Ultrastructure of the eye of Urastoma cyprinae (Turbellaria,Alloeocoela)

Summary Urastoma cyprinae (Graff) is a microturbellarian which has been recorded both as a free-living organism by Westblad (1955) and Marcus (1951) and as a commensal in various lamellibranch molluscs (see Burt & Drinnan 1968). The material used in this study came from oysters, Crassostroea virginica, collected off the coast of Prince Edward Island, in which hosts it occurs in large numbers especially during the summer months when the oysters are spawning (Fleming et al. 1981). When U. cyprinae is exposed to light as happens, for example, when an oyster is opened, it shows a marked negative phototactic response.Preliminary work on the fine structure of the photoreceptors in U. cyprinae shows that the two eyes each consists of: (1) a single cup cell full of relatively large, electron-dense pigment granules; (2) a tripartite conical lens system; and (3) what appear to be two photosensitive rhabdomes. The pigment cup cell has a single, well defined nucleus situated basally and close to the membrane of the pigment cell furthest away from the rhabdomeres. The lens system consists of a cone made up of three, separate but equal, parts. Each part has two, flat inner surfaces which join at an angle of 120°, an outer rounded surface, and a rounded upper surface. When these three parts fit together, the cone-shaped lens is formed with the apex of the lens within the cup of the pigment cell and the rounded, convex, broad end of the cone lying more or less at the same level as the top of the pigment cup and below the epidermis layer. The rhabdomeres lie between the electron dense lenses and the inside of the pigment cup. They show connections to the visual cells which are bipolar: one extension joining the rhabdomeres; the other constituting the axon which extends into the centrally situated brain or into the longitudinal, lateral nerves. The axons that enter the brain, form connections with other axons from the other eye. The axons that extend posteriorly in a lateral position, presumably play a role in facilitating the avoidance reaction.The chemical nature of the unusual lens has not yet been determined. This is presently under investigation and will be reported later at which time our work will be discussed in relation to other types of rhabdomeric eyes in the Turbellaria.     

Paravortex karlingi sp. nov. from Cerastoderma edule L., in Britain

Paravortex karlingi sp. nov. collected from the intestine of the bivalve mollusc Cerastorderma edule from the Ythan Estuary, N. E. Scotland, and elsewhere, is distinguished from a closely related species, P. cardii, also occurring in this host, on the basis of differences in habitat occupied by the two species as well as behavioural and morphological differences. P. karlingi is smaller, has fewer embryos in the gravid adult and shows a different behaviour pattern when released from the host intestine. It is also negatively phototactic whereas P. cardii is initially positively phototactic, only later becoming negatively phototactic. The occurrence of both species in Britain is briefly described.Abbreviations bc brood capsules - c core of indigestible particles - ca common atrium - ch chamber - e eye - fa female atrium - fol fibre optic light - gc gut caecum - gp genital pore - j juvenile worm - m mouth - o ovary - oe oesophagus - p pharynx - pe penis - sg shell gland - sv seminal vesicle - t testis - u uterus - vg vitelline gland - w window     

The karyotypes of Dugesia species from Spain (Turbellaria,Tricladida)

Some species of Planarians, new to Spain, are recorded. Dugesia polychroa, D. sicula, D. iberica and D. gonocephala s. 1. have been investigated karyologically. The former possesses a diploid complement characteristic of the biotype A (2n = 8); the second is diploid with 2n = 18; diploidy and triploidy were found in sexual populations of D. iberica with n = 8. Triploidy occurred in all the asexual strains of the D. gonocephala group with a basic number of either 8 or 9. In this latter case B-chromosomes were occasionally found.     

