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Diplozoidae (Monogenea) are blood-feeding freshwater fish gill ectoparasites with extraordinary body architecture and a unique sexual behaviour in which two larval worms fuse and transform into one functioning individual. In this study, we describe the body organisation of Paradiplozoon homoion adult stage using a combined approach of confocal laser scanning and electron microscopy, with emphasis on the forebody and hindbody. Special attention is given to structures involved in functional adaptation to ectoparasitism, i.e. host searching, attachment and feeding/metabolism. Our observations indicate clear adaptations for blood sucking, with a well-innervated mouth opening surrounded by sensory structures, prominent muscular buccal suckers and a pharynx. The buccal cavity surface is covered with numerous tegumentary digitations that increase the area in contact with host tissue and, subsequently, with its blood. The buccal suckers and the well-innervated haptor (with sclerotised clamps controlled by noticeable musculature) cooperate in attaching to and moving over the host. Putative gland cells accumulate in the region of apical circular structures, pharynx area and in the haptor middle region. Paired club-shaped sacs lying laterally to the pharynx might serve as secretory reservoirs. Furthermore, we were able to visualise the body wall musculature, including peripheral innervation, the distribution of uniciliated sensory structures essential for reception of external environmental information, and flame cells involved in excretion. Our results confirm in detail that P. homoion displays a range of sophisticated adaptations to an ectoparasitic life style, characteristic for diplozoid monogeneans.

There is little evidence that the already described and accepted taxa of ascarids (Ascaris lumbricoides, A. suum, and A. ovis) infecting individuals of taxonomically distant groups (hominids, pigs, sheep, goats, and dogs) can be genetically or morphologically distinguished. However, despite described morphological differences, e.g., due to intraspecific variation, these are insufficient for species determination and may indicate differences amongst ascarids because of cross infections, hybrid production, and specific adaptations to hosts. Herein, the results of a molecular and morphological analysis of ascarids parasitising Sumatran orangutans (Pongo abelii Lesson, 1827) in native populations are presented. The research took place in the Bukit Lawang area, Indonesia, in 2009. Throughout the year, fresh faecal samples were collected regularly from 24 orangutans, and all were examined for the presence of nematode adults. Only five adult worms from two orangutan females were found during regular collection. Using the integrative taxonomic approach, the nematodes found were identified as A. lumbricoides. The significance of the find and its rarity is documented by the fact that this is the first confirmed finding of adult ascarids from an original orangutan site (not from a zoo) in more than 130 years (including the long-term study spanning the last 20 years focusing on orangutan parasites and natural antiparasitic drugs). More accurate morphometric parameters and genetic differences for the identification of ascarids were established. These parameters will be helpful for other findings in great apes and will also be suitable for further and precise determination of this parasite. The details distinguishing between male and female specimens are also stated and well defined. A comprehensive evaluation of the situation of Ascaris species parasitising orangutans, including a comparison with previously described orangutan parasite (i.e., A. satyri—species inquirenda), is discussed.

Background Monogeneans, in general, show a range of unique adaptations to a parasitic lifestyle, making this group enormously diverse. Due to their unique biological properties, diplozoid monogeneans represent an attractive model group for various investigations on diverse biological interactions. However, despite numerous studies, there are still gaps in our knowledge of diplozoid biology and morphofunctional adaptations. Results In this study, we provide a comprehensive microscopic analysis of systems/structures involved in niche searching, sensing and self-protection against the host environment, and excretory/secretory processes in Eudiplozoon nipponicum . Freeze-etching enabled us to detect syncytium organisational features not visible by TEM alone, such as the presence of a membrane subjacent to the apical plasma membrane (separated by a dense protein layer) and a lack of basal plasma membrane. We located several types of secretory/excretory vesicles and bodies, including those attached to the superficial membranes of the tegument. Giant unicellular glands were seen accumulating predominantly in the apical forebody and hindbody haptor region. Muscle layer organisation differed from that generally described, with the outer circular and inner longitudinal muscles being basket-like interwoven by diagonal muscles with additional perpendicular muscles anchored to the tegument. Abundant muscles within the tegumentary ridges were detected, which presumably assist in fixing the parasite between the gill lamellae. Freeze-etching, alongside transmission electron and confocal microscopy with tubulin labelling, enabled visualisation of the protonephridia and nervous system, including the peripheral network and receptor innervation. Three types of receptor were identified: 1) uniciliated sensory endings with a subtle (or missing) tegumentary rim, 2) obviously raised uniciliated receptors with a prominent tegumentary rim (packed with massive innervation and muscles) and 3) non-ciliated papillae (restricted to the hindbody lateral region). Conclusions This study points to specific morphofunctional adaptations that have evolved in diplozoid monogeneans to confront their fish host. We clearly demonstrate that the combination of different microscopic techniques is beneficial and can reveal hidden differences, even in much-studied model organisms such as E. nipponicum .

There is little evidence that the already described and accepted taxa of ascarids (Ascaris lumbricoides, A. suum, and A. ovis) infecting individuals of taxonomically distant groups (hominids, pigs, sheep, goats, and dogs) can be genetically or morphologically distinguished. However, despite described morphological differences, e.g., due to intraspecific variation, these are insufficient for species determination and may indicate differences amongst ascarids because of cross infections, hybrid production, and specific adaptations to hosts. Herein, the results of a molecular and morphological analysis of ascarids parasitising Sumatran orangutans (Pongo abelii Lesson, 1827) in native populations are presented. The research took place in the Bukit Lawang area, Indonesia, in 2009. Throughout the year, fresh faecal samples were collected regularly from 24 orangutans, and all were examined for the presence of nematode adults. Only five adult worms from two orangutan females were found during regular collection. Using the integrative taxonomic approach, the nematodes found were identified as A. lumbricoides. The significance of the find and its rarity is documented by the fact that this is the first confirmed finding of adult ascarids from an original orangutan site (not from a zoo) in more than 130 years (including the long-term study spanning the last 20 years focusing on orangutan parasites and natural antiparasitic drugs). More accurate morphometric parameters and genetic differences for the identification of ascarids were established. These parameters will be helpful for other findings in great apes and will also be suitable for further and precise determination of this parasite. The details distinguishing between male and female specimens are also stated and well defined. A comprehensive evaluation of the situation of Ascaris species parasitising orangutans, including a comparison with previously described orangutan parasite (i.e., A. satyri—species inquirenda), is discussed.

A West African species of gecko, Tarentola parvicarinata Joger (Gekkonidae), collected in the Niokolo Koba National Park in East Senegal is a new host species for the nematode Parapharyngodon echinatus (Rudolphi, 1819). Fifty one specimens of P. echinatus were studied under a light microscope and thirteen specimens were studied for the first time by a scanning electron microscope. The main differences between P. echinatus and other African species, especially Parapharyngodon micipsae (Seurat, 1917), were in the shape of annules on body cuticle, broad lateral alae and their terminations, the shape of the distal extremity of the spicule and number of outgrowths at the anterior cloacal lip. For the purposes of DNA characterization, partial sequence of the small subunit ribosomal RNA gene (SSU rRNA) was obtained from two specimens of P. echinatus . This is the first published sequence of a species from the family Pharyngodonidae.