Convergence upon similar morphological traits is common among predators feeding on similar prey in similar environments. Aboral placement of tentacles during swimming appears to be such a trait and has evolved in parallel among several medusan lineages. Here we examine this trait in 1 scyphomedusa and 2 hydromedusae representing different lineages within the Medusozoa with the goal of evaluating whether aborally directed tentacles function similarly among these varied medusae. We analyzed flow generation, swimming kinematics and swimming behavior of Craspedacusta sowerbyi (Hydrozoa, Limnomedusa), Nausithoë punctata (Scyphozoa, Coronata) and Solmissus albescens (Hydrozoa, Narcomedusa), and the prey capture mechanics of N. puncatata. The 3 species swam similarly and generated similar wake structures in comparison to each other and to oblate medusae with trailing tentacles. Foraging behavior, as measured by the percent of time spent swimming, was similar for medusae possessing both leading and trailing tentacle placement. These findings indicate that medusae possessing either type of tentacle placement swim and forage similarly but that medusae with leading tentacles capture prey 'upstream' while medusae with trailing tentacles capture prey 'downstream' of vortices generated at the bell margin during swimming. These differences in tentacle placement relative to flow around the medusae may have important consequences for prey capture and trophic interactions that lead to different prey-selection patterns.

The widespread occurrence and frequent abundance of small hydromedusae suggests that they may play an important role in planktonic communities. However, rather than exhibiting dominant impacts on any specific planktonic group, field studies have demonstrated diverse dietary niches and only modest trophic impacts by small hydromedusae. To understand the functional bases for these patterns, we exposed 2 hydromedusae (Cladonema californicum and Leuckartiara sp.) to a variety of prey types (dinoflagellates, rotifers, barnacle nauplii, copepods and the hydromedusa Obelia sp.) while video-recording predation sequences (encounter, capture, ingestion). Both C. californicum and Leuckartiara sp. ambush prey and possess penetrating nematocysts (stenoteles and euryteles, respectively). Although similar prey selection patterns might be expected based on encounter models or nematocyst complements, the 2 species exhibited some markedly different ingestion patterns. For example, C. californicum positively selected copepod prey and negatively selected hydromedusae, whereas Leuckartiara sp. exhibited the opposite pattern. Quantification of predation sequences demonstrated that hydromedusan dietary variations resulted from speciesspecific differences in prey capture efficiencies as well as efficiencies in post-capture transfer to the gut. Species-specific prey selection patterns and limited ingestion capacities may explain the diverse prey selection patterns and limited trophic significance observed in field studies of ambush-foraging hydromedusae.