Sponges and ctenophores have both been proposed as basal metazoans. Which of the following types of data support the idea that sponges are the basal group?
A) sequences of cadherin genes, cleavage type, structure of collar cells, and bilateral symmetry of adults
B) sequences of collagen genes, bilateral symmetry of adults, cleavage type, and fossil steroids
C) fossil steroids, molecular clock, lack of tissues in sponges, and structure of collar cells
D) structure of collar cells, bilateral symmetry of larvae, sequences of cadherin genes, and molecular clock

Question

Quizplus · Accepted Answer

Fossil steroids support sponges as the basal group, as they have been found in ancient sponge fossils. The lack of tissues in sponges also suggests they are the basal group, as they have a simpler body plan than other metazoans. Additionally, molecular clock analysis has suggested that sponges diverged from the rest of the metazoans earlier than ctenophores. The structure of collar cells is a characteristic unique to sponges and is not shared by ctenophores, so this also supports sponges as the basal group.

Sponges and Ctenophores Have Both Been Proposed as Basal Metazoans