Neuronal gene expression in two generations of the marine parasitic worm, Cryptocotyle lingua.

Trematodes, or flukes, undergo intricate anatomical and behavioral transformations during their life cycle, yet the functional changes in their nervous system remain poorly understood. We investigated the molecular basis of nervous system function in Cryptocotyle lingua, a species of relevance for fisheries. Transcriptomic analysis revealed a streamlined molecular toolkit with the absence of key signaling pathways and ion channels. Notably, we observed the loss of nitric oxide synthase across the Platyhelminthes. Furthermore, we identified upregulated neuronal genes in dispersal larvae, including those involved in aminergic pathways, synaptic vesicle trafficking, TRPA channels, and surprisingly nitric oxide receptors. Using neuronal markers and in situ hybridization, we hypothesized their functional relevance to larval adaptations and host-finding strategies. Additionally, employing a behavior quantification toolkit, we assessed cercaria motility, facilitating further investigations into the behavior and physiology of parasitic flatworms. This study enhances our understanding of trematode neurobiology and provides insights for targeted antiparasitic strategies.

A miniaturized nigrostriatal-like circuit regulating locomotor performance in a protochordate.

To gain insight into the evolution of motor control systems at the origin of vertebrates, we have investigated higher-order motor circuitry in the protochordate Oikopleura dioica. We have identified a highly miniaturized circuit in Oikopleura with a projection from a single pair of dopaminergic neurons to a small set of synaptically coupled GABAergic neurons, which in turn exert a disinhibitory descending projection onto the locomotor central pattern generator. The circuit is reminiscent of the nigrostriatopallidal system in the vertebrate basal ganglia, in which disinhibitory circuits release specific movements under the modulatory control of dopamine. We demonstrate further that dopamine is required to optimize locomotor performance in Oikopleura, mirroring its role in vertebrates. A dopamine-regulated disinhibitory locomotor control circuit reminiscent of the vertebrate nigrostriatopallidal system was thus already present at the origin of ancestral chordates and has been maintained in the face of extreme nervous system miniaturization in the urochordate lineage.

Post-gastrulation transition from whole-body to tissue-specific intercellular calcium signaling in the appendicularian tunicate Oikopleuradioica.

We recently described calcium signaling in the appendicularian tunicate Oikopleura dioica during pre-gastrulation stages, and showed that regularly occurring calcium waves progress throughout the embryo in a characteristic spatiotemporal pattern from an initiation site in muscle lineage blastomeres. Here, we have extended our observations to the period spanning from gastrulation to post-hatching stages. We find that repetitive Ca2+ waves persist throughout this developmental window, albeit with a gradual increase in frequency. The initiation site of the waves shifts from muscle cells at gastrulation and early tailbud stages, to the central nervous system at late tailbud and post-hatching stages, indicating a transition from muscle-driven to neurally driven events as tail movements emerge. At these later stages, both the voltage gated Na+ â€‹channel blocker tetrodotoxin (TTX) and the T-type Ca2+ channel blocker and nAChR antagonist mecamylamine eliminate tail movements. At late post-hatching stages, mecamylamine blocks Ca2+ signals in the muscles but not the central nervous system. Post-gastrulation Ca2+ signals also arise in epithelial cells, first in a haphazard pattern in scattered cells during tailbud stages, evolving after hatching into repetitive rostrocaudal waves with a different frequency than the nervous system-to-muscle waves, and insensitive to mecamylamine. The desynchronization of Ca2+ waves arising in different parts of the body indicates a shift from whole-body to tissue/organ-specific Ca2+ signaling dynamics as organogenesis occurs, with neurally driven Ca2+ signaling dominating at the later stages when behavior emerges.

Basal metabolic rate in free-ranging tropical birds lacks long-term repeatability and is influenced by ambient temperature.

Tropical birds live longer, have smaller clutches and invest more resources into self-maintenance than temperate species. These "slow" life-histories in tropical birds are accompanied by low basal metabolic rate (BMR). It has recently been suggested that the low BMR of tropical species may be related not to their slow "pace of life" or high ambient temperatures (Ta ) in tropical latitudes, but to the stability of environmental conditions in tropics. Since the repeatability of metabolic traits is higher in stable environments, such as laboratory conditions, we predicted that long-term repeatability of BMR in a tropical climate should be higher than in a temperate one. Contrary to our predictions, the repeatability of mass-independent BMR in 64 individuals of free-living tropical birds from Vietnam was low and insignificant after the species affiliation was taken into account. It indicates that BMR cannot be used as an individual long-term characteristic of tropical birds. On the other hand, tropical birds showed consistent differences in their mass-independent BMR at the interspecific level. Using BMR measurements from 1543 individuals of 134 species, we also found that different characteristics of Ta within the week preceding BMR measurements had a significant impact on the mass-independent BMR of tropical birds. The most significant effect was the difference between the absolute maximum and minimum Ta within a single week. Our results indicate that the physiology of tropical birds is more subject to changes than would be expected based on the notion of the stability of climatic conditions in the tropics.

