SCANNING ELECTRON MICROSCOPIC (SEM) STUDY OF CONGLUTINATES AND CONGLUTINATE-TYPE OBJECTS

Glochidium within pseudo-conglutinate of                      Conglutinate matrix with most of the glochidia
Strophitus undulatus.                                                       released of Obliquaria reflexa.

Nearly all North American freshwater mussels liberate glochidia in specialized packets. These packets are given the broadly-encompassing name 'conglutinates.' Optical and scanning electron microscopy has revealed a surprising complexity in these structures, as well as important phylogenetic information. Anodontines release glochidia in mucous structures lacking any layers. These structures may be amorphous, as in most anodontines, or form discrete structures, as in Strophitus. Amblemines release glochidia contained in their original egg membranes. A significant portion of these conglutinates may be composed of unfertilized eggs. Three morphological groups are apparent within the amblemines. Fusconaia conglutinates are loosely held together by the adhesive properties of the egg membranes, which have no tendency to fuse with each other. In Pleurobema and Elliptio the egg membranes are fused to form a more solid conglutinate. In Quadrula the glochidia are embedded in a mucous matrix. Obliquaria and Dromus conglutinates appear to be derived from the fused membrane condition of Pleurobema/Elliptio but have thicker, almost elastic walls. Other lampsilines (Lampsilis, Ligumia, Potamilus) may form very loose conglutinates composed of glochidia with only vestiges of the egg membranes holding them together. Ptychobranchus produces the most complex conglutinates.

Anodontine 'conglutinates' are morphologically very different from other unionid conglutinate structures, suggesting a distant relationship with other mussel groups. Based on conglutinate morphology, the Mesogenae are extensions of the amblemines and are not related to other lampsilines. The Ptychogenae conglutinates are not similar to any other conglutinate type. Whereas conglutinates of Fusconaia, Pleurobema, and Elliptio are morphologically similar, Quadrula appears distinct.

The pilot study was funded by the Fish Creek Trust Fund. In 2001, the Ohio River Mussel Mitigation Trust funded a greatly expanded study that will examine up to 50 taxa. Stay tuned.