Final answer:
Deuterostomia is a monophyletic group of organisms because all deuterostomes are descended from a common ancestor. The statement suggesting Deuterostomia is polyphyletic is false as it contradicts the accepted phylogenetic tree, where deuterostomes form a distinct and unified clade.
Step-by-step explanation:
The term 'Deuterostomia' refers to a major subgroup of the animal kingdom, which includes phyla such as Echinodermata and Chordata. These organisms are characterized by their embryonic development; the first opening that forms during their embryogenesis becomes the anus, while the mouth forms secondarily. As for their phylogenetic classification, the Deuterostomia is considered to be a monophyletic group, meaning they consist of all and only the descendants of a single common ancestor, which is clear from studying the modern phylogenetic tree of animals.
Considering the provided information and accepted scientific consensus, the statement under consideration is false. Deuterostomes are not a polyphyletic group, but rather a monophyletic one, as they share a single ancestor from which all members of the group have descended.
In regard to the monophyletic nature of other groups like lophotrochozoans, it is also important to recognize that molecular data, such as nucleic acid and protein analysis from mitochondrial DNA, nuclear DNA, rRNA, and certain cellular proteins, have greatly refined our understanding of animal phylogeny. These insights have led to the reclassification of certain groups, helping scientists to more accurately determine evolutionary relationships.