In situ foraging and feeding behavior of narcomedusae (Cnidaria: Hydrozoa)

Narcomedusae are a small and mostly oceanic group of hydromedusae whose tentaclemorphology and comportment sets them off behaviourally and perhaps ecologically frommost other medusae. Their tentacles are relatively few in number (2-40), stiff, and noncontractile,with points of insertion located well above the bell margin. Eleven speciesrepresenting eight narcomedusan genera (Aegina, Aeginura,an undescribed aeginid, Cunina,Pegantha, Solmaris, Solmissus, and Solmundella) were observed and collected in situ in theNW Atlantic, Arctic and Antarctic, using scuba and manned submersibles. In life, thetentacles of narcomedusae are nearly always held upwards over the bell or projectedlaterally. The major prey were other gelatinous zooplankton, especially salps and doliolids.In the laboratory, these relatively large prey were caught on the tentacles which bendinward and coil at the tips to bring food to the mouth. By extending the tentaclesperpendicular to the swimming path, these medusae achieve a relatively large encounterarea, thus increasing the probability of contact with prey, for the amount of protein invested in tentacles.