Figure 4

Schematic representation of Hox gene expression in Dreissena rostriformis. Summary of Hox expression patterns together with the localization of Hox genes in the genome of selected mollusk species. (A) Hox genes in the late gastrula (left) and the late trochophore larva (right) do not follow a temporally or spatially staggered mode of expression. (B) Hox gene arrangement in mollusks. Phylogenetic tree adapted from^1,66, animal schemes modified after⁶⁷. Data from^{16,18,19,35,39,57,68}. Straight red lines indicate absence of coding sequences between individual Hox genes, dotted red lines indicate presence of non-Hox genes between Hox genes, blank space between Hox genes means that presence or absence of non-Hox genes between Hox genes remains unknown. Species for which gene expression data by in situ hybridization are available are highlighted in red. ++ marks lineages with clear spatially staggered Hox expression, + indicates prominent hints of spatial Hox expression, ( +) symbolizes weak hints of spatial expression, - indicates absence of staggered expression, ? indicates that no clear statement concerning staggered Hox expression can be made. Note that the situation in Mizuhopecten yessoensis is somewhat undecided since only few Hox genes were investigated in the gastrula stage only. Quotation marks indicate that species identity is not fully settled (G. varia, A. entalis) or that genomic and gene expression data for the identical species have been published under different species names (A. fascicularis, where gene expression data were erroneously assigned to A. crinita). a, anterior; d, dorsal; ec, ectoderm; en, endoderm; me, mesoderm; p, posterior; sf, shell field; v, ventral; asterisk, blastopore/mouth opening.