Ultrastructure of the copulatory stylet and accessory spines in Haplopharynx quadristimulus (Turbellaria)

The copulatory organ of Haplopharynx quadristimulus Ax, 1971 (Carolina form, Rieger, 1977) consists of a proximal prostatic vesicle and a distal stylet apparatus comprising a central tubular stylet and four to five peripheral accessory spines. By electron microscopy it could be seen that the stylet and spines were intracellular specializations. The copulatory organ can be interpreted as a specialization of an epithelial canal extending from the testes to the body wall. In the complex stylet apparatus, the epithelium was differentiated into six cell types. The stylet, which was formed in a matrix syncytium next to the prostatic vesicle, extended into the lumen of the stylet canal. The interior of the stylet apparatus contained one group of cells that had thick ciliary rootlets and another that had rootlet-like ribbons.The cells that contain the rootlets enveloped bundles of longitudinally arranged muscles. The accessory spines were formed in cells which lay peripheral to the muscle bundles. The spines, stylet, rootlet-like ribbons, and rootlets had similar patterns of periodic cross striations. The similarity in striation patterns suggests that the accessory spines and stylet are composed of modified ciliary rootlets.     

Ultrastructural observations on gastrodermal regeneration in the planarian Dugesia japonica (Turbellaria)

The earliest detectable change during regeneration of the gastrodermis in Dugesia japonica was an aggregation of regenerative cells underneath the gastrodermis remaining at the wound margin. The gastrodermal cells in experimental regenerates retained some of their original characters and presented no indication of cell dedifferentiation. The regenerative cells came into contact with the basal surface of gastrodermal cells, forming stratified cell layers. Differentiation of these cells into gastrodermal cells was initiated by the development of synthetic organelles within their cytoplasm. These differentiating cells gave rise to two different types of gastrodermal cells, namely phagocytic cells and sphere cells. In later stages, there was an apparent movement of differentiated gastrodermal cells towards the parenchyma.     

Ultrastructural features of the epidermis of the planarian Artioposthia triangulata (Dendy)

The epidermis of the land planarian Arthioposthia triangulatawas examined by scanning and transmission electron microscopy. Thisinvestigation revealed that the flatworm was covered entirely withcilia and was especially densely populated on the ventral surface.In all regions the epidermis consisted of a one-layered columnarepithelium resting on a prominent basement membrane, but lacking aterminal web. Various secretions were found in the epidermistogether with epidermal rhabdoids. Below the basement membraneother secretory material was visible and this included thecytoplasmic lamellated granules and adenal rhabdites. The basementmembrane consisted of fibrils with a beaded appearance and thesewere arranged parallel to the epidermal layer but did not displaycross-banding. The secretory cells above and below the basementmembrane were compared and their products characterized on thebasis of shape, size and location. Their possible function isdiscussed.     

Frontal organs in the Acoelomorpha (Turbellaria): Ultrastructure and phylogenetic significance

Using characters discernible through electron microscopy, we redefine the organ traditionally identified as the frontal organ in acoelomorph turbellarians as being a collection of two to several large mucus-secreting glands whose necks emerge together through a frontal pore at the exact apical pole of the body, i.e. at the point where the pattern of epidermal ciliary rootlets converges. Representatives that we have studied of each of the acoel families Paratomellidae, Diopisthoporidae, Solenofilomorphidae, Convolutidae, Otocelidae, and Mecynostomidae, as well as a representative of the Nemertodermatida, have such glands. Up to five additional types of glands that open anteriorly outside of the frontal pore, some of which are indistinguishable from glands of the general body wall, could be seen in the nemertodermatid, in Hesiolicium inops (Paratomellidae), and in representatives of the latter four acoel families. In Paratomella, three different types of glands open in diffuse fashion in a frontal glandular complex reminiscent of that in the Macrostomida.Sensory elements near the frontal pore appear to be independent of the gland necks, and so the organ cannot be considered a sensory organ.The frontal organ, as described above, appears very likely to be homologous within the Acoelomorpha, and represents another strong (although unrooted) autapomorphy for this line of turbellarian evolution.     

