Phylogeny and diversification of bryozoans

Although only a small fraction of the estimated 6000 extant bryozoan species has been analysed in a molecular phylogenetic context, the resultant trees have increased our understanding of the interrelationships between major bryozoan groups, as well as between bryozoans and other metazoan phyla. Molecular systematic analyses have failed to recover the L ophophorata as a monophyletic clade until recently, when phylogenomic data placed the B rachiopoda as sister to a clade formed by P horonida +  B ryozoa. Among bryozoans, class P hylactolaemata has been shown to be the sister group of G ymnolaemata +  S tenolaemata, corroborating earlier anatomical inferences. Despite persistent claims, there are no unequivocal bryozoans of C ambrian age: the oldest bryozoans are stenolaemates from the T remadocian of C hina. Stenolaemates underwent a major radiation during the O rdovician, but the relationships between the six orders involved are poorly understood, mostly because the simple and plastic skeletons of stenolaemates make phylogenetic analyses difficult. Bryozoans were hard‐hit by the mass extinction/s in the late P ermian and it was not until the M iddle J urassic that they began to rediversify, initially through the cyclostome stenolaemates. The most successful post‐ P alaeozoic order ( C heilostomata) evolved a calcareous skeleton de novo from a soft‐bodied ancestor in the L ate J urassic, maintained a low diversity until the mid‐ C retaceous and then began to radiate explosively. A remarkable range of morphological structures in the form of highly modified zooidal polymorphs, or non‐zooidal or intrazooidal modular elements, is postulated to have evolved repeatedly in this group. Crucially, many of these structures have been linked to micropredator protection and can be interpreted as key traits linked to the diversification of cheilostomes.