As someone from a land-locked state, I can neither confirm nor deny that this resembles a sea urchin shell (do they have shells?). However - this is a GREAT hide for jumping spiders! It's unusual shape gives them room to make a hammock but also peek out. 
 
Further evidence: in a market research panel, 9 out of 10 jumping spiders agreed with the statements: "I could totally molt in this" and "this hide makes me feel pretty". 
But seriously, it's just a good hide.
 
Right now I have juvenile/sub-adult size available, smaller than the pictures taken with my spiders (but let me know if you really want an large version - they're huge!).
 
(Big booty ghost not included)
 
***I make each piece by hand, and there may be human touches at times (evidence of the nontoxic glue, crooked magnet, etc). :) However, I am picky and strive to send you the best pieces! To prolong the life of your spood's perch, please try not to mist it directly! :)