Acquisition of polymorphism in the chordate doliolids.

This article focuses on polymorphism in doliolids, a group of polymorphic chordates that deploy a single genome to produce multiple, morphologically distinct zooids within a colony. It reviews doliolid anatomy, development, taxonomy, ecology, and life history, emphasizing their complex life cycle involving four distinct adult morphs produced both sexually and asexually. The article situates doliolids within the broader context of polymorphism in marine invertebrates and chordates, comparing them to related thaliaceans such as salps and pyrosomes, and highlights the genetic and developmental mechanisms underlying isogenic polymorphism. It also outlines current knowledge gaps and proposes genomic and transcriptomic approaches, including single-cell RNA sequencing, to investigate the gene regulatory networks and evolutionary origins of polymorphism in doliolids and their relatives.