Abstract
Complete mitochondrial genome sequences are now available for 126 metazoans (see Boore 1999 ; Mitochondrial Genomics link at http://www.jgi.doe.gov), but the taxonomic representation is highly biased toward sampling of Arthropoda, Mollusca, Echinodermata, and especially Chordata. With few exceptions (see Wolstenholme 1992 ; Boore 1999 ), these are circular DNA molecules, about 16 kb in size, and they encode the same set of 37 genes. A variety of nonstandard names are sometimes used for animal mitochondrial genes (see Boore [1999] for gene nomenclature and a table of synonyms).