Microscopy and Microanalysis

Taxonomically Important Features on the Surface of Floatoblasts in Plumatella (Bryozoa)

Kevin T.  Reynolds  a1
a1 Department of Biological Sciences, Wright State University, 3640 Colonel Glenn Highway, Dayton, OH 45435


Abstract: At the species level, bryozoans (class Phylactolaemata) in the family Plumatellidae are difficult to organize taxonomically. Of principal concern is the absence of consistent distinguishing features due mainly to plasticity of the group, a common problem with soft-bodied invertebrates. Yet, within the last three decades, analysis of distinctive chitinous statoblasts—using scanning electron microscopy—has resolved certain taxonomic questions. I examined statoblasts from 30 similar collections, the majority from the midwestern United States, and identified four distinct subgroups. Also, nine new statoblast surface features were identified: fold, polar grooves, bead, cave, demarcation, parasutural zone, ridge, sutural band, and sutural knob. The surface features of floating statoblasts (floatoblasts) provide useful data for species identification. Most consistently useful in plumatellids is a suture which varies from one species to the next. Mound-like tubercles and net-like ridges are next in the extent of variability. Finally, folds and polar grooves are present but vary even within floatoblasts from the same colony. Analysis of the suture in PLUMATELLA FUNGOSA, over a 5-day germination period, reveals all features at the site remain intact regardless of the initial age of the floatoblast. Only the suture line itself splits lengthwise to permit emergence of the new animal.