Contribution to a conundrum: ecology, life history, biogeography, and taxonomy of the marine triclad Micropharynx parasitica (Platyhelminthes, Tricladida, Maricola)

The paper documents the anatomy of specimens of the marine triclad Micropharynx parasitica found in experimental woodblocks at depths of ∼1600 m from the NE Pacific and compares it to that of North Atlantic specimens of the species. North Atlantic specimens of M. parasitica are known only as ectoparasites of four species of skate, while the deep-sea population in the NE Pacific concerns free-living animals. Absence of eyes and body pigmentation in M. parasitica may be related to the deep-sea habitat instead of its association with skates. The fact that M. parasitica also occurs freely on the bottom of the ocean and apparently is able to survive without host species stimulated the authors to develop some hypotheses on the conundrum of its reproductive biology and its potential dispersal between such separate ocean basins. It may be the case that skates pick up free-living Micropharynx when the fishes deposit their egg cases on the sea floor and that the triclads deposit their cocoons on suitable substrates on the bottom of the ocean and do not attach the capsules onto their host species. Perhaps a species of skate functions for Micropharynx as a means of transport between the two ocean basins.