The Antarctic nemertean Parborlasia corrugatus: an example of an extreme oxyconformer

Abstract.

The Antarctic nemertean worm, Parborlasia corrugatus, exhibits gigantism, reaching at least 100 g, yet lacks any specialised respiratory organs. The diffusion of oxygen into this worm occurs cutaneously. We examined the metabolic rate of P. corrugatus at –1°C in response to decreasing ambient PO₂. As the PO₂ of the water decreased, so did the metabolic rate of P. corrugatus, indicating that this nemertean worm is an extreme example of an oxyconformer. When the water PO₂ decreased below about 120 mmHg, the normally short, round worms became elongated and extremely flattened. This behavioural mechanism would allow for an increase in surface area of the skin, thereby facilitating the diffusion of oxygen.