Structure and maintenance of the epidermis in Friedmaniella sp. (Prolecithophora)

The epidermis of Friedmaniella sp. has been studied using light and electron microscopy. Three main morphological features characterize its cells, namely (1) DNA bodies in the nuclei, (2) an extensive Golgi apparatus with a well-developed system of transport vesicles, (3) clusters of centrioles mainly in the basal cytoplasm and axonemes and rootlets in the middle and apical cell parts. These peculiarities may indicate continuous physiological regeneration within the cell at the level of cell organelles. DNA bodies may prove to be a taxonomic feature distinguishing the Prolecithophora from other turbellarians.     

The geographical and bathymetrical distribution of the Fecampiidae (Turbellaria,Rhabdocoela)

All members of the Fecampiidae are endoparasites. Since 1964 when only four species were known, four new species and 11 cocoon types, made by as many unknown species, have been described.The Fecampiidae are distributed in all major oceans from shallow waters to more than 5000 m depth.     

The ultrastructure of the eyes of<Emphasis Type="Italic"> Paravortex karlingi</Emphasis> (Plathelminthes,Rhabdocoela)

Both eyes of Paravortex karlingi belong to the rhabdomeric type. Each eye consists of a single pigment cup cell and three sensory cells. Modified mitochondria lie in three protrusions of the cup cell, and several of these mitochondria form giant mitochondrial derivates. The centres of the derivates include electron-dense substances. These modified structures may have lenticular functions. Furthermore, it is shown that giant mitochondrial derivates develop by fusion of smaller ones. Embryos have many small mitochondria in the developing eyes whereas the adult possesses less numerous, but giant forms. This circumstance leads to the assumption that all such lenticular structures within the rhabdocoels result from identical processes.     

Taxonomic studies on marine triclads (Turbellaria,Tricladida, Maricola)

The genus Procerodes forms a heterogeneous assemblage of taxa. Although it is premature to attempt phylogenetic weighting of the characters, the genus contains three well delimited subgroups, one with a subantarctic, panaustral distribution, one world-wide in distribution, and one occurring principally in the northern hemisphere. Outside of these subgroups, species in this genus are problematic since a number of their features also occurs in other procerodids. All recognized groups exhibit a wide distributional range. Many of the world-wide taxonomic relations lie on the species level and some at the level of genera. Poor dispersal capacity of extant species of Procerodes suggests that the biogeographic patterns may be very old.     

Distribution,abundance, and size of rhabdoids in Dugesia polychroa. (Turbellaria: Tricladida)

The ontogenetic changes in the distribution, abundance, and size of rhabdoids were examined in an undisturbed laboratory population of Dugesia polychroa. Irrespective of triclad age, rhabdoids in the epidermis and parenchyma were more abundant on the dorsal than the ventral side of the body. No significant differences were found in the abundance of epidermal or parenchymal rhabdoids among the anterior, medial, and posterior regions of the body. Rhabdoid number and size changed significantly with triclad age, with a marked depression coinciding with the onset of cocoon production. Rhabdoid discharge was correlated with physical and/or physiological disturbance and occurred in the absence of any overt environmental disturbance. Simple allometric relationships were observed between rhabdoid size and number on one hand and body plan area on the other. Different allometric trends were observed from field-collected individuals compared to the undisturbed laboratory population. The potential function of rhabdoids in the Tricladida is discussed in light of these findings.     

Predation potential of three flatworm species (Platyhelminthes: Turbellaria) on mosquitoes (Diptera: Culicidae)

We conducted a field survey for flatworms to select species as potential biological control agents against Aedes aegypti and Culex pipiens (Diptera, Culicidae) breeding in artificial containers. Laboratory experiments were performed to determine the daily predation rate, differential predation on each mosquito larval instar, selective predation on either A. aegypti or C. pipiens, and predator tolerance to water from artificial containers. Girardia anceps (Tricladida, Paludicola, Dugesiidae), Mesostoma ehrenbergii and Bothromesostoma cf. evelinae (Rhabdocoela, Typhloplanoida, Typhloplanidae) were found in temporary puddles and permanent pools. In the laboratory, they killed between 52% and 100% of immature mosquitoes coexisting in the same habitat. No preference of flatworms for mosquito preys was detected. Predation rate was related to predator size and instar of preys. Girardia anceps and B. evelinae survived after a dry period and when re-flooding occurred, they laid eggs. Tolerance to water from artificial containers was highest in G. anceps and this species could be a suitable predator to reduce mosquito populations from artificial containers using an inoculative approach.     

