The invertebrate phylum representing the second largest is____________?
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Answer: C. Mollusca
Explanation
Mollusca is recognized as the second largest invertebrate phylum after Arthropoda in terms of species diversity. This diverse taxonomic group includes snails, clams, squids, and octopuses inhabiting aquatic and terrestrial realms. Their widespread evolutionary success accounts for the massive number of described mollusc species. Invertebrates comprise animals lacking a vertebral column, representing the vast majority of animal species. Molluscs typically share a muscular foot, a visceral mass, and a mantle often secreting a calcium carbonate shell. Arthropods remain the largest invertebrate phylum, containing insects, arachnids, and crustaceans.
Marine ecosystems rely heavily on molluscs as key primary consumers, predators, and commercial fishery resources. Studying mollusc phylogeny helps evolutionary biologists understand complex organ system developments in invertebrates. Many mollusc species serve as crucial bioindicators monitoring environmental pollution in coastal marine waters. Porifera comprises simple aquatic sponges representing one of the most basal and ancient animal phyla. Arthropoda is the largest invertebrate phylum, surpassing Mollusca in total documented species count. Chordata is a vertebrate-dominated phylum containing animals with notochords rather than invertebrate molluscs.
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