The Mitochondrial Sequences ofHeptathela hangzhouensisandOrnithoctonus huwenaReveal Unique Gene Arrangements and Atypical tRNAs.

We have sequenced the complete mitochondrial genomes of the spidersHeptathela hangzhouensisandOrnithoctonus huwena. Both genomes encode 13 protein-coding genes, 22 tRNA genes, and 2 ribosomal RNA genes.H. hangzhouensis, a species of the suborder Mesothelae and a representative of the most basal clade of Araneae, possesses a gene order identical to that ofLimulus polyphemusof Xiphosura. On the other hand,O. huwena, a representative of suborder Opisthothelae, infraorder Mygalomorphae, was found to have seven tRNA genes positioned differently from those ofLimulus. TherrnL-trnL1-nad1arrangement shared by the araneomorph families Salticidae, Nesticidae, and Linyphiidae and the mygalomorph family Theraphosidae is a putative synapomorphy joining the mygalomorph with the araneomorph. Between the two species examined, base compositions also differ significantly. The lengths of most protein-coding genes inH. hangzhouensisandO. huwenamtDNA are either identical to or slightly shorter than theirLimuluscounterparts. Usage of initiation and termination codons in these protein-coding genes seems to follow patterns conserved among most arthropod and some other metazoan mitochondrial genomes. The sequences of the 3' ends ofrrnSandrrnLin the two species are similar to those reported forLimulus, and the entire genes are shortened by about 100-250 nucleotides with respect toLimulus. The lengths of most tRNA genes from the two species are distinctly shorter than those ofLimulusand the sequences reveal unusual inferred tRNA secondary structures. Our finding provides new molecular evidence supporting that the suborder Mesothelae is basal to opisthothelids. [ABSTRACT FROM AUTHOR]