It looks like  a species of Sagartia.

Thank you Jackson. Hope that Sagartia will have short tentacles!

I agree, it is certainly a cerianthus species. The shrimp is a Periclimenes species, many members of this genus live in symbiosis with sea anemones.

Thank you svoboda and mallefet

The pic is a cerianthus species and you can see under the last cycle of tentacles the tube of secretion that is builded by ptychocistes. These last are a kind of nematocysts. 

Probably Cerianthus sp.

Thank you Abhijit and Zamponi

Sir this is not a sea anemone...it is Cerianthus sp.

Thank you Arti

I agree Cerianthus

Thank you Raymond sir

It looks like a Ceriantharia specimen, with their long and thin marginal tentacles and a fewer shorter and thicker ones encircling the mouth!

Thank you very much Priscilla for your detailed explanation

You are welcome!