Gene arrangements in heteroscleromorph mt-genomes determined for this study.

Superscript number associated with each species name refers to a unique gene order marked by the same number. Species are grouped mainly by taxonomic orders. In a few cases when taxonomy of a species is inconsistent with the results of phylogenetic analyses, the species is grouped according to the latter results. Because phylogenetic analysis does not place Petromica sp. in any accepted orders of demosponges, its systematic position is marked as “???”. Protein and rRNA genes (larger boxes) are: atp6, 8–9—subunits 6, 8 and 9 of the F0 ATPase, cox1–3—cytochrome c oxidase subunits 1–3, cob—apocytochrome b (cob), nad1–6 and nad4L—NADH dehydrogenase subunits 1–6 and 4L, rns and rnl—small and large subunit rRNAs. tRNA genes (smaller boxes) are abbreviated using the one-letter amino acid code. The two arginine, isoleucine, leucine, and serine tRNA genes are differentiated by numbers with trnR(ucg) marked as R1, trnR(ucu)—as R2, trnI(gau)—as I1, trnI(cau)—as I2, trnL(uag)—as L1, trnL(uaa) as L2, trnS(ucu)—as S1, and trnS(uga)—as S2. All genes are transcribed from left to right. Genes are not drawn to scale and intergenic regions are not shown. Missing sequences are indicated by gray boxes.