Worms living within worms: a new endosymbiotic rhabdocoel flatworm (Umagillidae)

Describing new species of obscure invertebrates is how I get my kicks, thus I'm quite pleased with one of my most recent papers.

Huston, D.C. 2019. Collastoma esotericum (Neodalyellida: Umagillidae), a new species of sipunculan-inhabiting rhabdocoel from Queensland, Australia. Zootaxa, 4701 (6), 563-573.

http://dx.doi.org/10.11646/zootaxa.4701.6.5 

The most well-known parasitic flatworms are the highly-derived monogeneans, digeneans and cestodes, members of the platyhelminth subclade Neodermata. However, there are numerous ecto- and endosymbiotic ‘turbellarian’ flatworms scattered throughout the remaining lineages of the Platyhelminthes.

Invertebrates host a variety of endosymbiotic flatworms and these relationships are likely among the most ancient of metazoan symbioses. Echinoderms host two distinct groups of endosymbiotic flatworms, species of the families Umagillidae and Pterastericolidae. The pattern of host-association is also peculiar. The crinoid, echinoid and holothuroids host umagillids, while the asteroids host pterastericolids. There is apparently no overlap. Further, some umagillids have been reported from species of the Sipuncula (peanut-worms). The overall patterns suggests (to me at least!) multiple transitions from free-living to endoparasitism. However, none of these flatworm lineages have been studied in great detail, and there are few molecular resources for these species.

In my MS I describe a new species of the peanut-worm inhabiting umagillids. I was hoping that my molecular analyses would provide strong evidence for my above hypothesis (multiple transitions from free-living to endoparasitism), however I was only able to obtain sequences of the 18S rDNA gene as amplification of all other regions failed, despite the many different primers and cycling conditions I tried. Ultimately the results of my analyses didn't provide enough support to show this for sure just yet, but I suspect that future work will.