Meeting Abstract
Phylogeny within Nemertea has been well characterized by two multigene studies (Thollesson & Norenburg 2003, Andrade et al 2014a), whose broad consensus results were recently supported by a transcriptomics study (Andrade et al 2014b). A surprising result in both earlier studies was the placement of Carcinonemertidae as the sister-group to the suborder Distromatonemertea. Consensus understanding of carcinonemertid biology and their much-simplified anatomy – reflected in long-standing taxonomy – suggests they are highly derived within that suborder. We obtained transcriptome data for Carcinonemertes epialti and will have combined and reanalyzed it with the previous nemertean transcriptome data, to test the placement of Carcinonemertidae inferred by the previous multigene studies. Current possible hypotheses for phylogenetic placement of Carcinonemertidae with respect to Distromatonemertea are: 1) it is sister to the suborder as a) a basal lineage within it, or b) a member of the sister clade including Cratenemertidae; 2) it is a derived member of the suborder but a) its position reflects a rapid molecular clock, or b) it is an ancient surviving lineage among more basal lineages that have gone extinct. The highly reduced anatomy of carcinonemertids offers only one standard morphological feature with potential to inform these hypotheses; it is the synapomorphy for Distromatonemertea: rhynchocoel wall circular and longitudinal musculature having the state “bilayered” rather than “interwoven.” To date, histological studies for any species of Carcinonemertidae have been inconclusive but new confocal microscopy images presented here weakly support the state “bilayered.”
