Biserova N.M.1, Korneva J.B.2 2007. [The nervous system ontogeny in cestodes and amphilinids] // Invertebrate Zoology. Vol.3 (for 2006). No.2: 157–184 [in Russian, with English summary].
1 Department of Invertebrate Zoology, Faculty of Biology, Moscow State University, Leninskie Gory, Moscow 119992, Russia. E-mail: firstname.lastname@example.org
2 Institute for Biology of Inland Waters RAS, Borok, Nekouz, Yaroslavl distr. 152742, Russia. E-mail: email@example.com
KEY WORDS: Cestoda, Amphilinida, nervous system, ontogeny, ultrastructure, neurons differentiation, synapse, excretory system, immunocytochemistry.
ABSTRACT: The nervous system (NS) development in all stages of Triaenophorus nodulosus (Pallas, 1781) (Cestoda: Pseudophyllidea), and also juvenile and adult Amphilina foliacea Rud., 1819 (Amphilinida) were studied. The first experimental data concerning the relationship between larval and adult nervous systems in Cestoda have been obtained. Significant differences in the ontogeny of the CNS in amphilinids and cestodes have been observed. We have shown that the oncosphere stage of Cestodes lacked an integrated nervous system because a neuropile and synapses between neurons were absent. Paired neurons (2–4) form contact only with myofibrills of the larval hooks and the body-wall muscle cells. The main processes of development, differentiation and integration in the CNS take place during the first parasitic procercoid stage when the cerebral ganglion, median commissure and main cords are usually formed. The pioneer neurons transit from oncosphere and indicate a way for developing nerves. Undifferentiated cells and developing neurites gather (congregate) around growth axons of the pioneer neurons. Cytodifferentiation of the uni- and bipolar neurons differs from that of the multipolar neurons. The PNS is formed at the next plerocercoid stage, in which also the CNS and sensory organs expand. The nervous system never stops growing in adult cestodes. Growth and formation of main cords and compartments innervating the reproductive organs occur from the stem cells from the neck region.
According to the data by Rohde (1994) and Xylander (2000), lycophora larva of amphilinides has well developed neuropile and many different sensory structures. We showed that young worm has two symmetrical cerebral ganglia of equal size and the connecting median commissure running between the frontal organ and uterus. Adult CNS has an asymmetrical position of the cerebral ganglion, many ganglionar knots in MCs and several well-developed caudal ganglia. In contrast to adult cestodes, the nervous system of adult amphilinids lacks undifferentiated nerve cells. The CNS of amphilinids is more concentrated and has metamerism features. The amphilinids’ CNS has several types of glial cells which produce myeline-like envelopes of the cerebral ganglia and main cords.
In contrast to amphilinds, the cells of the excretory system in adult T. nodulosus can exert glial function and form unique envelopes of the cerebral ganglia and main cords in early stages of ontogeny. We have shown that in the procercoid stage, CNS develops ahead of the development of the excretory system.