The Role of Scanning Electron Microscopy in Taxonomic Studies of Freshwater Bryozoans (Ectoprocta: Phylactolaemata)

Extract

Bryozoans are among the most common multicellular animals that attach to submerged surfaces in fresh waters. Zooids of the colony capture and digest suspended food particles; they also produce distinctive asexual buds called statoblasts. Measuring 0.35 to nearly 1 mm in diameter, statoblasts have a chitinous exterior and are the only truly hard parts of the bryozoan colony. Like the mastax of rotifers or mouthparts of midge larvae, statoblasts show a variety of taxonomically significant features. Scanning electron microscopy reveals clear patterns in statoblast surface topography that suggest many more species than the 60 or so normally recognized.

Statoblast surface features were first used to distinguish species of the genus Fredericella. The European F. sultana, with a smooth statoblast surface, had been assumed to occur worldwide. SEM micrographs showed the statoblast surface of New World Fredericella to be finely pitted, identical to that of F. indica in India (Figure 1). Another Fredericella species, not yet named, is distinguished only by its highly rugose statoblast surface (Figure 2). Such features are retained through generations of laboratory rearing under various controlled conditions.