THE FEEDING MECHANISMS AND PREFERRED FOODS OF THREE SPECIES OF PYCNOGONIDA By WILLIAM G. FRY CONTENTS Page SYNOPSIS ........... 197 INTRODUCTION .......... 197 THE FEEDING PREFERENCES OF Austrodecus glaciale AND Rhynchothorax australis ........... 199 Material ........... 199 Maintenance of the organisms ....... 200 Observations . . . . . . . . . .201 Data 201 THE FOOD PREFERENCES OF Pycnogonum stearnsi .... 203 THE MORPHOLOGY OF THE PROBOSCIS IN THE THREE SPECIES . . 203 Methods ........... 203 The extrinsic musculature of the proboscis ..... 204 Taxonomic significance of the disposition of the extrinsic muscles . 209 Previous interpretations of the internal anatomy of the proboscis . 210 The alimentary canal . . . . . . . . . 210 The outer wall of the proboscis and the lips . . . . . 212 The intrinsic musculature of the proboscis . . . . . 213 The nervous system of the proboscis . . . . . . 215 Methods of functioning of the proboscis . . . . . . 216 MORPHOLOGICAL ADAPTATIONS TO PREFERRED FOOD MATERIALS . 217 ACKNOWLEDGEMENTS ......... 222 REFERENCES ........... 222 KEY TO LETTERING IN TEXT-FIGURES AND PLATES .... 223 SYNOPSIS Laboratory experiments demonstrate that Austrodecus glaciale and Rhynchothorax australis, inhabiting the same Antarctic benthic environment, have highly specific and different food preferences. The structures of the proboscides and cephalic somites of the two species are adapted to these food preferences. A . glaciale is the first pycnogonid shown to feed on Polyzoa, while Rh. australis is adapted to feed on hydroid polyps. Pycnogonum stearnsi, from the north-eastern Pacific littoral, which feeds on Actinian tissue, is morphologically very similar to Rh. australis. The disposition of proboscis nerves and muscles in the three species is quite different from anything hitherto described in the Pycnogonida. In previous descriptions basal circular muscles have been interpreted as nerve rings. This prevented, up to now, the proposal of a mechanically reasonable interpretation of the functioning of the proboscis. INTRODUCTION LARGE areas of the sea bottom in McMurdo Sound (Ross Sea, Antarctica) are covered with a dense mat of sponge spicules. Within and on this mat occur large numbers
BioStor
