Hi

Colobocentrotus atratus, commonly known as the helmet urchin or shingle urchin, belongs to the sea urchin family Echinometridae. In Hawaii, it is referred to as hāʻukeʻuke. This species is found on wave-swept intertidal shores in the Indo-West Pacific, particularly along the shores of Hawaii. The urchin exhibits a deep maroon color and has a dome-shaped structure resembling a limpet. While it can reach the size of a softball, it typically remains smaller. The upper surface showcases a mosaic of tiny polygonal plates formed from modified spines, creating a smooth texture.

Shingles Urchins

( Colobocentrotus atratus )

Colobocentrotus atratus by kueda via Inaturalist 

Scientific classification
Kingdom	Animalia
Phylum:	Echinodermata
Class:	Echinoidea
Order:	Echinoida
Family:	Echinometridae
Genus:	Colobocentrotus
Species:	C. atratus

Colobocentrotus atratus, commonly known as the helmet urchin or shingle urchin, belongs to the sea urchin family Echinometridae. In Hawaii, it is referred to as hāʻukeʻuke. This species is found on wave-swept intertidal shores in the Indo-West Pacific, particularly along the shores of Hawaii.

The urchin exhibits a deep maroon color and has a dome-shaped structure resembling a limpet. While it can reach the size of a softball, it typically remains smaller. The upper surface showcases a mosaic of tiny polygonal plates formed from modified spines, creating a smooth texture. Surrounding this is a ring of large, flattened modified spines. On the underside, there's another ring of smaller flattened spines and a significant number of tube feet. Toxicity of the urchin is currently unknown.

Distribution and Habitat

Range map of Colobocentrotus atratus from iNaturalist.org, CC BY-NC 4.0.

Shingle urchins are commonly found in the Indo-West Pacific, particularly along the shores of Hawaii, inhabiting wave-swept intertidal areas. They are usually located on substrates fully exposed to waves and their associated abrasive effects, often in groups.

Diet

Coralline algae by FalsePerc via Wikimedia commons

Shingle urchins are omnivores and are known to feed on periwinkles,

×

Periwinkles

The ordinary periwinkle or winkle (Littorina littorea) is a type of small, edible whelk or sea snail. This marine gastropod mollusk possesses gills and an operculum and belongs to the Littorinidae family, commonly known as periwinkles. It thrives in intertidal zones, displaying a sturdy, often dark, and occasionally banded shell. Originally found along the rocky shores of the northeastern Atlantic Ocean, it has also been introduced to the northwestern Atlantic.

Indigenous to the northeastern coasts, including areas like northern Spain, France, Great Britain, Ireland, Scandinavia, Russia, and Nigeria, L. littorea reproduces annually through oviparous means. The internal fertilization of egg capsules results in their release directly into the sea, leading to a planktotrophic larval development period lasting four to seven weeks.

other urchins and coralline algae. 

Biology

Closeup of C. atratus tube feet by  Damon Tighe  via Inaturalist

In a comparative test (link) between shingle urchins and other species like Echinometra, shingle urchins demonstrated exceptional resistance to being washed away by moving water. Their shape, flattened spines, and strong tube feet adhesion made them three times as resistant. This adaptation allows them to thrive on wave-battered shorelines.

In the test, shingle urchins showcased impressive attachment force, resisting dislodgment at water velocities of up to 27.5 m/s, outperforming typical spiny echinoids. The shape offsets shear force on tube feet, spreading the energy load evenly.

Their ability to inhabit extreme water velocities is attributed to its high number of tube feet rather than specific morphology. Adaptive notions for its shape include streamlined morphology to lessen hydrodynamic forces, flattened spines to reduce breakage, and an ideal morphology for retaining extra water, crucial to resist heat and dessication stress at low tide.

---

References

• ChrisM. (2008, April 21). "Holding on in a rough world: Colobocentrotus atratus-the shingle urchin!!".The Echinoblog. Retrieved on November 30, 2023, from
  http://echinoblog.blogspot.com/2008/04/holding-on-in-rough-world.html?m=1.
   

• Santos, Romana; Flammang, Patrick (2008). "Estimation of the attachment strength of the shingle sea urchin, Colobocentrotus atratus, and comparison with three sympatric echinoids". Marine Biology. 154: 37–49. doi:10.1007/s00227-007-0895-6. Retrived on November 30, 2023, from
https://link.springer.com/article/10.1007/s00227-007-0895-6.

   

• Denny, M; Gaylord, B (1996). "Why the urchin lost its spines: Hydrodynamic forces and survivorship in three echinoids". The Journal of Experimental Biology. 199 (Pt 3): 717–29. PMID 9318472. Retrived on November 30, 2023, from
https://pubmed.ncbi.nlm.nih.gov/9318472/.