Ultrastructure of presumed sensory receptors in the scolex of adult Proteocephalus exiguus (Cestoda, Proteocephalidea)

Ultrastructure of the early gravid uterus of Corallobothrium fimbriatum (Cestoda: Proteocephalidea)

The ultrastructure of the uterine epithelium and underlying extracellular matrices has been studied in several cyclophyllideans, but relatively little has been published on uterine fine structure in other cestode orders. To develop comparative data, we initiated a study focusing on a common and widespread genus of the order Proteocephalidea. Adult specimens of Corallobothrium fimbriatum were removed from the small intestine of brown bullhead catfish, Ameiurus nebulosus, from the St. Lawrence River in North America. Early gravid proglottids were examined by light microscopy as whole mounts or diced in buffered glutaraldehyde, processed by standard techniques and examined by as stained sections by light microscopy and by transmission electron microscopy. Voucher specimens were deposited in the Museum of Comparative Zoology at Harvard University. The uterus consisted of an epithelial wall supported basally by an extracellular matrix and parenchyma cells, which together formed epitheliomesenchymal villi at many points. The uterine epithelium consisted of a single thin syncytial layer, folded distally into long epithelial villi that protruded into the lumen at some points. The epithelium's numerous nuclei were very close to the lumen, but bulged along with the perinuclear cytoplasm proximally into the surrounding medullary parenchyma. Each nucleus contained small amounts of evenly dispersed heterochromatin and euchromatin, with a central nucleolus. Numerous mitochondria occurred in the cytoplasm, which was densely filled with free ribosomes but contained scant endomembrane components and showed little evidence of secretory activity. The uterine cells possessed few of the apical microvilli that are typical of some cyclophyllidean species, but the apical plasma membrane and cortical cytoplasm were extensively developed into long microlamellae similar to other species. The basic syncytial nature of the epithelium is similar to that of other cestodes studied previously, but the specific combination of features is unlike any previously described. Based on this one proteocephalidean species, we discerned no pattern that would distinguish between Proteocephalidea and Cyclophyllidea based on uterine structure.

Ultrastructure of the early rostellum of Silurotaenia siluri (Batsch, 1786) (Cestoda: Proteocephalidae)

The neodermis of the whole early rostellum of Silurotaenia siluri (Batsch, 1786) bears filamentous microtriches. At the base, there are five to six irregular rows of hooks and spine-like microtriches. The rostellar hooks of S. siluri originate through the enlargement of microtriches. Electron-dense hook substance is deposited along the edges of the microthrix to form the hook blade and basal plate. The blade does not become hollow as in the cyclophyllidean cestodes. The basal plate of the hook, corresponding to the handle and the guard of Cyclophyllidea, is formed by the deposition of hook substance around the base of the microthrix. Within the centre of the base, only a narrow cleft-like core is occupied by distal cytoplasm. The hook bases are more deeply inserted into the distal cytoplasm, as the bases of the spine-like microtriches are localized on the rostellum below the rows of hooks. No hemidesmosomes, fixing the hook base to the basal lamina, are present. Eccrine gland cells and uniciliate and nonciliate sensory receptors of the primitive rostellum are described.

Neuropeptides in flatworms

The use of well-characterized antibodies raised to neuronal signal substances and their application through immunocytochemistry and confocal scanning laser microscopy has revolutionized studies of the flatworm nervous system (NS). Data about flatworm neuropeptides and the spatial relationship between neuropeptides and other neuronal signal substances and muscle fibers are presented. Neuropeptides form a large part of the flatworm NS. Neuropeptides are especially important as myoexcitatory transmitters or modulators, controlling the musculature of the attachment organs, the stomatogastric and the reproductive systems.