THE MESOPELAGIC SHRIMP NOTOSTOMUS-ROBUSTUS SMITH (DECAPODA, OPLOPHORIDAE) OBSERVED IN-SITU FEEDING ON THE MEDUSAN ATOLLA-WYVILLEI HAECKEL IN THE NORTHWEST ATLANTIC, WITH NOTES ON GUT CONTENTS AND MOUTHPART MORPHOLOGY

The mesopelagic shrimp Notostomus robustus has been observed from a su bmersible feeding on the medusa Atolla wyvillei in the northwest Atlan tic. Shipboard observations of behavior of the same individuals confir med this predator/prey relationship, as did an examination of the stom ach contents of the shrimp, which included presumed nematocyst capsule s and muscle tissue from the bell of the medusa. Electron microscopica l examination of shrimp gut contents provided evidence for the ingesti on of pelagic clay particles (elemental composition assessed using X-r ay probe techniques) also, probably as an indirect result of ingestion by, or adsorption on, the prey. The functional morphology of the feed ing appendages of the shrimp was inferred from light microscopical exa mination of the intact mouthpart bundle and of dissected appendages. T he mandible of N. robustus has a small, weakly ridged molar and strong ly formed slicing incisor compatible with consumption of soft food ite ms. The mouthpart bundle is accommodated within the confines of the pr oximally concave proximal article of maxilliped 3, i.e., in such a way as to avoid loss of food fragments in midwater.