Redescription of Aspidogaster limacoides Diesing, 1834 (Aspidogastrea: Aspidogastridae) from freshwater fishes of northern Germany.

Aspidogaster limacoides Diesing, 1834 (Aspidogastridae) is redescribed based on light and scanning electron microscopy of specimens from the stomach and intestine of Abramis brama, Rutilus rutilus and Scardinius erythrophthalmus (Actinopterygii: Cyprinidae). The fishes were sampled during 2018 and 2019 at Lake Tollense in Mecklenburg-Western Pomerania, Germany. The prevalence of A. limacoides was highest in R. rutilus (61.7%) followed by Scardinius erythrophthalmus (7.7%) and A. brama (2.9%), while it was absent in Perca fluviatilis from the same lake. The following structures of A. limacoides are described for the first time: a depression on the ventral side of the neck, variations in the number and the arrangement of alveoli, numerous pits scattered all over the body surface, the presence of a few papillae-like structures posterior lateral to the mouth, the number of marginal organs represented by openings of exocrine multicellular glands as shown in histology and the subterminal position of the excretory pore. These characters can be used to distinguish three species of Aspidogaster, namely, A. ijimai, A. conchicola and A. limacoides, suggesting that SEM is a useful and promising tool in differentiating Aspidogaster species. Comparison of molecular data of the ITS1-5.8S-ITS2 regions showed a 94% similarity to A. limacoides from the European part of Russia. Phylogenetic analysis showed that the present specimens clustered in the same clade with A. limacoides sensu stricto, forming a distinct group to the exclusion of congeners.

Otobothrium muscatense n. sp. (Trypanorhyncha: Otobothriidae) from Rhabdosargus sarba (Forsskål) (Sparidae), with new locality records of larval trypanorhynchs off the Sultanate of Oman.

In the evaluation of the larval trypanorhynch fauna off the Sultanate of Oman, a total of 188 bony fishes belonging to 16 species were studied, which led to the description of a new species with the establishment of new host and locality records. A new otobothriid species, Otobothrium muscatense n. sp., is described from Rhabdosargus sarba (Forsskål). Based on scolex morphology and tentacular armature, the new species closely resembles the small-sized Otobothrium Linton, 1890 species described as Otobothrium cysticum (Mayer, 1842) and O. crenacolle Linton, 1890. However, it differs from them in the basal armature by a more robust shape of the first principal and the triangular shape of the billhooks as well as by the retractor muscle originating in the posterior part of the tentacle sheath, attaching to a thickening of the tentacle sheath wall, with a muscular branch continuing and attaching at front part of the bulb. It differs from the other species of Otobothrium by size, the combination of six principal hooks and a single intercalary hook in the metabasal armature, and the plane of reflection through the tentacle surfaces. New locality records of the tentaculariids Nybelinia indica Chandra, 1986, Heteronybelinia yamagutii (Dollfus, 1960), Tentacularia coryphaenae Bosc, 1797, and Mixonybelinia lepturi Palm, 2004, together with the lacistorhynchids Pseudogrillotia multiminacantha Palm, 2004 and Callitetrarhynchus gracilis (Rudolphi, 1819), and the pseudotobothriid Parotobothrium balli (Southwell, 1929) off the Muscat region are established. Of the reported species, especially P. multiminacantha and M. lepturi occurring in Trichiurus lepturus L. further demonstrate the relatedness between the Indonesian and the northwestern Indian Ocean fauna, increasing the number of joint records between Indonesia and Omani waters to 14 species.

Glyphidohaptor safiensis n. sp. (Monogenea: Ancyrocephalidae) from the white-spotted rabbitfish Siganus canaliculatus (Park) (Perciformes: Siganidae) off Oman, with notes on its phylogenetic position within the Ancyrocephalidae Bychowsky & Nagibina, 1968 (sensu lato).

