Answer:
Gills
Explanation:
In order to remove oxygen from the water, they rely on special organs called "gills." Gills are feathery organs full of blood vessels. A fish breathes by taking water into its mouth and forcing it out through the gill passages.
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How Do Fish Breathe 
 
        
                    
             
        
        
        
No but they are considered protected
        
             
        
        
        
So, we know that a metamorphic rock is either an igneous or a sedimentary rock that are exposed to intense heat and pressure.
But when the metamorphic rock is thrusted deep underground through subduction, it will again be subjected to intense heat. This can cause it to melt, turning it into a magma. When the magma cools down, it again becomes an igneous rock and the rock cycle continues.
 
        
             
        
        
        
The sum of all the genes in a population is referred to as the gene pool.
        
                    
             
        
        
        
The first invertebrates to show both segmentation and a complete digestive system belong to the phylum Annelida that includes earthworms, leech, sandworms, etc. 
These segmented worms have complete digestive system which is also known as tube-within a tube. These can be found in freshwater, marine water or can even be terrestrial.