Coeloconic sensilla on the antenna of Locusta migratoria were investigated electrophysiologically, labeled and then examined under the scanning or transmission electron microscope. They can be categorized into two main morphological types: 1) sensilla with wall pores and two concentric cuticular walls (wp-dw sensilla), and 2) sensilla lacking wall pores (np-sensilla). Hygroreceptors were observed only in np-sensilla. Olfactory receptors were observed in wp-dw sensilla, but not in np-sensilla. Cold-sensitive units were fund in both types. Wp-dw sensilla with a cold-sensitive unit also manifest a fatty acid olfactory receptor. This cold-sensitive unit appears to be less sensitive to drops in temperature than the cold receptor combined with hygroreceptors in np-sensilla. Recordings from both types revealed up to three or sometimes four units that could be distinguished on the basis of impulse amplitude. The number of np-sensilla on each antennal segment ranges from 0 to 6. These sensilla are pegs 4--5 micrometer long with a terminal swelling. The dendritic outer segments of two sensory cells fit tightly into these pegs. The dendrite of the third sensory cell ends at its base. All three are up to 1 micrometer thick, unbranched, and densely filled with microtubules. The cuticular wall and socket of the peg are characterized by (1) an electron-dense inner layer surrounding the dendrites and continuous with electron dense clusters at the base of the peg, and (2) clefts in the cuticle at the insertion of the peg. The present observations favor the hypothesis that insect sensilla combining the triad of moist air, dry air and cold receptors generally lack pores. Specifically, though still alternative roles in stimulus transduction can be suggested for substructures demonstrated in the present and previous electron microscopic investigations.
Although the lobate ctenophore Mnemiopsis leidyi is known to be an important copepod predator, the mechanistic basis for its predatory success is not well understood. We directly observed and recorded predation by free-swimming M. leidyi ctenophores on Acartia tonsa and Oithona colcarva copepods (n = 349 encounters, 25 different ctenophores) in the laboratory using videographic methods. Overall capture success was relatively high (74 % ) following copepod contact with M. leidyi. However, average retention of copepods initiaLly contacting the interior surfaces of the oral lobes (the major capture sites) was considerably lower (34 %). Average retention was low because copepods most frequently collided head-first with the oral lobes and bounced away without being captured. Escape success for copepods declined rapidly during ensuing contacts, and most captures (57 "0) involved multiple contacts within an encounter. Our most novel finding was that almost half (49 %) of the encounters involved alterations of oral lobe positions which preceded, or anticipated, actual contact with a copepod. Anticipatory responses were cued to fluid disturbances created by swimming copepods. Anticipation of prey contact allowed ctenophores to shift oral lobe positions and reduce copepod escape avenues, thereby increasing the number of contacts per encounter and significantly increasing capture efficiency.
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