A new ancyrocephalid monogenean is described from the gills of wild White-spottedrabbitfish Siganus canaliculatus (Park) based on morphological and molecular analyses. Glyphidohaptor safiensis n. sp. can be distinguished from other members of the genus by the shape of the accessory piece of the male copulatory organ (MCO). Unlike its congeners, the rod-shaped accessory piece of G. safiensis n. sp. is distally broad and flattened. The MCO of G. safiensis n. sp. is curved, enclosed in a heavy sheath with a terminal flap. Partial large subunit (LSU), partial small subunit (SSU) and the partial SSU, entire internal transcribed spacer region 1 (ITS1) and partial 5.8S rDNA of the new species and two species of Tetrancistrum Goto & Kikuchi, 1917 from the same host and locality were sequenced and subjected to phylogenetic analysis. The LSU rDNA analysis grouped G. safiensis n. sp. with Tetrancistrum sp. from the gills of Siganus fuscescens Houttuyn from Australia, indicating a possible misidentification of the latter. Sequences of the SSU rDNA of the new species were most similar to those for Pseudohaliotrema sphincteroporus Yamaguti, 1953, demonstrating the close relatedness of the genera Pseudohaliotrema Yamaguti, 1953 and Glyphidohaptor Kritsky, Galli & Yang, 2007 within the Ancyrocephalidae. The comparison of the partial SSU (424 bp) and entire ITS1 and partial 5.8S rDNA (246 bp) sequences obtained for G. safiensis n. sp. with the only available sequence of another member of Glyphidohaptor Kritsky, Galli & Yang, 2007, G. pletocirra Paperna, 1972 (HE601931-HE601933) yielded on average 1.08% dissimilarity (a difference of 7 bases), with a p-distance of 0.010 ± 0.004%. This is the first record of a species of Glyphidohaptor from S. canaliculatus and from the Persian Gulf, the Gulf of Oman and the Arabian Sea.

Pseudempleurosoma haywardi sp. nov. (Monogenea: Ancyrocephalidae (sensu lato) Bychowsky & Nagibina, 1968): An endoparasite of croakers (Teleostei: Sciaenidae) from Indonesia.

An endoparasitic monogenean was identified for the first time from Indonesia. The oesophagus and anterior stomach of the croakers Nibea soldado (Lacépède) and Otolithes ruber (Bloch & Schneider) (n = 35 each) sampled from the South Java coast in May 2011 and Johnius amblycephalus (Bleeker) (n = 2) (all Sciaenidae) from Kedonganan fish market, South Bali coast, in November 2016, were infected with Pseudempleurosoma haywardi sp. nov. Prevalences in the first two croakers were 63% and 46%, respectively, and the two J. amblycephalus harboured three and five individuals. All three croakers represent new hosts for this monogenean genus. We provide infection rates, light microscopical observations, 3D confocal microscopical illustrations, and a morphometric comparison with all congeners. The new species differs in body size, the position and shape of the ovary and testes, and especially in the composition of the dorsal anchor complex, with the dorsal bar being anteriorly concave rather than planar or convex as in its congeners. The dorsal and ventral anchors of this new species are the longest in the genus, whereas the male copulatory organ is the smallest. The first DNA sequences for a member of this genus demonstrate the greatest similarity with endoparasitic freshwater monogeneans from African cichlid fishes. This suggests a freshwater origin for these marine endoparasitic monogeneans.

Species of Tetrancistrum Goto & Kikuchi, 1917 (Monogenea: Dactylogyridae) from the gills of the whitespotted rabbitfish, Siganus canaliculatus (Park) (Perciformes: Siganidae) off Omani coasts, with a description of Tetrancistrum labyrinthus n. sp.

Tetrancistrum labyrinthus n. sp. is described from the gills of the marine herbivorous fish Siganus canaliculatus (Park) found in the Western Indian Ocean (Sea of Oman and Arabian Sea). Comparative morphological analyses of all previously described species of Tetrancistrum Goto & Kikuchi, 1917 confirmed the distinct status of T. labyrinthus n. sp. The new species closely resembles T. suezicum Paperna, 1972 and T. oraminii Young, 1967 in the morphology of the male copulatory organ. However, it can be distinguished by possessing a thin handle-like anterior basal flange and a compound accessory piece that is composed of a tapering rod-shaped anterior part and a large cylindrical, elongated posterior part. The new species can be further distinguished from other Tetrancistrum species by its highly sclerotised and complex disc-shaped vaginal vestibule. This is the first record of Tetrancistrum from the Sea of Oman and Arabian Sea, and the fourth of nominal species of Tetrancistrum known to parasitise Siganus canaliculatus (Park). In addition, T. indicum Paperna, 1972 is re-described here with an updated locality record.