Ultrastructure of epidermal eyespots of Microstomum lineare (Turbellaria,macrostomida)

Summary The eyespots of Microstomum lineare were studied by electron microscopy, light microscopy, and fluorescence microscopy. Each eyespot consists of two ciliary photoreceptor cells shielded by pigment cells and additional sensory cells. The photoreceptor cells are characterized by a distal intracellular cavity lined with 50–100 interwoven cilia. The other sensory cells are of two ultrastructurally different types, one with long cilia predominating and the other with balloonlike cilia. The pigment cells, which envelop processes of the sensory cells, contain pigment vacuoles varying in size and content and give a bright red fluorescence by the Falck-Hillarp method. The eyespots are suggested to perform a dual function as photoreceptors and chemoreceptors. The evolutionary significance of ciliary photoreceptors in Turbellaria is discussed.     

Immunoreactivity to a specific echinoderm neuropeptide in the nervous system of the flatworm Macrostomum hystricinum marinum (Turbellaria,Macrostomida)

Immunocytochemical characterization of the neuropeptides FMRF-amide and serotonin (5-HT) is a well-known method successfully applied to demonstrate nervous-system morphology in several platyhelminths (see Wikgren & Reuter, 1985, and Reuter, 1988, for review). We have immunolabeled whole-mount preparations of Macrostomum hystricinum marinum Rieger from cultures (see Rieger et al., 1988) with anti-SALMF-amide, an antibody specific for the C-terminal pentapeptide sequence of the neuropeptide GNFSALMF-amide recently isolated from echinoderms (source M. Thorndyke, England). Immunoreactivity to SALMF-amide gave a more detailed picture of the nervous system of M. hystricinum than FMRF-amide. Conventional light microscopy (Luther, 1905) shows this nervous system to consist of a bilobed brain, a pharyngeal nerve-ring system, a posterior commissure, and two main ventrolateral nerve cords. Immunostaining reveals, in addition, two thin paired longitudinal nerve strands and fine subepithelial and submuscular nerve nets. Anti-SALMF-amide labels a distinct class of neurons, causing the main lateral longitudinal cords and pharyngeal nerve-ring system to appear more filamentous than with other techniques. Recent fine-structural investigations on the nervous system of Macrostomum hystricinum marinum revealed several axon types with characteristic vesicles and neurotubules (D. R. pers. obs.). Partly supported by FWF grant P7816.     

An ultrastructural and cytochemical study of the digestive system in Oxyposthia praedator (Turbellaria,Acoela)

The central parenchyma in Oxyposthia praedator consists of multifunctional cells. These cells digest food material intracellularly, can effect extracellular digestion through release of digestive enzymes by cell lysis and clasmatosis, and synthesize reserve nutritional substances.     

Ultrastructural observations on paracnids. I: Coelogynopora axi Sopott (Turbellaria,Proseriata)

The Schlauchdrüsen or paracnids of Coelogynopora axi Sopott, 1972 consist of two components: a muscle cell and a secretory cell.The secretory cell is provided with a tube, which bears a border of microvilli. In the normal position the tube is situated in the interior of the secretory cell, and the microvilli stand at the inner side of the tube. After expulsion of the tube the microvilli are situated at its free surface.The evagination takes place in response to chemical stimuli and is effected by the contraction of the myofibrils of the muscle cell.The paracnids are supposed to be mechanisms of defense.However, conformities with nematocysts and spirocysts of the cnidarians do not exist.The paracnids in other species of the Coelogynoporidae, for example in Invenusta paracnida (Karling, 1966) and Carenscoilia bidentata Sopott, 1972 differ from those of C. axi in many details.Abbreviations bl- basement lamina - ep- epidermis - hd- hemidesmosomes - mc- muscle cell - mt- microtubules - mv- microvilli - nsc- nucleus of the secretory cell - sb- bowl containing secretion granules - sc- secretory cell - sd- septate desmosome-like structures - sg- secretion granules - t- tube - tf- tonofilaments     

