Haptoral neuromusculature in two species of Dactylogyrus Diesing, 1850 (Monogenea: Dactylogyridae)

The pharyngeal and genitalia-associated muscles of Rhabditolaimus ulmi (Nematoda: Chromodorea: Rhabditida: Diplogastridae)

The copulatory organs and pharynx are important for nematode classification. This research aimed to study the musculature of the wood-inhabiting nematode, Rhabditolaimus ulmi, using confocal microscopy. The lip region is hexagonal with enlarged lateral lips; the pharynx is diplogastrid type with two bulbs. The corpus comprises the fused stegostoma, procorpus and metacorpus, with six glands opening in the stegostoma and the corpus limen. The stegostoma has a large dorsal bulge and the posterior bulb is devoid of valve, with two circles of dilators and a basal sphincter. The female genital muscles have a four-radial symmetry around the vaginal opening to the uterus. Two vaginal constrictors and four pairs of dilators of two types are connected to the vagina-uterus opening; four dilators run perpendicular to the uterus axis and are connected to the uterine muscular corset. The sphincter between the intestine and cloaca consists of the middle ring with two pairs of processes connected ventrally with intestinal fasciculi and dorsally with the body wall. The ring contains the inner biconical X-structure. In the male, the gubernaculum has the dorsal erector and a pair of transverse muscles. The wide gubernacular spicule protractor envelops spicules anteriorly. The ventral tail muscle is wide, unpaired, and nine pairs of serial diagonal muscles are located beneath the body wall muscles, followed by three pairs of postcloacal oblique muscles of the tail. Anal depressors comprise a pair of transverse muscles with expanded middle globular parts. The copulatory muscles are of the Rhabditidae and Cephalobidae type modified because of spicules elongation. The muscle characters code of the previously published tabular key for 15 muscle characters is 73422-22144-42223; it can be used for phylogenetic reconstructions.

Neuromuscular organization and haptoral armament of Polyclithrum ponticum (Monogenea: Gyrodactylidae)

Most gyrodactylids have a haptor armed with a pair of hamuli, two connecting bars and 16 marginal hooks. In some gyrodactylids, however, the haptor is disc-shaped and reinforced by additional sclerites. The genus Polyclithrum has arguably the most elaborate haptor in this group. This study aimed to gain better understanding of the anatomy of Polyclithrum by examining neuromusculature and haptoral armament of Polyclithrum ponticum, a species parasitizing Mugil cephalus in the Black Sea, with emphasis on haptoral sclerites and musculature in connection with host-attachment mechanisms. Musculature was stained by phalloidin, the nervous system by anti-serotonin and anti-FMRFamide antibodies, and haptoral sclerites were visualized in reflected light. The study provided new information on sclerites: in addition to previously described supplementary sclerites (A1-6), ear-shaped sclerites (ESSs) and two paired groups of ribs, reflected light revealed a rod-shaped process on the ESSs and a pair of small posterior sclerites. The sclerites were shown to be operated by 16 muscles, the most prominent of which were two transverse muscles connecting the hamular roots, three muscles attached to sclerite A2, the muscle fibres of anterior ribs and a set of extrinsic muscles. The nervous system consists of a pair of cerebral ganglia connected by a commissure and three pairs of nerve cords that unite in the haptor to form a loop between the opposite cords. The arrangement of sclerites and muscles suggests that Polyclithrum initiates the attachment by clamping a host's surface with longitudinally folded haptor and then secures its position with marginal hooks.

Muscles of the male and female copulatory organs of Bursaphelenchus mucronatus and Chiloplacus sp. (Nematoda: Rhabditida)

Male and female copulatory organs figure prominently in nematode taxonomy, but the associated musculature remains insufficiently explored. The aim of this study was therefore to further our knowledge of the musculature of the vulva and male copulatory organs in nematodes by using phalloidin staining and confocal microscopy to examine two nematode species, Bursaphelenchus mucronatus and Chiloplacus sp. The musculature of the round vulva in Chiloplacus sp. comprises three pairs of radial vulval dilators and another pair of dilators of the anterior inner vulval plate. This arrangement is similar to that of the Rhabditida, but in Chiloplacus the anterior pair appears to have been transformed into the vulval plate muscles. The musculature of the slit-like vulva in B. mucronatus includes dilators of the vulval lips and external vulval flap, constrictors of the vulval slit and posterior transverse muscle bands. The opposing pairs of vulval dilators show quadrilateral symmetry as observed in the Rhabditida, but the constrictors running along the rim of the vulva have no counterparts in other species. The musculature of the male copulatory organ in Chiloplacus sp. comprises two pairs of spicule protractors and retractors and three pairs of gubernacular muscles. In B. mucronatus, as in the other Aphelenchoididae, the gubernaculum is absent and there is one pair of spicule protractors and two pairs of muscles inserted on the saddle (angular bend) of the spicules. The arrangement of the spicule saddle muscles resembles those of the gubernaculum, which may indicate that in this family the gubernaculum has become fused to the spicules. The literature review of muscles of nematode copulatory organs are given in a table for 15 muscle groups; it can be used for phylogenetic reconstruction and classification of the order Rhabditida.

