Which of the following combinations of phylum and description is correct? (and why?) a) Nematoda − roundworms, internal skeleton
b) Porifera − gastrovascular cavity, coelom
c) Echinodermata - radial symmetry as a larva, coelom
d) Platyhelminthes − flatworms, gastrovascular cavity, no body cavity

this is true, assuming that the allele is completely recessive and incomplete dominance is not a factor.

primary succession occurs in essentially lifeless areas regions in which the soil is incapable of sustaining life as a result of such factors as lava flows, newly formed sand dunes, or rocks left from a retreating glacier. secondary succession occurs