THE FORMATION AND TAXONOMIC STATUS OF THE MICROBASIC Q-MASTIGOPHORE NEMATOCYST OF SEA ANEMONES

¹ Department of Biological Science, Florida State University, Tallahassee, Florida 32306

Detachable darts, supposedly diagnostic of the microbasic q-mastigophore nematocyst, are formed by the adhesion of shaft spines of two different nematocysts: the microbasic amastigophore and microbasic p-mastigophore. Based on the morphology of their shaft spines, each of the nematocysts can be subdivided into two additional types, A and B. Only the type B nematocysts are capable of forming darts.

Dart formation by tentacle nematocysts was rare, but was relatively common among type B acontial or column vesicle nematocysts. Experiments showed that darts were formed by acontial nematocysts, for example, about 27 times more frequently than by tentacle nematocysts, both intra- and interspecifically. However, only a relatively small percentage of type B nematocysts appeared capable of forming darts in the material examined.

Darts were propelled out of the capsule with sufficient force to penetrate crustacean exoskeleton. Because of this and evidence from the experimental studies, it is suggested that dart formation may play a role in the defense of some anemones against benthic predators. Although possibly having functional significance for those anemones possessing the appropriate nematocyst, dart formation caused by the fusion of shaft spines among only a certain percentage of the nematocyst population indicates that the microbasic q-mastigophore is not a valid nematocyst type.