Diversity and host associations of Myrsidea chewing lice (Phthiraptera: Menoponidae) in the tropical rainforest of Malaysian Borneo.

The tropical rainforests of Sundaland are a global biodiversity hotspot increasingly threatened by human activities. While parasitic insects are an important component of the ecosystem, their diversity and parasite-host relations are poorly understood in the tropics. We investigated parasites of passerine birds, the chewing lice of the speciose genus MyrsideaWaterston, 1915 (Phthiraptera: Menoponidae) in a natural rainforest community of Malaysian Borneo. Based on morphology, we registered 10 species of lice from 14 bird species of six different host families. This indicated a high degree of host specificity and that the complexity of the system could be underestimated with the potential for cryptic lineages/species to be present. We tested the species boundaries by combining morphological, genetic and host speciation diversity. The phylogenetic relationships of lice were investigated by analyzing the partial mitochondrial cytochrome oxidase I (COI) and the nuclear elongation factor alpha (EF-1α) genes sequences of the species. This revealed a monophyletic group of Myrsidea lineages from seven hosts of the avian family Pycnonotidae, one host of Timaliidae and one host of Pellorneidae. However, species delimitation methods supported the species boundaries hypothesized by morphological studies and confirmed that four species of Myrsidea are not single host specific. Cophylogenetic analysis by both distance-based test ParaFit and event-based method Jane confirmed overall congruence between the phylogenies of Myrsidea and their hosts. In total we recorded three cospeciation events for 14 host-parasite associations. However only one host-parasite link (M. carmenae and their hosts Terpsiphone affinis and Hypothymis azurea) was significant after the multiple testing correction in ParaFit. Four new species are described: Myrsidea carmenae sp.n. ex Hypothymis azurea and Terpsiphone affinis, Myrsidea franciscae sp.n. ex Rhipidura javanica, Myrsidea ramoni sp.n. ex Copsychus malabaricus stricklandii, and Myrsidea victoriae sp.n. ex. Turdinus sepiarius.

Transcriptional adaptation in Caenorhabditis elegans.

Transcriptional adaptation is a recently described phenomenon by which a mutation in one gene leads to the transcriptional modulation of related genes, termed adapting genes. At the molecular level, it has been proposed that the mutant mRNA, rather than the loss of protein function, activates this response. While several examples of transcriptional adaptation have been reported in zebrafish embryos and in mouse cell lines, it is not known whether this phenomenon is observed across metazoans. Here we report transcriptional adaptation in C. elegans, and find that this process requires factors involved in mutant mRNA decay, as in zebrafish and mouse. We further uncover a requirement for Argonaute proteins and Dicer, factors involved in small RNA maturation and transport into the nucleus. Altogether, these results provide evidence for transcriptional adaptation in C. elegans, a powerful model to further investigate underlying molecular mechanisms.

Five New Species of Guimaraesiella (Phthiraptera: Ischnocera) from Broadbills (Aves: Passeriformes: Calyptomenidae: Eurylaimidae).

Five new species of Guimaraesiella Eichler, 1949 are described and illustrated from hosts in the Eurylaimidae and Calyptomenidae. They are Guimaraesiella corydoni n. sp. from Corydon sumatranus laoensis Meyer de Schauensee, 1929 ; Guimaraesiella latirostris n. sp. from Eurylaimus ochromalus Raffles, 1822 ; Guimaraesiella cyanophoba n. sp. from Cymbirhynchus macrorhynchus malaccensis Salvadori, 1874 and C. m. siamensis Meyer de Schauensee and Ripley, 1940 ; Guimaraesiella altunai n. sp. from Calyptomena viridis caudacuta Swainson, 1838 ; and Guimaraesiella forcipata n. sp. from Eurylaimus steerii steerii Sharpe, 1876 . These represent the first species of Guimaraesiella described from the Calyptomenidae and Eurylaimidae, as well as the first species of this genus described from the Old World suboscines.

