Feeding ecology of detritivorous and carnivorous pelagic copepods

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1. Eleven genera belonging to the detritivorous calanoid families Diaixidae, Phaennidae, Scolecitrichidae and Tharybidae have special sensory setae on the maxillae and maxillipeds. Worm-like and brush-like sensory setae are commonly found in these taxa. In addtition to these two sensory setae some taxa have different ones. These sensory setae are probably chemoreceptors based on the fine structures. Worm-like and brush-like sensory setae are different in the number and configuration of microtubule bands, which may indicate different sensitivity. Gut content analyzes revealed that they fed on detritus such as appendicularian houses and crustacean carcasses and/or exuviae. Cephalophanes spp. with a pair of large reflecting eyes exclusively fed on crustacean fragments, suggesting that these reflecting eyes may play roles in detection of detritus. Nine species of the poecilostomatoid Oncaea from Red Sea frequently fed on appendicularian house. 2. The carnivorous calanoid Heterorhabdus has a hollow mandibular ventralmost tooth with a subterminal pore and a basal opening. The distal region of the tooth is hypodermic needle-like and is strengthened by opal layrs. The posterior surface of the labrum carries a lateral pair of large gland openings, which are located close to, and appear to fit exactly the basal openings of the ventralmost teeth. Venom or anaesthetic is injected from the labral openings into the tubular structure of the mandibular ventralmost tooth, and then released into the prey from its subterminal pore immediately after capture of prey macrozooplankters such as copepodids and polychaetes with the stout maxillae. A cladistic analysis inferred that the most advanced genera, Heterorhabdus, Hemirhabdus and Neorhabdus, carry these specialized structures in the mandible and labrum in the family. Any other carnivorous calanoids have never been reported to employ such a specialized feeding mechanism.