Observations on the ultrastructure of the copulatory organ of Archilopsis unipunctata (Fabricius, 1826) (Proseriata,Monocelididae)

The copulatory organ in adult specimens of Archilopsis unipunctata has been studied by transmission electron microscopy.This copulatory organ is of the conjuncta-duplex type with eversible cirrus. The seminal vesicle, lined with a nucleate epithelium, is surrounded by spirally arranged muscles. The fibres are enclosed in a sheath that is continuous with the septum of the bulbus and the basement lamina of the male canal epithelium. Distally to the seminal vesicle the bulbus is filled with the secretory cell-necks of the prostate glands. The male canal shows three different parts: seminal duct, ejaculatory duct and eversible cirrus. At the transition of seminal duct and ejaculatory duct two prostate ducts open into the lumen. The structure of the epithelium lining the different parts of the canal is described. The transition into the cirrus may be recognized by an abrupt change in the thickness, the electron density and the stratification in the basement lamina and by the disappearance of the epithelium absent indeed in the cirrus. The material found inside the cirrus-lumen is different according to the zone considered. The origin of this material and of the cirrus teeth is discussed.Abbreviations ab- apoptotic body - ba- bacteria - bb- basal bodies of cilia - bl- basement lamina - bw- body wall - c- cilia - cb- cell body - cgp- common genital porus - ci- cirrus - cip- cirrus plug - cl- lumen of cirrus - cm- circular muscles - cr- cytoplasmatic remnants - cs- cytoplasmatic sheets - ejd- ejaculatory duct - ep_ej- epithelium of ejaculatory duct - d- desmosomes - f- flagella of spermatozoa - fd- female duct - fp- female porus - gc- golgi complex - gl- glycogen particles - hd- hemidesmosomes - lm- longitudinal muscles - ly- lysosome-like body - m- muscles - m_b- muscles of the bulbus - m_c- muscles of the cirrus - m_c- muscles of the seminal vesicle - mi- mitochondria - ml- microvilli - ms- mesenchyme - n_sd- nuclei of the seminal duct - pd- prostate duct - pg- prostate glands - ri- ribosomes - s- septum - sb- secretory vesicle - sd- seminal duct - sp- spines - sv- seminal vesicle - v- vagina - vd- vas deferens     

Ultrastructure and wear patterns of the ventral epidermis of four snake species (Squamata,Serpentes)

Snakes are limbless tetrapods highly specialized for sliding locomotion. This locomotion leads to the skin being exposed to friction loads, especially on the ventral body side, which leads to wear. It is presumed that snakes therefore have specific optimizations for minimizing abrasion. Scales from snakes with habitat, locomotor and/or behavior specializations have specific gradients in material properties that may be due to different epidermal architecture. To approach this issue we examined the skin of Lampropeltis getula californiae (terrestrial), Epicrates cenchria cenchria (generalist), Morelia viridis (arboreal), and Gongylophis colubrinus (burrowing) with a focus on (i) the ultrastructure of the ventral epidermis and (ii) the qualitative abrasion pattern of the ventral scales. Scanning and transmission electron microscopy revealed variations in the structure, thickness, layering, and material composition of the epidermis between the species. Furthermore, SEM and white light interferometer images of the scale surface showed that the abrasion patterns differed, even when the snakes were reared on the same substrate. These data support the idea that (i) a specific gradient in material properties may be due to a variation in epidermis architecture (thickness/ultrastructure) and (ii) this variation may be an optimization of material properties for specific ways of life.