Gap junction-dependent coordination of intercellular calcium signalling in the developing appendicularian tunicate Oikopleura dioica.

We characterized spontaneous Ca2+ signals in Oikopleura dioica embryos from pre-fertilization to gastrula stages following injection of GCaMP6 mRNA into unfertilized eggs. The unfertilized egg exhibited regular, transient elevations in intracellular Ca2+ concentration with an average duration of 4-6 s and an average frequency of about 1 every 2.5 min. Fertilization was accompanied by a longer Ca2+ transient that lasted several minutes. Thereafter, regular Ca2+ transients were reinstated that spread within seconds among blastomeres and gradually increased in duration (by about 50%) and decreased in frequency (by about 20%) by gastrulation. Peak amplitudes also exhibited a dynamic, with a transitory drop occurring at about the 4-cell stage and a subsequent rise. Each peak was preceded by about 15 s by a smaller and shorter Ca2+ increase (about 5% of the main peak amplitude, average duration 3 s), which we term the "minipeak". By gastrulation, Ca2+ transients exhibited a stereotyped initiation site on either side of the 32-64-cell embryo, likely in the nascent muscle precursor cells, and spread thereafter symmetrically in a stereotyped spatial pattern that engaged blastomeres giving rise to all the major tissue lineages. The rapid spread of the transients relative to the intertransient interval created a coordinated wave that, on a coarse time scale, could be considered an approximate synchronization. Treatment with the divalent cations Ni2+ or Cd2+ gradually diminished peak amplitudes, had only moderate effects on wave frequency, but markedly disrupted wave synchronization and normal development. The T-type Ca2+ channel blocker mibefradil similarly disrupted normal development, and eliminated the minipeaks, but did not affect wave synchronization. To assess the role of gap junctions in calcium wave spread and coordination, we first characterized the expression of two Oikopleura connexins, Od-CxA and Od-CxB, both of which are expressed during pre-gastrulation and gastrula stages, and then co-injected double-stranded inhibitory RNAs together with CGaMP6 to suppress connexin expression. Connexin mRNA knockdown led to a gradual increase in Ca2+ transient peak width, a decrease of interpeak interval and a marked disruption of wave synchronization. As seen with divalent cations and mibefradil, this desynchronization was accompanied by a disruption of normal development.

Food Sensation Modulates Locomotion by Dopamine and Neuropeptide Signaling in a Distributed Neuronal Network.

Finding food and remaining at a food source are crucial survival strategies. We show how neural circuits and signaling molecules regulate these food-related behaviors in Caenorhabditis elegans. In the absence of food, AVK interneurons release FLP-1 neuropeptides that inhibit motorneurons to regulate body posture and velocity, thereby promoting dispersal. Conversely, AVK photoinhibition promoted dwelling behavior. We identified FLP-1 receptors required for these effects in distinct motoneurons. The DVA interneuron antagonizes signaling from AVK by releasing cholecystokinin-like neuropeptides that potentiate cholinergic neurons, in response to dopaminergic neurons that sense food. Dopamine also acts directly on AVK via an inhibitory dopamine receptor. Both AVK and DVA couple to head motoneurons by electrical and chemical synapses to orchestrate either dispersal or dwelling behavior, thus integrating environmental and proprioceptive signals. Dopaminergic regulation of food-related behavior, via similar neuropeptides, may be conserved in mammals.

Functionally asymmetric motor neurons contribute to coordinating locomotion of Caenorhabditis elegans.

Locomotion circuits developed in simple animals, and circuit motifs further evolved in higher animals. To understand locomotion circuit motifs, they must be characterized in many models. The nematode Caenorhabditis elegans possesses one of the best-studied circuits for undulatory movement. Yet, for 1/6th of the cholinergic motor neurons (MNs), the AS MNs, functional information is unavailable. Ventral nerve cord (VNC) MNs coordinate undulations, in small circuits of complementary neurons innervating opposing muscles. AS MNs differ, as they innervate muscles and other MNs asymmetrically, without complementary partners. We characterized AS MNs by optogenetic, behavioral and imaging analyses. They generate asymmetric muscle activation, enabling navigation, and contribute to coordination of dorso-ventral undulation as well as anterio-posterior bending wave propagation. AS MN activity correlated with forward and backward locomotion, and they functionally connect to premotor interneurons (PINs) for both locomotion regimes. Electrical feedback from AS MNs via gap junctions may affect only backward PINs.

