The ultrastructure of helminth. 4. Cercaria of Schistosoma japonicum.

The body wall of the cercaria of Schistosoma japonicum is covered with a thin integument which is connected to epithel cells located under the uscle layer. On the outer and the basal surfaces of the integument are seen thin limiting membranes. In the matrix of the integument are distributed numerous dense granules, vacuoles and spines. The rootlet of the spine is attached to the basement membrane of the integument. The circular and longitudinal muscle layers, both underlying the integument, have smooth muscle fibers composed of thick and thin myofilaments. The cercaria possesses five pairs of secretion gland cells which are divided into two groups of three anterior and two posterior pairs. Both gland cells are filled with secretion balls. The tail of cercaria is likewise covered with a thin integumen t, whose structure is identically the same as the body integument. Beneath the integument are located thin circular and longitudinal muscle layers. The circular muscle cells have smooth muscle fibers, but the longitudinal muscle cells have striated muscle fibers. These muscle cells contain many large mitochondria. On observing the cross-sections of the tail at the flame cell level the arrangement of these muscle can be divided into four muscle groups and each muscle group reveals four or five muscle cells. The excretory system is well developed and has flame cells, excretory canal and bladder. ∗PMID: 4247893 [PubMed indexed for MEDLINE] Copyright c ©OKAYAMA UNIVERSITY MEDICAL SCHOOL Acta Med. Okayama 24, 205-224 (1970) THE ULTRASTRUCTURE OF HELMINTH 4) CERCARIA OF SCHISTOSOMA JAPONICUM Seiiti INATOMI, Yasumasa TONGU, Daigoro SAKUMOTO, Setsuo SUGURI and Kazuo ITANO Department of Parasitology, Okayama University Medical School, Okayama, Japan (Director: Prof. S. Inatomi) Received for publication, December 25, 1969 In recent years a number of papers dealing with the ultrastructure of cercariae of Trematodes have been published. Especialy, the reports of KRUIDENIA & VATTER (1958), INATOMI (1960) and LUMSDEN & FOOR (1968) have respectively reported in some details the fine structure of the cercaria of Schistosoma. This study was undertaken to elucidate the fine structures of the cercaria of Schistosoma japonicum. MATERIALS AND METHODS The cercaria collected for the study were those that naturally escaped from infected snail host, Oncomelania nosophora (Kurume strain). The cercaria were immediately fixed in I % cold glutaraldehyde solution buffered with phosphate (pH 7.4) for 30 minutes, then washed with phosphate buffer. These were again subjected to the post-fixation with cold 2 % osmium tetroxide solution in phosphate buffer (pH 7.4) for two hours, dehydrated with ethanol series by routine methods immediately after the fixation and embedded in methacrylate or Epon 812. Specimens with these materials were cut with Porter-Blum ultramicrotome, and thin sections were stained with uranyl acetate and lead nitrate. For the observations the electron microscopes of Hitachi HS-6, HS.8, HU-ll, and that of Nihondenshi JEM-7 type were used. RESULTS Integument: The body and tail of cercaria are covered with thin integuments from about 0.1 to 0.5 p. thick, and the integument is con· nected with epithelial cells located under the muscle layer, forming a large syncytium structure identical with that of the adult worm. On both outer and basal surfaces of the integument is seen a limiting membrane of about 80 A in thickness. In integument matrix are distributed numerous discoidal or rod-shaped dense granules of varying sizes, vacuoles, and minute spines of about 0.1 p. or more in diameter and about 3 to 4 /1. in 205 1 Inatomi et al.: The ultrastructure of helminth. 4. Cercaria of Schistosoma Produced by The Berkeley Electronic Press, 1970 206 S.INATOMI, Y. TONGU, D. SAKUMOTO, S. SUGURI & K.ITANO length. As to the structure of these spines, it presents a crystalloid structure congregated of high dense fine granules that measure about 80 A in diameter and these granules run transversely and longitudinally to the long axis of the spine, forming a lattice structure. The rootlet of such spines reaches the basement membrane of the integument, and the part extending from the integument surface is covered with a thin plasma membrane which covers the surface of the integument itself. The irregular projections of the integument are observed on the body surface, especially, many irregular finger-like projections are distributed at the head part of cercaria. The basement membrane of the integument is often observed invaginating into the matrix. The mitochondria observable in the integument have relatively simple, small and clear cristae. The fiber layer is of varying thickness, as connective tissue is situated between the integument and the muscle layer. This layer is constructed of the fine net-work with very fine fiber that is about 60 Ain diameter. Body muscle: The muscle layer consisted of the outer circular and inner longitudinal muscle layers is located under the fiber layer. The fibers of these muscle cells are nonstriated but are not really smooth muscle. The myofibrils are constructed of both thick and thin myofilaments. And also, A and I bands, Z-discs are not observable on the myofibrils. However, the dense bodies are