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
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ABSTRACT The mesopelagic shrimp Notostomus robustus has been observed from a submersible feeding on the medusa Atolla wyvillei in the northwest Atlantic. Shipboard observations of behavior of the same individuals confirmed this predator/prey relationship, as did an examination of the stomach contents of the shrimp, which included presumed nematocyst capsules and muscle tissue from the bell of the medusa. Electron microscopical examination of shrimp gut contents provided evidence for the ingestion of pelagic clay particles (elemental composition assessed using X-ray probe techniques) also, probably as an indirect result of ingestion by, or adsorption on, the prey. The functional morphology of the feeding appendages of the shrimp was inferred from light microscopical examination of the intact mouthpart bundle and of dissected appendages. The mandible of N. robustus has a small, weakly ridged molar and strongly formed slicing incisor compatible with consumption of soft food items. The mouthpart bundle is accommodated within the confines of the proximally concave proximal article of maxilliped 3, i.e., in such a way as to avoid loss of food fragments in midwater.