and from Bermuda (Rhabdopleura normani). Both of these species are dioecious, with the fertilised egg hatching to produce a free-swimming ciliated larva. Despite the close relationship between the two groups, the larva does not resemble that of the acorn worms; they are "planula-like". Eventually, the larva settles onto the substrate and metamorphoses to an adult. Alternatively, they also reproduce asexually by budding to create a new colony. Evolution Paleontology The earliest pterobranchs, including Yuknessia and Galeaplumosus, are known from mid-Cambrian Lagerstätten. Earlier small carbonaceous fossils are known from the Buen Formation. Taxonomy Comparison of 18S ribosomal RNA sequences indicated that pterobranchs are closely related to enteropneust hemichordates. Class Pterobranchia Lankester 1877 Subclass Cephalodiscida Fowler 1892 stat. nov. Order Cephalodiscida Fowler 1892 Subclass Graptolithina Bronn 1849 Order ?†Camaroidea Kozlowski 1928 sensu Kozlowski 1949 Order ?†Crustoidea Bulman 1970 Order ?†Dithecoidea Obut, 1960 Order ?†Tuboidea Kozlowski 1938 sensu Kozlowsk 1949 Order Rhabdopleurida Fowler 1892 sensu Beklemishev 1951 Clade †Eugraptolithina Mitchell et al., 2013 Order †Dendroidea Nicholson 1872 Order †Graptoloidea Maletz, Carlucci and Mitchell 2009 Genomics Genetic code The two pterobranch taxa Rhabdopleura compacta and Cephalodiscus use alternative genetic codes in their mitochondrial genome. References External links Cameron, Christopher B. (2016). A comprehensive list of extant hemichordate species with links to images Swalla Billie J. (2007). Class Pterobranchia