Hox genes in a pentameral animal

There is renewed interest in how the different body plans of extant phyla a re related. This question has traditionally been addressed by comparisons b etween vertebrates and Drosophila. Fortunately, there is now increasing emp hasis on animals representing other phyla, Pentamerally symmetric echinoder ms are a bilaterian metazoan phylum whose members exhibit secondarily deriv ed radial symmetry. Precisely how their radially symmetric body plan origin ated from a bilaterally symmetric ancestor is unknown, however, two recent papers address this subject. Peterson et al.((1)) propose a hypothesis on e volution of the anteroposterior axis in echinoderms, and Arenas-Mena et al. ((2)) examine expression of five posterior Hox genes during development of the adult sea urchin. BioEssays 23:211-214, 2001. (C) 2001 John Wiley & Son s, Inc.