First evidence of serotoninergic components in the nervous system of the monogenean Chimaericola leptogaster (Chimaericolidae, Polyopisthocotylea), a gill parasite of the relict holocephalan fish

The localisation and distribution of the serotoninergic nerve elements was studied for the first time in the flatworm Chimaericola leptogaster (Leuckart, 1830) using immunocytochemical methodology and confocal laser scanning microscopy. The musculature was investigated by histochemical staining of actin filaments; scanning electron microscopy was used to identify the sensory structures on the worm's surface. Uniciliated, bi-ciliated and multiciliated sensory endings have been described on the worm's surface. The morphological data demonstrate the presence of circular, longitudinal and diagonal muscles that comprise the musculature of C. leptogaster in the anterior, median and posterior body regions. Well-developed radial and circular muscle fibres were also observed surrounding the genital pore, two vaginae and in clumps of the haptor. The study revealed the presence of biogenic amine, serotonin, in the central and peripheral nervous systems of C. leptogaster: in the neurons and fibres of the cephalic ganglia and ventral nerve cord, in the innervation of reproductive system compartments. The localised sites of the serotoninergic elements point to important roles of serotonin in monogenean reproductive processes and, possibly, in the regulation of muscle function.

Muscular Arrangement and Sclerite Morphology in the Haptor of Tetraonchus monenteron (Monogenea, Dactylogyridea)

BACKGROUND : Tetraonchidae is a small and relatively monomorphic family of dactylogyroid monogeneans. Since the morphology of sclerites of the attachment organ (haptor) is one of the primary criteria in tetraonchid taxonomy, the confocal study of sclerites and associated musculature may provide valuable taxonomic information. PURPOSE : The aim of this study was to examine the haptoral sclerites and musculature in Tetraonchus monenteron (Wagener, 1857), a common parasite of pike.

METHODS

Haptoral musculature of T. monenteron was studied using phalloidin staining and confocal microscopy, with sclerites visualized in the reflection confocal mode.

RESULTS

Haptoral armature of T. monenteron consists of ventral and dorsal pairs of anchors, a ventral bar, eight pairs of marginal hooks and at least three pairs of accessory sclerites. Anchors are operated by 14 muscles, of which the most prominent are extrinsic muscles, the transverse muscle interconnecting the ventral anchors, three muscles connecting the ventral anchor to the ventral bar, and four muscles of the dorsal and ventral anchors inserting on the haptoral wall. The extrinsic muscles are attached to the braceshaped sclerites, which in turn are connected to the dorsal anchors via muscle bundles.

CONCLUSION

The gaffing action of the dorsal anchors is likely to be achieved by the extrinsic muscles and the transverse muscle that clamps the extrinsic muscles against the body wall. The ventral anchors are probably held in attached position by the transverse muscle and four muscles inserting on the ventral bar and haptoral wall. The haptoral musculature may have potential utility for tetraonchid taxonomy.

Evolutionary modularity and morphological integration in the haptoral anchor structures of Ligophorus spp. (Monogenea: Dactylogyridae)

An important question in the study of phenotypic evolution is whether characters are independent of each other or behave and evolve as integrated modules. Morphological integration and modularity provide a powerful framework for the analysis of the evolution of morphological traits. We used geometric morphometrics and phylogenetically independent contrasts (PIC) to test four different modularity hypotheses in the haptoral anchors of 14 monogenean species of Ligophorus. Integration between the modular units identified was further evaluated with two-block partial least squares analysis. Roots and points represented two modules in the dorsal and ventral anchors, but modularity was not statistically supported when parasite phylogeny was accounted for, which may indicate convergent evolution related to host characteristics and gill morphology. In contrast, PIC revealed medial and lateral modules in ventral anchors only. Moreover, we found evidence for ventral and dorsal anchor pairs forming two modules, supporting the notion that they play different functional roles. Integration between all identified modules was strong. We conclude that there is modular structure in the anchors of Ligophorus spp., accounted by adaptive and phylogenetic factors acting at different levels, and ventral and dorsal anchors evolve as integrated modules with specific roles in attachment.