies as one big eye.

Sea urchins move slowly, crawling with tube feet, and also propel themselves with their spines
Ecology & Science

According to a study that appeared in the Journal Proceedings of the National Academy of Sciences, new research has indicated that sea urchins may use the entire surfaces of their bodies—from the ends of their "feet" to the tips of their spines—as huge eyes. Scientists have long known that marine invertebrates react to light without any obvious eye-like structures, raising the question of how the animals see.

Sea Urchin Could Help Cure Diseases

Researchers found that humans and sea urchins share a lot of the same biology

Ecology & Science

A purple sea urchin has 70 percent of its genes in common with humans, including genes associated with such diseases as Huntington’s, Parkinson’s, Alzheimer’s and muscular dystrophy.

There are roughly 100 human disease genes in the sea urchin genome.

Researchers said they believe similarities in the genes of sea urchins could one day help them better understand how the human immune system works.

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Fantastic Feather Stars and the Creatures Within

Most divers take a quick look at the shapes and varieties of feather stars, but usually pass on by, in search of other interesting subject matter. However, there is more to them than meets the eye!

Words:
Steve Rosenberg
Images:
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Ecology & Science

Crinoids, or "feather stars" as they are commonly known to the scuba diving community, are echinoderms, members of the phylum Echinodermata, meaning "spiny skin," which includes many well-known species like sea stars, sea urchins and brittle stars. 

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Sea Cucumbers In Peril

Sea Cucumbers are a group of marine species belonging to the Class Holothuroidea. They are characterised by fleshy, elongated bodies, covered in numerous projections known as papillae. When disturbed, many species eject an effluvium of sticky, white threads designed to distract predators, and if removed from the marine environment, they quickly become foul smelling—not your ideal culinary ingredient, one might think. Yet the market for sea cucumber is booming, so much so that several species have seen significant population crashes.

Words:
Christophe Mason-Parker
Images:
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Ecology & Science

As with many marine species, it is the Asian market that is driving the trade, with Hong Kong and China the main hubs. Sea cucumbers have traditionally been harvested throughout their range and have long been considered a delicacy in numerous countries. However, in recent years the rise of an affluent middle class in China has led to a surge in demand, in part due to the animals’ popularity as a food source, but also as a result of its association with male virility in Chinese folk medicine.

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