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MeargleSchmeargl

Mysterious stripes on Echies

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MeargleSchmeargl

I've always wondered what the 5 radial stripes on echinoids we're and what they do. Any urchin/sand dollar experts know? :D

 

Echinoid_Sand_Dollar_Fossil_2048x.thumb.jpg.a992ea56943927ddef208302f6c2429b.jpg

Polished Echie with the "stripes".

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erose
On 7/28/2018 at 9:44 AM, Tidgy's Dad said:

I think it's because the sea-urchins are divided into five ambulacral (walking) areas and five interambulacral areas underneath, each consisting of 2 rows of plates. On the underside the ambulacra hold the tube feet and the interambulacra do not. This design continues onto the upper surface of the urchin but without the feet, though in regular urchins spines may be present in both areas. Irregular urchins have lost the spines, but retain the basic design. 

Or something. 

yeah, something like that.... Google up Echinoid Morphology for a more concise explanation &/or visit:http://www.nhm.ac.uk/our-science/data/echinoid-directory/index.html

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Tidgy's Dad
3 hours ago, Coco said:

The 5 parts of the star are called ambulacra, zones between every ambulacra are called ""interambulacral zones".

 

Pores situated on ambulacres bring out mild parts as small tubes (podia), between spines. These mild parts serve to shake the water and to bring the food up to the mouth.

 

As regards the irregular sea urchins, they didn't lose their spines, but they have "silks" on their place (small very fine and fragile spines, thickness of a lash). Sorry Adam if I didn't well understand your explanation ;)

 

Podia : http://www.snv.jussieu.fr/bmedia/oursinMDC/piedamb.html ("Piquants = spines).

 

Ambulacra / interambulacra zones : http://www.nhm.ac.uk/our-science/data/echinoid-directory/morphology/JPEG/REGULAR.JPG

 

Irregular sea urchin with "silks" : 

 

Coco

 

 

No, problem. :)

Your explanation is better than mine. 

Though I would argue that the silks are less fragile than spines. They can be pretty tough and aren't as brittle.  

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Coco

I have found a great number of recent sea urchins, regular and irregular ones, on our french coast or in La Reunion Island, and I think really silks are more breakable than spines when sea urchins are dried. For example Echinocardium, Brissus and more species ;)

 

Coco

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Tidgy's Dad
On 8/26/2018 at 1:05 PM, Coco said:

I have found a great number of recent sea urchins, regular and irregular ones, on our french coast or in La Reunion Island, and I think really silks are more breakable than spines when sea urchins are dried. For example Echinocardium, Brissus and more species ;)

 

Coco

When dried, that's probably true. 

But not when the critters are alive. 

Take your example of Echinocardium for one.

They burrow into the substrate down to about 15 cm and this is the reason they can't have long and brittle spines, the tough silks, that trap air for them to breath under the surface are more streamlined and won't break as they prefer grainy, sandy sediments rather than soft muds. ;)

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Coco

That's right ! ;)

 

Coco

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