Meeting Abstract
Globally distributed pycnogonids, sea spiders, are a speciose chelicerate clade with 10 putative extant families. There is general agreement concerning both morphology and molecular data that sea spiders are within chelicerate Arthropods. Evolutionary patterns within Pycnogonida, particularly between families, remain unresolved due to unique morphological traits and highly reduced forms. To date, the relationships between pycnogonid clades is poorly understood and a consensus on phylogeny within the group is lacking. There have been two previous studies, which produced contrasting topologies for interrelationships between pycnogonid families. One study used morphological characteristics and six molecular loci, whereas the other was based solely on 18S rRNA sequence data. To further resolve evolutionary relationships between major groups of sea spiders, we sequenced 13 mitochondrial genomes, representing most recognized sea spider families to reconstruct phylogenetic relationships. This effort included 10 groups not previously sequenced and greatly increased the available mtDNA genome data for pycnogonids. Bayesian inference based on amino acid sequences of protein coding genes indicated that all recognized families with more than one individual represented were monophyletic. The order of protein coding genes is consistent between all sea spider mitogenomes except for Nymphon gracile. Rearrangement is more common in tRNA coding sequences and occurs in six individuals from for families in this dataset. Monophyly of all individuals from the same family and high posterior probabilities for all clades support the use of mitochondrial genomes for detection of sea spider phylogenetic position at the family level.
