Sense Organs in Holopelagic Annelids

Project Title: Sense organs and nervous system in holopelagic polychaetes, an ultrastructural and CLSM approach

Funding Source: University

Principle Investigator: Günter Purschke and Conrad Helm, Uni. of Göttingen

Investigations on evolution, systematics, phylogeny and functional morphology are in the focus of interest. Currently these investigations are carried out on annelids, the segmented worms, and those taxa which are presumed to be closely related to them. Special emphasis is laid to the phylogenetic relationships within and validity of Lophotrochozoa.

Marine annelids commonly known as polychaetes are typically benthic organisms dwelling on or in all kinds of marine bottoms. They are only present in the water column during their reproductive phase, if at all. There are a few exceptions from this general rule one of which being Tomopteridae, a clade of predatory holopelagic annelids occurring from surface waters down to at least 3,800 m depth. As such this lifestyle is hypothesized to require special adaptations of their sensory, nervous and locomotor system. Being almost transparent and inviable in the water these animals are equipped with large eyes, several other sense organs and a highly developed nervous system. The project aims on whether there exist special adaptions correlated with the pelagic life, similarly as observed, for instance, in pelagic Alciopidae equipped with the highest differentiated eyes found to date in Annelida.

The upper photo shows an entire individual of Tomopteris helgolandica (length about 3 cm), the lower photo a close-up of the anterior end with the large pigmented eyes.