Captive individuals of endangered Philippine raptors maintain native feather mites (Acariformes: Pterolichoidea) species.

Endangered species of hosts are coupled with endangered species of parasites, which share the risk of co-extinction. Conservation efforts sometimes include breeding of rare species in captivity. Data on parasites of captive populations of endangered species is scarce and the ability of small numbers of captive host individuals to support the biodiversity of native parasites is limited. Examination of ectosymbionts of the critically endangered Philippine eagles and the endangered Mindanao Hawk-Eagle kept at the Philippine Eagle Center, Philippines, revealed three feather mite species despite regular treatment with insecticide powder. No other ectosymbiont taxa were detected. Studies in morphology and molecular phylogeny of these feather mites based on mitochondrial and nuclear DNA markers indicate that species found were typical for Accipitridae. Three new pterolichoid feather mite species (Acari: Pterolichoidea) were described from two species of eagles (Accipitriformes: Accipitridae) endemic to the Philippines: Hieracolichus philippinensis sp. n. (Gabuciniidae) and Pseudalloptinus pithecophagae sp. n. (Pterolichidae) from the Great Philippine Eagle Pithecophaga jefferyi Ogilvie-Grant, 1896, and Pseudogabucinia nisaeti sp. n. (Kramerellidae) from the Mindanao Hawk-Eagle Nisaetus pinskeri Gould, 1863. The presence of H. philippinensis on P. jefferyi supports the recent finding that the Great Philippine Eagle belongs to the lineage of serpent eagles (Circaetinae) rather than to the Harpy and other eagles.

Basal metabolic rate in free-living tropical birds: the influence of phylogenetic, behavioral, and ecological factors.

The majority of our knowledge of avian energetics is based on studies of birds from temperate and high latitudes. Using the largest existing sample of wild-caught Old World tropical species, we showed that birds from Southern Vietnam had lower basal metabolic rate (BMR) than temperate species. The strongest dissimilarity between tropical and temperate species was the low scaling exponent in the allometric relation between BMR and body mass in tropical birds (the regression slope was 0.573). The passerine migrants to temperate and high latitudes had higher BMR than tropical sedentary passerines. Body mass alone accounted for 93% of the variation in BMR (body mass ranged from 5 to 252 g). Contrary to some other studies, we did not find evidence besides the above mentioned that phylogeny, taxonomy, behavior, or ecology have a significant influence on BMR variation among tropical birds.

Myrsidea claytoni (Phthiraptera: Menoponidae) from Cymbirhynchus macrorhynchos (Passeriformes: Eurylaimidae): a case of natural host switching.

Thirty-two black-and-red broadbill Cymbirhynchus macrorhynchos were examined for chewing lice in Vietnam. All birds examined were parasitized by Myrsidea claytoni. Mean abundance was 27.3, with intensity range 5-80 lice per bird. This is the first report of a Myrsidea from this host, although the females differ slightly from the original description of M. claytoni from Pycnonotus eutilotus in the shape of metanotum and of tergites I-II. So this is also the first record of 1 species of Myrsidea from 2 very distantly related hosts. Although the original hosts of M. claytoni belong to the family Pycnonotidae, C. macrorhynchos is a member of the family Eurylaimidae, representing the Old World Suboscines, which are considered as a basal lineage among passerines. Therefore, our record represents an interesting case of natural host switching. The high prevalence as well as the intensity of infestation show that M. claytoni is well established on C. macrorhynchos in Vietnam.

The neuromuscular system in continuously swimming cercariae from Belarus. II Echinostomata, Gymnocephala and Amphistomata.

The neuromuscular system in cercariae of Moliniella anceps, Echinostoma revolutum, Cathaemasia hians, Psilochasmus oxyurus, Sphaeridiotrema globulus, Paramphistomum cervi and Diplodiscus subclavatus was studied with immunocytochemical methods and confocal scanning laser microscopy. The patterns of F-actin in the musculature, 5-HT immunoreactive (IR), FMRFamide-IR neuronal elements and α-tubulin-IR sensory receptors were investigated. The general patterns of musculature, 5-HT- and FMRFamide-IR neuronal elements in the 12 species studied here and in paper I are similar to those observed in other cercariae and reflect the morphology of the groups. The musculature of the tail shows variations which are related to the different strategies of host finding. In the Echinostomatoidea and Paramphistomoidea, the striated musculature of the tail is well developed compared to that in the Xiphidiocercariae. Specialized muscle fibres were found in S. globulus, which are able to change the shape of the tail. Nine of the species studied have seven paired 5-HT-IR neurons in the body, and two species have eight. No correlation between the body size and the number of 5-HT-IR neurons was observed. However, the size of the neurons followed the body size. The number of 5-HT-IR neurons in the brain ganglia increased from the primitive to the advanced forms. The number of FMRFamide-IR transverse commissures in the body correlates with the size of the cercariae. Regardless of the differences in the second intermediate host, the distribution of α-tubulin-IR sensory receptors shows a high degree of conformity in all species except in P. cervi, which encysts on plants.

