New nemertean diversity
Many of the larvae we have found cannot be matched to any species currently in our nemertean database. We’ve identified the larvae of 37 nemertean species (both described and undescribed species, see ID guide) but, to our surprise, 19 larvae we find cannot be matched to any known species and instead represent species previously unknown to this area (e.g. red text on our pilidiophoran phylogeny below). This is particularly intriguing because the nemertean fauna in the NE Pacific, unlike other regions of the world, is believed to be well characterized. If the nemertean fauna is so well known, why are we finding these ‘orphan’ larvae?
16S neighbor-joining phylogeny for the Pilidiophora to show species for which we've identified larvae (blue text) and orphan larvae, those for which we have yet to find adults (red text).
Each benthic adult is greatly outnumbered by their larvae, producing thousands to millions at one time. That means, the chances of finding rare or difficult to collect benthic species increases by looking for their larvae in the plankton. Previous assessments of nemertean diversity are based on accounts from adjacent geographic regions and brief sampling trips targeting adults in intertidal and shallow subtidal habitats and nemerteans can be difficult to collect. They can be quite rare, interstitial, subtidal and can readily fragment into pieces when handled. In many ways, collecting adults is more difficult than collecting their larvae and it is not unexpected that we find species in one habitat that we have yet to find in the other. An important note is that there are nine species believed to be found near our marine lab which we have yet to find as adults and for which we lack sequence data.
Thus, some orphan larvae may not be orphans at all, but may be the larvae of species currently not in our reference database. Furthermore, since species descriptions are based on adult morphology, we cannot (currently) identify the larvae of these species even if we found them by morphology alone.
What began as a project of matching adults and their larvae has turned into an assessment of diversity. Perhaps all assessments of species-level diversity should include both adult and larval life-history stages to attain the most complete perspective. In just one palaeonemertean genus (Cephalothrix), for example, there are six species where previous assessments indicate two. One species we find as larvae and adults, two species we currently only find as adults and the remaining three species we have only found as larvae in the plankton. Although more sampling is required to accumulate a complete account of which nemertean species are found on the southern Oregon coast, our attempts to identify larvae have provided us with a better estimate of how many species we expect to find.
Much of the new diversity we have found is in the form of new and undescribed species, but we have also discovered five species which are well described but previously unreported from this region. We have found species previously reported from western Russia (Gurjanovella littoralis), and several from the NW Pacific (e.g. Hubrechtella juliae). (see special note about species with apparent transpacific distributions)