Meeting Abstract
Rotifers are some of the most common aquatic invertebrates in freshwater systems. Most rotifers are planktonic and easily recognized by their ciliated corona and hardened jaws called trophi, but many species in the superorder Gnesiotrocha are sessile on submerged vegetation and defined in part by their abilities to produce tubular sheaths around their bodies. These tubes are hypothesized to have defensive functions and are present in a variety of morphologies as gelatinous sheaths, hardened pipe-like secretions, and tubes of pseudofecal pellets. The morphology of the tubes appears to be independent of phylogeny as some closely related species produce entirely different tube types, while distantly related species may produce morphologically identical tubes. In an effort to gain a better understanding of tube diversity, we explored the ultrastructure of various tubes by scanning and transmission electron microscopy. We find that most gelatinous tubes (e.g., species of the distantly related genera Conochilus and Stephanoceros) share a similar ultrastructure that consists of a network of fine electron-dense secretions that probably function to hold an aqueous medium in place. These matrices appear to be derived from the pedal glands of the foot. Other species such as those of some Floscularia produce pseudofecal pellets and layer them atop a thin gelatinous membrane that is similar in ultrastructure to the gelatinous tubes. Alternatively, the hardened pipe-like matrices present in species of Limnias appear to derived from trunk glands, and consist of a homogeneous opaque material that is devoid of any gelationus matrix. The widespread distribution of gelatinous matrices produced by pedal glands points to their early evolution and one that may define the sessile Gnesiotrocha, while the hardened matrices of Limnias appears to be an independently derived secretion.
