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Home › Sea Life › Marine › Invertebrates › Echinoderm › Urchin › Flower Urchin

Interesting Facts about Flower Sea Urchins

[Flower Urchin Phylum: Echinodermata] [Class: Echinoidea] [Order: Camarodonta] [Family: Toxopneustidae]

Only a few of the 950 sea urchin species are venomous. Even so, the poisonous urchins have potent defences and they're capable of delivering a painful sting.

Check out these little-known facts about the flower urchin (Toxopneustes pileolus), including where they are found, and why they are regarded as the most dangerous sea urchin in the world.

Global Range and Habitat of Flower Urchins

Most of the globular sea urchins thrive in the warm waters of the Indo-Pacific regions, especially:

• Tropical and subtropical ecosystems (e.g. Caribbean Sea, Philippines, Thailand, and northern Australia).
• The Red Sea and East Africa (including Madagascar and the Seychelles)
• Near the rocky coastal shores of most temperate zones (e.g. California, Japan, and the Mediterranean Sea).

But the flower urchin is most abundant in the Indo-West Pacific (IWP).

Common habitats of sea urchin species are seagrass beds, kelp forests, or rocky substrates found at the intertidal zones where herbivores can graze on different types of algae.

It is not uncommon to find some members of the sea urchin phylum in abyssal deep polar seas at depths around 5,000 metres.

Yet, the flower urchin (Toxopneustes pileolus) is most commonly found in shallow marine environments, typically between three (3) and ninety (90) metres (300 feet).

Fun Fact: There's no shortage of funny fish names, and the flower urchin classification "poison breath" contains a few more, including the flower tip urchin, the trumpet sea urchin, poison claw urchin, and the felt cap sea urchin.

Flower Urchin Characteristics

Urchins have radial symmetry and a rounded internal shell (excluding heart urchins and sea potatoes). The shell (called a "test") is made of fused calcareous plates that are covered in 'movable spines' of various sizes.

Adult flower urchins also have a rounded shape with pink coloured concentric bands. They can grow up to twenty (20) centimetres in diameter (8 inches).

However, the main feature that makes flower urchins unique is their potent sting. Their spines are relatively short, and most of them are hidden by large flower-like pink, white, and yellow appendages, called "pedicellariae" (with several petals in each one).

They often bury themselves in the sand or use debris and shell hash collected from the ocean floor to get some protection from the sun.

Here's the thing:

The flower urchin has "pincer-like" appendages and sensory hairs hidden within the flowers.

Known as pedicellariae in echinoderms, they form a natural defence mechanism and a fierce venom delivery system.

The active chemical in flower urchin venom is in fact a glycoprotein called "Contractin A".

Contact with this "clinging" venom often causes severe pain, muscle paralysis, breathing difficulties, shock symptoms, and even potentially life-threatening situations in extreme cases.

In 2014, the Guinness Book of Records officially designated the flower urchin (Toxopneustes pileolus) as the most dangerous sea urchin in the world.

Ecological Role Helps regulate algal growth on reefs. Provides shelter for small organisms within its spines and pedicellariae. Preyed upon cautiously by certain fish and invertebrates that can handle its defenses.

Pro Tip: Our diving injuries section contains expert advice about sea urchin spine treatment with tips for avoiding marine life envenomation.

What Do Flower Urchins Eat?

Even though sea urchin species are mostly herbivorous grazers, many will supplement their daily diet with other food sources, depending on their habitat.

Hence, being a typical detritivore, many of the essential nutriments for the flower sea urchin may also include:

• Biofilm (thin slimy bacteria)
• Detritus (e.g., dead or decaying fish carcass)
• Filamentous and turf algae
• Seagrass
• Sessile invertebrates (such as bryozoans, sea sponges, soft corals)

Interesting Fact: The feeding method occurs through the use of a 5-toothed jaw mechanism known as Aristotle's lantern. Urchins use it to bite or scrape algae and coral polyps, and then guide the food to their mouth via feet-like tubular projections.

Flower Sea Urchin Reproduction

From the age of two (2) sea urchins start to become sexually mature and reproduce sexually. Most echinodermata species have separate sexes (male and female individuals).

The hard skeleton contains five gonads for males to produce sperm. Females produce eggs that have a fertilisation envelope to block multiple sperms.

Key takeaways:

Following a natural trigger for spawning season, such as a rise in water temperature, sexual reproduction results in external fertilisation when eggs and sperm are released into the open ocean.

After fertilisation, the embryos start to develop into planktonic triangular shaped larvae (called pluteus). They drift with the water currents for several weeks or months before they eventually settle on the ocean floor and transform into juvenile sea urchins.

Flower Urchin Predators and Threats

The ecological role of ocean urchins is an important one. Still, even though aquatic herbivores help to control algal growth, an overpopulation of sea urchins may also cause overgrazing.

In turn, this may reduce biodiversity and lead to rocky coral reefs being stripped of filamentous algae and kelp - a phenomenon known as "urchin barrens".

But wait - there's more:

Sea urchins face a number of natural predators as well as some human-driven threats. For example, fish families (especially triggerfishes, porcupinefish, and wrasses), sea stars (starfish), sea otters, and most crab species feed on sea urchins.

For humans, the edible part of a flower urchin is the gonads (reproductive organs called "uni"), harvested in East Asia, Southeast Asia, and the Pacific Islands.

All that being said, some of the worst human-induced threats to the long term survival of sea urchins include:

• Climate change (resulting in varying degrees of coral bleaching).
• Coral reef destruction (such as from coastal development, scuba diving tourism, and dynamite fishing)
• Underwater garbage pollution.
• Overfishing (particularly in countries where ocean urchins are considered as being a culinary delicacy, such as Europe and Japan.

One key reason why the flower urchin is not endangered is due to the indirect protection acquired through marine protected areas (MPAs) and reef conservation initiatives, particularly across the Indo-Pacific region.

Interesting Fact: In 1999, the IUCN Red List of Threatened Species assessed the conservation status of many sea urchin families as being of "Least Concern" (LC). However, they list the European Edible Sea Urchin (Echinus esculentus) as "Near Threatened" (NT).

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