The inverted, motionless sinking behavior of two deep pelagic decapod species.

The head-down, motionless sinking behavior, frequently displayed by the midwater decapod Hymenopenaeus doris in the Gulf of California, Mexico (a-d) and Petalidium suspiriosum in the Monterey Canyon, California (e), may confer visual similarity to molted shrimp exoskeletons (f). Oxygen concentration during respiration experiments of H. doris (g) declined irregularly because we relied on animal movements to mix water. In (g), blue points represent the beginning and end of periods when water was well-mixed by the animal; the slope of linear regressions (black lines) fit to these points calculated routine metabolic rates.