[Ultrastructural studies on the surface of Paragonimus westermani metacercaria]

The present study was undertaken to demonstrate the surface structure of Paragonimus westermani metacercaria in Korea with special reference to the distribution of sensory papillae. Metacercariae were isolated from crayfish, one of the second intermediate host of P. westermani in Bogil island, Chollanam-do (Province), Korea, where has been known as an endemic area of human paragonimiasis. Isolated metacercariae were excysted and examined with light, scanning and transmission electron microscopes for morphological features. On the surface of metacercariae, three types of sensory papillae were identified. Large domed papillae (3-5 micrometer), which were covered with wrinkled plasma membrane of the worm, were distributed on the oral and ventral suckers only. On the oral sucker, these large domed papillae were 12-13 in number. On the other hand large domed papillae on the ventral sucker were constantly 6 in number and hexagonal in distribution. Small domed papillae (2-3 micrometer), of which surface was more smooth than those of large ones, were distributed symmetrically on the ventral (30-32 pairs) and dorsal surfaces (40-42 pairs). Ciliated papillae (0.8-1.5 micrometer) were observed about 5-6 in number around the oral sucker and 3-5 pairs each on the ventral and dorsal surface of the body. Single pointed spines covered the entire surface of the body except around the excretory pore. Spines on the anterior part of the body were 0.9-2.0 micrometer in length and 45-55/100 square micrometer in number, and were gradually reduced in length (0.4-1.4 micrometer) and in number (12-27/100 square micrometer) toward the posterior part. The body wall of P. westermani metacercariae was consisted with anucleated syncytium layer, fibrous interstitial layer and musclar layer. In the anucleated syncytium, biconcave (0.15-0.55 micrometer) and spherical (0.08-0.16 micrometer) secretory granules, which were transferred from epidermal cells via protoplasmic tubules, mitochondria and ribosomes, were observed. Spines originated around the basement membrane protruded externally. Epidermal cells were consisted with a nucleus and a cytoplasm, and connected to syncytium with protoplasmic tubules. In the cytoplasm many secretory granules, mitochondria, Golgi complex, endoplasmic reticula, ribosomes and lipid droplets were observed.