Coral reefs are part of the marine and oceanic ecosystem that are hard and made up of calcium carbonate. Planulae is not the major structure of coral reefs.
<h3>What are coral reefs and Planulae?</h3>
Coral reefs are the hard calcium structures that are of three major types barrier, fringing and atoll.  They feed on the planktons and algae that are the small structures inhabiting them.
Planulae is a freely swimming larvae of the jellyfish and other species of Ctenophores. They are solid, flat and have cilia over their body. 
Therefore, option a. Planulae is not a structure or type of coral reef.
Learn more about coral reefs here:
brainly.com/question/2108897
 
        
             
        
        
        
At least four types of naturally occurring recombination have been identified in living organisms: (1) General or homologous recombination, (2) Illegitimate or nonhomologous recombination, (3) Site-specific recombination, and (4) replicative recombination.
        
                    
             
        
        
        
 Natural selection<span> is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations.</span>
        
                    
             
        
        
        
B. They make their own food, Position 1 because all of those animals would have jaws. B. Cellular Respiration, A. They belong to the same kingdom but different phyla.
        
             
        
        
        
Speciation<span> is the </span>evolutionary<span> process by which biological populations evolve to become distinct </span>species<span>. The biologist </span>Orator F. Cook<span> coined the term 'speciation' in 1906 for the splitting of lineages or "</span>cladogenesis," as opposed to "anagenesis<span>" or "phyletic evolution" within lineages.</span>