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.
A comparison of surface features on submerged and non-submerged bone using scanning electron microscopy
