Biserova N.M., Gordeev I.I. 2010. [Fine structure of nervous system in plerocercoid Ligula intestinalis (Cestoda: Diphyllobothriidea)] // Invertebrate Zoology. Vol.7. No.2: 133–154 [in Russian, with English summary].
Department of Invertebrate Zoology, Faculty of Biology, Lomonosov Moscow State University, Moscow 119991, Russia; e-mail: email@example.com
KEY WORDS: platyhelmintes, tapeworms, nervous system, ultrastructure, symmetry, polarity, neuron, synapse, Cestoda, Diphyllobothriidea, Ligula intestinalis.
ABSTRACT: The fine structure of the nervous system in plerocercoid Ligula intestinalis (Diphyllobothriidae) has been studied. The ultrastructure of the cerebral ganglion, the main nerve cords and peripheral nervous system has been described. The cerebral ganglion has complicated microanatomy. It consists of symmetric pair frontal and lateral lobes connected by the massive median commissure, and ventral azygos lobe, located in the center and on the ventral surface of the commissure. Two crossed ventral nerves are originated from the unpaired median (ventral) lobe. It was found, that the neurons in the lateral lobes and the commissure have asymmetrical position (localization neurons in the lateral lobes and the commissure has dorso-ventral polarity): large neurons (20–40 µm) are concentrated on the dorsal surface of the cerebral ganglion. We found four types of neurons with different fine structure and size, peripheral neurosecretory cells and undifferentiated cells. Three types of synaptic contacts have revealed in neuropiles. Giant axon occurred as part of the main cord. On the surface membrane of the giant axon are numerous incoming synapses. The peripheral nervous system consists of numerous compact bunches of nerve processes taking place along the longitudinal and dorso-ventral muscle fibers. Also three types of sensory organs were found in the tegument: one type a ciliate and two types unciliate receptors. Comparative analysis of nervous system organization in representatives of the two orders Diphyllobothriidea and Bothriocephalidea showed that the cerebral ganglion L. intestinalis possesses bilateral symmetry, characterized by the presence of the ventral lobe, ventral nerves and the dorso-ventral polarity in the arrangement of neurons and exiting nerves. On the contrary, the cerebral ganglion of Triaenophorus nodulosus (Bothriocephalidea) has a double-beam symmetry: it has symmetrical lobes in ganglion with symmetrical dorsal and ventral nerves, lack of lobe in the median commissure, and send symmetrical dorso-ventral rootlets in the bothria. Our data confirm the belonging of the studied species to different groups and support the idea of separation Pseudophyllidea sensu lato into two new orders Diphyllobothriidea and Bothriocephallidea.