A new stylochid flatworm (Platyhelminthes, Polycladida) from Victoria, Australia and observations on its biology

Abstract

There are only four polyclad flatworms currently known from temperate waters of Victoria, Australia, although these turbellarians are common inhabitants of rocky shores. A new stylochid flatworm, Stylochus pygmaeus sp. nov. (Platyhelminthes, Polycladida) or oyster leech is described here from Port Philip Bay, Victoria. This flatworm was observed feeding on three species of barnacles by extending its pharynx over its prey and extruding copious amounts of mucus. Worms also preferred to prey on larger‐sized barnacles regardless of the species. Further observations indicated that these worms deposited eggs at night inside empty barnacle shells. Each eggmass was brooded for several days with the worms only moving off to feed. Each egg capsule contained multiple embryos and after 5 or 6 days, positively photo‐tactic, four‐lobed Götte's larvae emerged. Larvae metamorphosed to juvenile flatworms 1–2 weeks post‐hatching but failed to settle and survive.

Keywords:

• Barnacles
• Götte's larvae
• oyster leech
• new species
• Platyhelminthes
• Polycladida
• predators
• Stylochidae
• Stylochus pygmaeus

Acknowledgements

We would like to thank Mr Bruce Abaloz, University of Melbourne for sectioning egg capsules and Mr David Paul, University of Melbourne for photographing live animals. Special thanks to Lester Cannon for reviewing this manuscript; Ray Johnson and the staff of the Northern Rivers Pathology, Lismore Base Hospital for the histological serial sections; the Auckland Museum, New Zealand; the School of Environmental Science and Management, Southern Cross University; and Prof. D. Macmillan, Zoology Department, University of Melbourne. Funding was provided to L.J.N. by a grant from the Australian Biological Resource Study, Canberra.