ABSTRACT: Our study aimed at determining which types of sensors are associated with setae on the cephalic appendages of marine calanoid copepods that create feeding currents. Such sensors enable copepods to rapidly identify potential food particles in the ambient water current, probably through chemical or hydrodynamic signals from the particles. We examined 4 copepod species, Centropages velificatus, Eucalanus pileatus, Paracalanus aculeatus and Temora stylifera, by scanning (SEM) and transmission (TEM) electron microscopy. Copepodids and adult females of all 4 species bear apical pores on the setae of their maxillipeds and second antennae, indicating potential chemoperceptive capabilities. TEM revealed putative chemo- and mechanosensors on the mandibular palp of C. velificatus and the second antennae of T. stylifera, supporting an earlier, similar report of sensors on the maxilliped of T. stylifera. As the setae of these 3 appendages are in almost continuous motion, at frequencies between 25 Hz (female E. pileatus) and 80 Hz (female P. aculeatus), food particles beyond the reach of the setae are believed to be recognised chemically by the apical pores of the individual setae. The observed mechanosensors are presumably used when handling larger food particles, as already described for T. stylifera during capture and alignment of elongated cells prior to ingestion.

KEY WORDS: Ultrastructure · Setae · Cephalic appendage · Marine planktonic copepods

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Published in MEPS Vol. 203 (2000) on September 18
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 2000