Figure 7
From: How Hox genes can shed light on the place of echinoderms among the deuterostomes
Phylogenetic mapping of important changes in the evolution of the deuterostome Hox cluster. (A) Chordata. (B) Ambulacraria.Hox1 has been identified in all deuterostomes. Hox2 is present in all but asteroids and ophiuroids, suggesting that its absence, if confirmed, is a synapomorphy for the asterozoan clade. Hox3 has not been identified in pedunculate crinoids, nor in the larvacean Oikopleura. Hox4 is present in all the groups considered herein, except in the crownward clade grouping echinoids and holothuroids. Hox5 is missing in Oikopleura, possibly in comatulid crinoids, and putatively in the poorly known ophiuroids. Hox6 has not been detected in Oikopleura, pedunculate crinoids, and it is possibly also absent in comatulids, ophiuroids, and holothuroids. The domains of expression of Hox5 and perhaps Hox6 could have been shifted anteriorly in some echinoderms; the position of this apomorphy on the tree depends of the character state in Asterozoa. Hox7 and Hox8 are present in all deuterostomes except two groups of urochordates and perhaps holothuroids. Their absence in two urochordate clades suggests that loss of Hox7 and Hox8 is autapomorphic for this phylum. Hox9 and Hox10 have been identified in all chordates with the sole exception that Hox9 is missing in the urochordate Ciona[114]. In Ambulacraria, all groups have a Hox9/10 gene. Hox11, Hox12, and Hox13 are present in all chordates with the exception of Ciona, which is lacking Hox11[114], but Ambulacraria have Hox 11/13abc genes not ortholog with those of chordates [56]. Hox14 is convergent between cephalochordates and cyclostomes. Hox15 is exclusive to cephalochordates. Among the related genes of the extended Hox cluster, Mox could be present in all deuterostome clades, pending further explorations in echinoderms, with two paralogous copies found only in vertebrates. Evx is present in all metazoans, including clades as basal as cnidarians [13], but two copies exist in all chordate groups (presumed apomorphy), except in larvaceans (presumed reversion).