Cancer spares no one: First record of neoplasm in parasitic barnacles (Arthropoda: Rhizocephala).

Cancer-like neoplasms are extremely rarely present in arthropods, particularly in crustaceans. Thus, it is assumed that these animals have some efficient cancer-preventing mechanisms. However, several cases of cancer-like neoplasms are described in crustaceans, though only for the Decapoda. We identified a tumor in the parasitic barnacle Peltogaster paguri (Cirripedia: Rhizocephala), and described its histological structure. A spherical cell mass consisting mostly of roundish cells with big translucent nuclei, prominent nucleoli, and sparse chromatin, and of cells with condensed chromosomes, was found in the main trunk of the P. paguri rootlet system. Numerous mitoses were observed in this area. Such tissue organization is utterly uncharacteristic of the Rhizocephala. Based on acquired histological data, we assume that this tumor is a cancer-like neoplasm. This is the first report of a tumor identified in the rhizocephalans, as well as in non-decapod crustaceans as a whole.

Histological description of Cercaria etgesii Shchenkov, 2017 daughter sporocysts (Trematoda: Pleurogenidae): compartmentalization of the brood cavity and germinal mass morphology.

Morphology of the daughter sporocysts of Cercaria etgesii Shchenkov, 2017 (Pleurogenidae) has been described according to conventional histological techniques and subsequent 3D reconstruction with Bitplanelmaris® software. Novel data were obtained concerning the spatial organization of the brood cavity of Pleurogenidae daughter sporocysts. It was shown that the laminated structures of the endocyst are lining the brood cavity and carry out its compartmentalisation by formation of the chambers around developing and disintegrating embryos of cercariae. First description of the germinal mass of the Pleurogenidae daughter sporocysts is given. No mitoses in germinal mass were evident although apparent production of the cercariae embryos by the sporocysts take place. The analogous principle of daughter sporocysts morphofunctional organisation was noted for the studied representatives of closely related taxa of trematodes: Pleurogenidae (C. etgesii) and Microphallidae (Microphallus 'pygmaeus' group).