Morphological, ultrastructural, and molecular description of Unicapsula fatimae n. sp. (Myxosporea: Trilosporidae) of whitespotted rabbitfish (Siganus canaliculatus) in Omani waters.

Investigations regarding the parasite fauna of wild whitespotted rabbitfish (Siganus canaliculatus) Park, 1797 revealed white, spherical, loosely attached cysts measuring 896 (375-1406) µm in diameter in the inner endothelial wall of the esophagus and stomach. Mature spores inside these cysts corresponded to the original description of spores belonging to the genus Unicapsula Davis, 1924. Unicapsula fatimae n. sp. spores were 6.23 (5.60-6.60) µm in length and 6.80 (6.12-7.39) µm in width. The length of large polar capsule was 2.62 (2.18-2.97) µm and width was 2.65 (2.32-2.90) µm, and the extended large polar capsule filament length was 15.50 (11.71-19.99) µm. Transmission electron microscope images of the plasmodia revealed a complex cyst structure that was unique among other Unicapsula spp. Ultrastructural details of the host-parasite interface and developmental stages of a species from the Unicapsula genus are described for the first time. Histology of an infected esophagus revealed some abnormalities and changes in the host tissue around the infection site, including hypertrophy of host esophagus epithelial cells and hyperplasia of host glandular tubules. The parasite presented here has been added to the genus Unicapsula using comparative morphological analysis and ultrastructural investigations supported by 18S small subunit ribosomal DNA molecular analysis.

Omanicotyle heterospina n. gen. et n. comb. (Monogenea: Microcotylidae) from the gills of Argyrops spinifer (Forsskål) (Teleostei: Sparidae) from the Sea of Oman.

BACKGROUND: The Sultanate of Oman's aquaculture industry is expanding with an on-going assessment of potential new fish species for culture. The king soldier bream, Argyrops spinifer (Forsskål) (Sparidae), is one such species that is under consideration. During a routine health assessment of specimens caught in the Sea of Oman throughout the period November 2009 to March 2011, a number of gill polyopisthocotylean monogeneans were recovered. METHODS: A subsequent study of the monogeneans using a range of morphology-based approaches indicated that these were Bivagina heterospina Mamaev et Parukhin, 1974. In the absence of pre-existing molecular data, an expanded description of this species is provided, including a differential diagnosis with other species and genera belonging to the subfamily Microcotylinae Monticelli, 1892 with the subsequent movement of this species to a new genus to accommodate it. RESULTS: The polyopisthocotyleans collected from the gills of A. spinifer appear to be unique within the family Microcotylidae Taschenberg, 1879 in that, morphologically, they possess a pair of large, muscular vaginae each armed with a full crown of 16-18 robust spines and a unique dorsal region of folded tegument, which permits their discrimination from species of Bivagina Yamaguti, 1963. Sequencing of the SSU rDNA (complete 1968 bp) and LSU rDNA (partial 949 bp) places the specimens collected during this study within the subfamily Microcotylinae, but the LSU rDNA sequence differs from Bivagina and also from other microcotylid genera. Morphological features of B. heterospina sensu Mamaev et Parukhin, 1974 and the specimens collected from the current study are consistent with one another and represent a single species. The vaginal armature of these worms is unique and differs from all other genera within the Microcotylinae, including Bivagina, and its movement to Omanicotyle n. gen. to accommodate this species is proposed. CONCLUSIONS: A new genus, Omanicotyle n. gen., is erected to accommodate Omanicotyle [Bivagina] heterospina n. comb. which represents the first monogenean to be described from Omani marine waters. Given the pathogenic potential of microcotylids on captive held fish stocks, a full assessment of Omanicotyle heterospina n. gen. et n. comb. is now required before large-scale production commences.