Lang observed that "Mittelwülste" (= anteromesial cuticular thickenings) varied among Pycnophyes calmani, P. flaveolus and P. kielensis and concluded that this character does not represent a character to distinguish different species.

Abstract (shortened): Here we present the results of sequencing and analysis of mitochondrial genomes from Echinoderes svetlanae and Pycnophyes kielensis. Their mitochondrial genomes are circular molecules approximately 15 Kbp in size. The kinorhynch mitochondrial gene sequences are highly divergent, which precludes accurate phylogenetic inference. The mitogenomes of both species encode a typical metazoan complement of 37 genes, which are all positioned on the major strand, but the gene order is distinct and unique among Ecdysozoa or animals as a whole. We predict four types of start codons for protein-coding genes in E. svetlanae and five in P. kielensis with a consensus DTD in single letter code. The mitochondrial genomes of E. svetlanae and P. kielensis encode duplicated methionine tRNA genes that display compensatory nucleotide substitutions. Two distant species of Kinorhyncha demonstrate similar patterns of gene arrangements in their mitogenomes. Both genomes have duplicated methionine tRNA genes; the duplication predates the divergence of two species. The kinorhynchs share a few features pertaining to gene order that align them with Priapulida. Gene order analysis reveals that gene arrangement specific of Priapulida may be ancestral for Scalidophora, Ecdysozoa, and even Protostomia.

The monophyly of Ecdysozoa, which comprise molting phyla, has received strong support from several lines of evidence. However, the internal relationships of Ecdysozoa are still contended. We generated expressed sequence tags from a priapulid (penis worm), a kinorhynch (mud dragon), a tardigrade (water bear) and five chelicerate taxa by 454 transcriptome sequencing. A multigene alignment was assembled from 63 taxa, which comprised after matrix optimization 24,249 amino acid positions with high data density (2.6% gaps, 19.1% missing data). Phylogenetic analyses employing various models support the monophyly of Ecdysozoa. A clade combining Priapulida and Kinorhyncha (i.e. Scalidophora) was recovered as the earliest branch among Ecdysozoa. We conclude that Cycloneuralia, a taxon erected to combine Priapulida, Kinorhyncha and Nematoda (and others), are paraphyletic. Rather Arthropoda (including Onychophora) are allied with Nematoda and Tardigrada. Within Arthropoda, we found strong support for most clades, including monophyletic Mandibulata and Pancrustacea. The phylogeny within the Euchelicerata remained largely unresolved. There is conflicting evidence on the position of tardigrades: While Bayesian and maximum likelihood analyses of only slowly evolving genes recovered Tardigrada as a sister group to Arthropoda, analyses of the full data set, and of subsets containing genes evolving at fast and intermediate rates identified a clade of Tardigrada and Nematoda. Notably, the latter topology is also supported by the analyses of indel patterns.