The neuro-muscular system in continuously swimming cercariae from Belarus. I Xiphidiocercariae.

The neuromuscular system (NMS) in cercariae of Neoastiotrema trituri, Plagiorchis elegans, Omphalometra flexuosa, Skrjabinoeces similis and Prosthogonimus ovatus was studied with immunocytochemical methods and confocal scanning laser microscopy. The patterns of F-actin in the musculature, 5-HT immunoreactive (IR), FMRFamide-IR neuronal elements and α-tubulin-IR sensory receptors were investigated, and they were found to be rather similar in all the cercariae studied. Four species have seven paired 5-HT-IR neurons in the body, and P. elegans has eight. N. trituri has three 5-HT-IR neurons in each brain ganglion, while the other species have four. A high degree of conformity in the structure of the NMS was observed, probably reflecting the close phylogenetic relationship and the similar strategy of host finding.

The neuromuscular system in freshwater furcocercaria from Belarus. II Diplostomidae, Strigeidae, and Cyathocotylidae.

The neuromuscular system (NMS) in cercariae of Diplostomum pseudospathaceum, Cotylurus szidati, Australapatemon burti, Holostephanus volgensis, and Paracoenogonimus ovatus was studied with immunocytochemical methods and confocal scanning laser microscopy. The patterns of F-actin in the musculature, 5-HT immunoreactive (-IR), FMRF-amide-IR neuronal elements, and α-tubulin-IR in sensory receptors were investigated. The NMS in the five species studied were compared with each other and with three species of Schistosomatidae studied earlier (Bilharziella polonica, Trichobilharzia szidati, and Trichobilharzia franki). No major structural differences in the musculature, the 5-HT-IR or FMRF-IR neuronal elements were noticed between the cercariae. The minor variations observed in the musculature were related to the size and organization of the muscle fibers. The checked pattern formed by the transverse muscle fibers in the tail stems of D. pseudospathaceum, C. szidati, A. burti, H. volgensis, and P. ovatus was not observed in B. polonica, T. szidati, and T. franki. A trend in the differentiation of the longitudinal muscle fibers in the furca from evenly distributed fibers in H. volgensis and P. ovatus to many bundles in D. pseudospathaceum and two well-organized lateral bundles in C. szidati, A. burti, and Trichobilharzia spp. was observed. The transverse muscle fibers in the furca follow the same trend. The number of 5-HT-IR neurons in the cercarial bodies varied between 10 and 16. In cercariae of H. volgensis and P. ovatus, the central nervous system (CNS) was less centralized compared to the CNS in the other species studied, with only two 5-HT-IR marker neurons in each brain ganglion and the other neurons distributed evenly along the main cords. In the tails of H. volgensis and P. ovatus, many transverse 5-HT-IR comissures were found. In the tails of higher strigeidid cercariae, only a few crosslinks were observed. The number and distribution of sensory receptors on the bodies and tails of the cercarial species differed from each other. A trend in the differentiation of the sensory receptors in the tails was discerned. A process of grouping and decrease in number of ciliated receptors in the stem and in the furca from H. volgensis and P. ovatus to Schistosomatid cercariae took place.

The neuro-muscular system in fresh-water furcocercaria from Belarus. I Schistosomatidae.

