Organization of Lacunar and Muscular Systems of <i>Polyascus polygeneus</i> and <i>Parasacculina pilosella</i> (Rhizocephala: Polyascidae)

Circulatory systems are characteristic of most multicellular animals. In parasitic organisms, which may differ strikingly from their free-living relatives, such systems remain the least studied. Rhizocephala (Pancrustacea: Cirripedia) are among the morphologically most derived parasitic crustaceans. In the adult rhizocephalan female, transport presumably takes place along the lacunar system inside the interna rootlets and the externa. The aim of our study was to visualize and describe the lacunar and muscular systems in the externa of Polyascus polygeneus and Parasacculina pilosella (fam. Polyascidae) using micro-computed tomography and confocal microscopy. The lacunar system in the externae of both species consists of the stalk lumen, mesentery lacuna accompanying the visceral mass and mantle lacunae. These elements of the lacunar system are similar to those previously described in Peltogasterella gracilis (fam. Peltogasterellidae). However, the interposition of these elements differs. The organization of the muscular system mostly corresponds to previous descriptions in other rhizocephalan species, however some unexpected results were obtained. For example, P. polygeneus has an age-related differentiation of mantle musculature, which was not described before for any rhizocephalan species. Obtained data on lacunar and muscular systems organization allow us to assume the change in the externa body axes in the family Polyascidae.