SEM and TEM study of the armed male terminal genitalia of the tapeworm Paraechinophallus japonicus (Cestoda: Bothriocephalidea).

For the first time, the ultrastructure of the armed cirrus of an echinophallid cestode, Paraechinophallus japonicus (Yamaguti, 1934), has been studied with the use of scanning and transmission electron microscopy. Two sets of eversible copulatory organs (approximately 300 microm in length and approximately 130 microm in width) are present on the dorsal side of each segment near the lateral margin of the strobila. Except for the terminal portion, the cirrus is covered with large spines (up to 40 mircom long, measured from SEM photomicrographs) composed of 2 parts. The basal portion contains a lobed electron-dense outer region that gives way to a reticular meshwork of electron-dense material. The apical region of the spines, composed of a homogeneous, moderately electron-dense matrix, is slightly curved distally. Spines are covered with a cortical zone. Between the spines, the distal cytoplasm is covered with microvilli of about 1.2 microm in length. The wall of the cirrus sac, which is approximately 500 microm long and approximately 250 microm wide, is composed of 2 layers of muscles, i.e., an internal layer of circular muscles and external longitudinal muscles. Microvilli on the cirrus of P. japonicus are reported for the first time in the Cestoda, whereas the spines on the cirrus may represent a synapomorphy of bothriocephalidean cestodes of the Echinophallidae.