Meeting Abstract
The feeding capabilities of larval polyclad flatworms are poorly understood. Indirect developing flatworm larvae typically display one of two planktonic larval forms known as Götte’s or Muller’s larvae. Recent reviews of the literature suggest that Muller’s larvae typically develop as obligate feeders, while Götte’s larvae are thought to be either non-feeding or facultatively feeding. However, Muller’s larvae typically develop from larger eggs (mean ~150 µm) than Götte’s larvae (mean ~ 100 µm) and smaller eggs typically reflect lower per offspring investment and greater reliance of larvae on exogenous food. We investigated the feeding requirements of Stylochus ellipticus, a polyclad flatworm that develops from a small egg (~65 µm) into a Götte’s larva, and whose development has been previously described as non-feeding. Three types of unicellular algae were tested as potential food sources and while all three algae were ingested, only cultures reared on Rhodomonas lens developed to metamorphosis. We subsequently tested the effectiveness of three different levels of R. lens as a food supply and found that juveniles were only regularly observed when provided algae at high levels (50,000 cells ml-1). These results suggest that the Götte’s larvae produced by S. ellipticus are obligately feeding. Our observations of development to metamorphosis also confirmed that 4-lobed Götte’s larvae do not transform into 8-lobed Muller’s larvae as development progressed. Instead we observed that metamorphosis in this species proceeds by the gradual resorption of larval lobes prior to the construction of the juvenile pharynx as well as multiplication of presumptive eye spots. The simple culturing methods described here may be useful in expanding our understanding of the larval biology of polyclad flatworms more generally.
