A New Host and a New Locality for Aspidogaster limacoides Diesing, 1834 (Trematoda: Aspidogastridae) Infecting the Caspian Freshwater Turtle Mauremys caspica (Gmelin, 1774) in Basrah Province, Iraq

A total of 21 specimens of Aspidogaster limacoides Diesing, 1834 were detected from the small intestine of eight infected specimens of the Caspian freshwater turtle Mauremys caspica (Gmelin, 1774) captured from Al-Mashab River, northwest Basrah City. As the present parasite represents its first record in the turtle as a new host and in Basrah city as a new locality, a redescription, measurements and illustration are presented.

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.

Presence of Bucephalus polymorphus, Echinoparyphium recurvatum and Aspidogaster limacoides (Platodes, Trematoda) in the visceral mass of Dreissena polymorpha (Mollusca, Bivalvia)

The invasive bivalve species Dreissena polymorpha (Pallas, 1771) has become one of the most dominant spe-cies in many lakes and rivers of Europe and North Ame-rica. The aim of this study was to investigate changes in the structure of the visceral mass depending on the repro-ductive cycle and to determine the presence and effects of trematodes on the zebra mussel. Mussels were collected from the Dubrava dam reservoir during eight sampling sessions from January to December 2000. For histological analysis, 80 mussels were placed in Bouin’s fixative for 24 hours, embedded in paraffin and cut with a microtome into 10 μm slices. The sections were then stained with haema-toxylin and eosin. Analysis of non-infected bivalves indi-cated that gametogenesis started in late summer, while spawning began in April. In July, the majority of mussels were in the post-spawning stage. Two mussels were in-fected with Bucephalus polymorphus, one with Echi-noparyphium recurvatum and one with Aspidogaster lima-coides. Obtained results demonstrated that the gonads were the most affected organs in mussels infected by B. poly-morphus, the infection by A. limacoides resulted in a sig-nificant reduction of all investigated organs, while the infection by E. recurvatum had no visible pathogenic changes in the structure of visceral mass.

Advanced stages of embryonic development and cotylocidial morphogenesis in the intrauterine eggs of Aspidogaster limacoides Diesing, 1835 (Aspidogastrea), with comments on their phylogenetic implications

Ultrastructural aspects of the advanced embryonic development and cotylocidial morphogenesis of the aspidogastrean Aspidogaster limacoides are described. The posterior or distal regions of the uterus are filled with eggs containing larvae at advanced stages of morphogenesis and fully-formed cotylocidia. Various stages and organs of this larva are described in detail, including the aspects of the developing and fully-differentiated cotylocidium, the body wall (tegument and musculature), glandular regions and the protonephridial excretory system. Blastomere multiplication by means of mitotic divisions takes place simultaneously with the degeneration or apoptosis of some micromeres; this frequently observed characteristic is compared and discussed in relation to corresponding reports for other neodermatans. During the advanced stages of the embryonic development of A. limacoides, the vitelline syncytium disappears and the size of the embryo increases rapidly. Evident polarization of the differentiating larva was observed; towards one pole of the egg, cytodifferentiation of the mouth, surrounded by the oral sucker and cephalic glands, takes place, whereas, towards the opposite pole, differentiation of the posterior sucker (incipient ventral disc) occurs. The oral and posterior suckers are formed from numerous embryonic cells which have differentiated into myocytes. The central part of the oral sucker undergoes invagination and forms the future pharynx and intestine. Fully-developed cotylocidia of A. limacoides have a neodermatan type of tegument, flame cells and two types of glandular structures. These results suggest a sister relationship between the Aspidogastrea and the Digenea, although the systematic position of aspidogastreans in relation to other platyhelminth taxa remains somewhat equivocal.