The neuro-muscular system (NMS) in cercariae of the family Schistosomatidae from Belarus was studied with immunocytochemical methods and confocal scanning laser microscopy. The specimens of Bilharziella polonica were compared with Trichobilharzia szidati and Trichobilharzia franki. The patterns of F-actin in the musculature, 5-HT-immunoreactive (IR), FMRFamide-IR neuronal elements and α-tubulin-IR in sensory receptors and nerves were investigated. No indications of structural differences in the musculature, the 5-HT-IR, FMRF-IR neuronal elements and the general distribution of sensory receptors were noticed between cercariae of Trichobilharzia spp. The number of 5-HT-IR neurons in the cercarial bodies is 16. In cercaria B. polonica, the tail musculature is weaker than in Trichobilharzia spp. A detailed schematic picture of the NMS in the tail of Trichobilharzia spp. cercaria is given. The function of NMS elements in the tail is discussed.

Detection of Babesia Sp. EU1 and members of spotted fever group rickettsiae in ticks collected from migratory birds at Curonian Spit, North-Western Russia.

To reveal the prevalence of spotted fever group (SFG) rickettsiae and Babesia sp. in Ixodes ricinus (L.) ticks from migratory birds, 236 specimens represented 8 species of Passeriformes and were collected at Curonian Spit in Kaliningrad enclave of North-Western Russia. The ticks (total 126) being detached from four bird species, Turdus philomelos, Fringilla coelebs, Parus major, and Sturnus vulgaris, were investigated by PCR using the primers Rp CS.877p/Rp CS.1258n for the detection of Rickettsia and BJ1/BN2 for Babesia spp. Babesia spp. were detected in 2 of 126 (1.6%) ticks. The partial sequence of 18S rDNA had 100% similarity to human pathogenic Babesia sp. EU1. The SFG rickettsiae were detected in 19 of 126 (15.1%) ticks collected from the above-mentioned bird species. BLAST analysis of SFG rickettsia gltA assigned sequences to human pathogenic Rickettsia helvetica (10.3%), Rickettsia monacensis (3.9%), and Rickettsia japonica (0.8%) with 98%-100% sequence similarity. The SFG rickettsiae and Babesia sp. EU1 in ticks collected from the passerines in Russia were detected for the first time. The survey indicates that migratory birds may become a reservoir for Babesia spp. and SFG rickettsiae. Future investigations need to characterize the role of birds in the epidemiology of these human pathogens in the region.

The neuro-muscular system in cercaria with different patterns of locomotion.

The neuro-muscular system (NMS) of cercariae with different swimming patterns was studied with immunocytochemical methods and confocal scanning laser microscopy. Specimens of the continuously swimming Cercaria parvicaudata, Maritrema subdolum and Himasthla elongata were compared with specimens of the intermittently swimming Cryptocotyle lingua and the attached Podocotyle atomon. The patterns of F-actin in the musculature, 5-HT immunoreactive (-IR), FMRFamide-IR neuronal elements, α-tubulin-IR elements in the nervous and sensory systems and DAPI-stained nuclei were investigated. The general plan of the NMS was similar in all cercariae studied. No major structural differences in the patterns of muscle fibres were observed. However, in the tail of C. lingua, transverse muscle fibres connecting the bands of longitudinal muscles were found. No major structural differences in the 5-HT- or FMRFamide-IR nervous systems were observed. The number of 5-HT-IR neurones in the cercarial bodies varied between 12 and 14. The number and distribution of the α-tubulin-IR processes on the cercarial bodies and tails differed from each other. The relation between the number and structure of the α-tubulin-IR processes and the host finding strategy of the cercariae is discussed. A detailed schematic picture of the NMS in the tails of C. lingua and M. subdolum is presented.

An immunocytochemical, histochemical and ultrastructural study of the nervous system of the tapeworm Cyathocephalus truncatus (Cestoda, Spathebothriidea).

This study is the first detailed study of the organisation of the neuromuscular system of Cyathocephalus truncatus (Cestoda, Spathebothriidea). Five techniques have been used: (1) immunocytochemistry, (2) staining with TRITC-conjugated phalloidin, (3) NADPHdiaphorase histochemistry, (4) confocal scanning laser microscopy and (5) transmission electron microscopy. The patterns of nerves immunoreactive (IR) to antibodies towards serotonin (5-HT) and the invertebrate neuropeptide FMRFamide are described in relation to the musculature. The patterns of NADPHdiaphorase positive nerves and 5-HT-IR nerves are compared. The fine structure of the nervous system (NS) is described. The organisation of NS in the non-segmented, polyzoic C. truncatus differs clearly from that in the non-segmented, monozoic Caryophyllaeus laticeps and shows distinct similarities with the NS in pseudophyllidean cestodes. This supports the hypothesis that taxon Caryophyllidea and Spatheobothriidea form independent lineages within Eucestoda.