Feeding biology of the mesopelagic gammaridean amphipodParandania boecki(Stebbing, 1888) (Crustacea: Amphipoda: Stegocephalidae) from the Atlantic Ocean

The mouthparts of the mesopelagic stegocephalid amphipod Parandania boecki (Stebbing, 1888) are described in detail and fully illustrated. In a staged encounter with the medusa Atolta parua, P. boecki fed, gripping the edge of the medusa's bell with its thoracopods and held its first antennae aloft, bringing callynophores to face anteriorly. The amphipod also seemed to accept a dead fish as possible food. A porphyrin isolated from the stomach contents of P. boecki was identical to protoporphyrin from Atolla parva. The stomach contents of the amphipod consisted mostly of large pieces of soft tissue (some darkly pigmented) from which nematocysts consistent with those found in A. parva were identified. In addition, crustacean and chaetognath fragments (but no sand grains) were also found. Fe-rich crystals in the ventral gut caeca of P. boecki are identical with others in Stegocephaloides christianiensis shown elsewhere by the authors to be made of ferritin. The concentration of Fe, Cu, Zn and Cd was assessed in P. boecki and a range of medusae. Atolla parva had a higher Fe concentration than the other medusae. If A. parva is the principal prey item of P. boecki, this may account for the amphipods' possessing crystals. We presume the crystals are excreted ultimately and thus that Fe accumulation is limited. The high Cd levels in P. boecki are similar to those in mesopelagic decapod Crustacea. The morphological adaptations of the mouthparts of P. boecki bear striking resemblance to those described as characteristic of certain carrion-feeding lysianassids.