Cnidarians are the largest phylum of generally toxic animals, yet their toxins and venoms have not received as much scientific attention as those of many terrestrial (snakes, scorpions, spiders, etc.) and even some marine animals (i.e. cone snails). Approximately 13,000 living cnidarian species have been described by systematists. A major rationale for their study in the past, besides scientific curiousity, was to better treat victims of their envenomation. While that goal remains a high priority, it is now appreciated that the toxins of these mostly marine animals can be very useful molecular probes for the analysis of ion channels involved in electrical signaling, immune responses and other signal transduction processes of biomedical interest. For instance, anaphylaxis was discovered by Richet (1905) during experiments with sea anemone and hydrozoan tentacular extracts. Similarly, it has recently been shown that a toxin from another sea anemone is able to potently inhibit T-lymphocyte proliferation in models of certain autoimmune diseases. Thus, these natural substances continue to be of relevance for understanding and treating human diseases. In addition to introducing phylum Cnidaria (Coelenterata), we provide a short history of early (until about 1990) research on cnidarian toxins and venoms, to provide a perspective for appreciating the scientific advances of the past two decades that are summarized in the ensuing 19 papers in this special Toxicon issue.

We analyzed the relationship between prey capture and nematocyst distribution in the tentacles of the ambush predators, Aglantha digitale and Proboscidactyla flavicirrata, and the filter feeders, Clytia gregaria and Mitrocoma cellularia. we used video observations to compare capture locations of Artemia salina nauplii relative to the bell margin of each species. Tentacle pictures were analyzed to determine if nematocyst abundance changes along their length. By analyzing behavior and morphology simultaneously, we found that the ambush predators A. digitale and P. flavicirrata plus Sarsia tubulosa have higher nematocyst density at the tentacle tips and tend to capture more prey toward the tips. In contrast, the filter-feeders Aequorea victoria, C. gregaria and M. cellularia capture most of the prey close to the body, where they also show a slight increase in nematocyst densities.

Recent molecular evidence suggests staurozoans are medusozoans that diverged from Medusozoa before the medusa stage emerged. Morphological studies are needed to determine whether this framework can provide insight into medusa evolution. I studied the neuromuscular morphology of two staurozoans, Haliclystus ‘sanjuanensis’ and Manania handi using FMRFamide and α-tubulin antibodies to label neurons, and phalloidin to label muscles. Results indicate that similar to polyps, staurozoans possess one regionally differentiated FMRFamide and α-tubulin immunoreactive (IR) nerve net, and smooth muscles only. Comparisons with other cnidarians indicate that ancestral medusozoans had a marginal circular muscle and muscular manubrium, but lacked the parallel conducting nerve nets, striated muscle, and pacemaker required to coordinate medusa swimming. A possibly light-sensitive concentration of neurons at the base of the primary tentacles suggests that staurozoan primary tentacles are homologous to medusozoan rhopalia. The unique neuromusculature of nematocyst clusters suggests a defensive or predatory function for these staurozoan synapomorphies. / Graduate / 0287 / 0317