scattered occasionally on the myofibrils. The diameter of thick myofilaments is 250 A and that of the thin ones 50 A. The thick myofilament is surrounded hexagonally with about 12 thin myofilaments. The agranular endoplasmic reticula are distributed along the myofibil close to the sarcolemma. Almost all the mitochondria of muscle cells, numberless glycogen particles and the nucleus are located along the periphery of the myofibril. Tail muscle: The muscle of the tail is constructed of an outer thin circular layer and an inner longitudinal muscle layer. The longitudinal muscle cell has striated myofilaments which are classified as thick and thin filaments. These myofilaments form different arrangements at A and I bands. The striations which are expresented by dense Z-discs observed in these cells reflect a regular transverse arrangement associated with the thin myofilaments. Such a striated muscle cell is very long, being as long as about 60 r~, and runs top to tip of the tail. The arrangement of muscle cells at the cross-section of the flame cell level of the tail can be divided into 4 muscle groups and each muscle group comprises 4 or 5 muscle cells. These muscle cells run diagonally, as they approach the end gf the tail! the cell number gradually decreases. These muscle cells contain 2 Acta Medica Okayama, Vol. 24 [1970], Iss. 2, Art. 7 http://escholarship.lib.okayama-u.ac.jp/amo/vol24/iss2/7 The Ultrastructure of Helminth 207 many large mitochondria, sarcoplasmic reticula and glycogen particles between the myofilaments. Epithel cell: The epithel cells are located in a deep portion of the body wall and connected to each other. These cells containing numerous annulated lamellar dense secretion granules of varying sizes, glycogen particles, endoplasmic reticula with ribosome granules, Golgi complex, mitochondria and nuclei, are connected to the integument by protoplasmic tubules. They are not so well developed and are not so numerous as in the case of adult worm. Excretory system: The excretory system is well developed and has the flame cells, the excretory canal as its primitive nephron, and the excretory bladder. The flame cell measures about 14 to 15,11. in length, 3 to 5 p. in width, and at its tip it has a large nucleus with relatively small cytoplasm and several mitochondria around the nucleus. From this cytoplasm nearly 100 long cilia of about 0.1 /1. in diameter are growing and running towards the excretory canal in a brush.like form. These cilia show typical cilium pattern. At the junction of the excretory canal and the cytoplasm there is observed a slit of filter part of funnel.like shape and the thickness of this part is about 0.2 ,IL. Sense organ: A certain number of sensory hairs as terminal sense organ are observed on the integument. The sensory hair is constructed of two parts consisting of the cilia and bulb.like portion. The bulb and root of cilia are surrounded by the integument. The diameter of the bulb varies from 0.6 to 1 ,u. The diameter of the cilia is 0.23 fJ.. The rootlet of the cilia reaches into the central part of the bulb. An open space of the inside of the bulb is filled with numerous small vesicles and mitochondria, and several microtubules are situated inside the bulb. The desmosomes are observed between the bulb and the integument surrounding the bulb itself. Two electron dense concentric rings associated with the micro. tubuIes are connected with the root of the cilia. Secretion gland: In the posterior half of the body of cercaria, there are observed five pairs of penetration glands. They are classified into two groups by the morphology of secretion granules, and each penetration gland cell is filled with secretion granules. Three anterior pairs of these gland cells have rather dense secretion balls of varying sizes measuring about 0.05 ll. in diameter. The two posterior pairs of gland cells have low dense secretion balls with numerous round vacuoles of about O. I ll. in diameter. Many microtubules run along the inside of these gland cell membrane. The flattened nucleus which is compressed by producing the secretion granules themselves, is often found on the secretion gland cell 3 Inatomi et al.: The ultrastructure of helminth. 4. Cercaria of Schistosoma Produced by The Berkeley Electronic Press, 1970 208 S.INATOMJ, Y. TONGu, D. SAKUMOTO, S. SUGURJ & K.ITANo membrane. Digestive organ: The digestive canal is of a very simple and not well. developed structure. The inner surface of the esophagus is covered with a thin integumental layer of about 0.1 p. in thickness. There can be seen several plait-like projections of the integumental layer at the inner surface of the esophageal and intestinal lumen, but not any real microvilli. The digestive canal is surrounded by small muscle groups. Fig. 1 The body wall of the cercaria of Schisto:oma japonicum. There are numerous rods>aped or round dense secretion granules, and minute spines in the matrix of the integument covering the body surface. The muscle layer underlying the fibrous layer as connective tissue is consisted of two layers of circular and lO:1gitudinal muscles having smooth muscle fibers. The epithel cell contains numerous secretio:1 granules. 4 Acta Medica Okayama, Vol. 24 [1970], Iss. 2, Art. 7 http://escholarship.lib.okayama-u.ac.jp/amo/vol24/iss2/7 The Ultrastructure of Helminth