December 2007 - The Indian Society for Parasitology

SEM studies on a few didymozoids121scales of S. obtusata. Fresh specimens were collected surfaces of two individuals and with their respectivefrom S. obtusata and S. jello. The parasites were central portion in contact at right angles, securelyprocessed for SEM studies following the procedure interlocked by folds of the body arranged in a radiatingdescribed by Veerakumari and Munuswamy (1999). manner in the central region of the disc (Fig. 15–18).The worms were washed with phosphate-buffered The folds on the edges further strengthen the contact.saline (pH 7.2) several times to free them from mucus The periphery of the anterior and posterior region ofand then fixed in 4 % glutaraldehyde (pH 7.2) over the ventral surface is both thin and smooth. The forenightat 4°C. The worms were washed several times body arises from the center of the ventral surface,again in cold 0.1M phosphate buffer. The worms were which is slender at its base and globular at its tip (Fig.post-fixed in 1% osmium tetroxide prepared in 0.1M 19). The periphery of the dorsal surface is rough withphosphate buffer for 4 h at 4°C. They were furrows, spines, pits and papillae. Most of the papillaesubsequently washed in distilled water and then are dome shaped, few are pitted and very few aredehydrated in graded alcohol series. After this uniciliated (Fig. 20). Pectinate spines are common atprocess, the specimens were transferred to 100 % the edge of the anterior region of the parasite (Fig. 21).acetone for one h, dried and the worms were glued onmetal standard stubs, coated with gold in vacuum andDISCUSSIONexamined by using a SEM Hitachi 3415A. The diversification and modification in thePhotomicrographs were taken at various integumental structures of digenetic trematodes canmagnifications with an Exacta Exa 1 camera, using be considered as parasitic adaptations to individualIlford Fp4 type film.microhabitats (Abidi et al., 1988). The integument ofRESULTStrematodes is generally considered as a protectivesheath. Morris and Threadgold (1968) reported thatPertinent features of the integumental surfaces of the integument aids in absorption. Integument alsoadult A. operculare, D.singularis and P. polyaster as plays a vital role in secretion, excretion (Silk et al.,observed by SEM are depicted in Fig. 1–21.1969) and osmoregulation (Sneft et al., 1961). Thetegument of trematode thus plays important role inIn A. operculare, the body is divisible into fore andvarious physiological functions; however, onlyhind-body and the ventral surface of the tegument isincidental attention has been given to the architecturerough (Fig. 1). The ventral surface of the fore-bodyof the integument of didymozoids.possesses conical shaped projection (Fig. 2). The hindbody shows ridges and folds which are arranged like a The present investigation clearly reveals that there isnetwork giving a honeycomb appearance (Fig. 3 and diversification with reference to surface topography4). The dorsal surface is rough with pits and sensory of didymozoids. These variations may be due topapillae (Fig. 5). The eggshells are oval in shape with various measures including adaptations of the parasitean operculum. The egg shells measure 6.4 × 4µ (Fig. to microenvironment as the niche of each parasite6). differs. This is supplemented by the findings of Abidiet al. (1988), who observed difference in tegumentIn D. singularis, the dorsal and dorso-lateral surfacesstructures of various digeneans occupying variousare characterized by tubercles, folds, pits and spinesniches and suggested that it is a parasitic adaptation.(Fig. 7–10). The tubercles are numerous on the middorsalsurface. The tegumental spines appear as The tegumental folding, ridges, furrows and lamellarpointed structures (Fig. 10), lack dentition and are network impart considerable stretching capability tomainly distributed on the lateral and dorsal surfaces. the didymozoids. These structures also increase theDome shaped sensory papillae and microvilli like surface area for absorption of micro molecularprojections are observed on the ventral surface (Fig. nutrients (Abidi et al., 1988). The ridges on the11 and 12). Genital aperture is present on the ventral integument are either due to longitudinal anteriorsurface (Fig. 13). Towards the periphery, the constriction (Bakke and Lien, 1978) or due to internalmicrovilli are arranged irregularly on the annulated musculature (Nollen and Nadakavukaren, 1974).surface and cobblestone like projections are alsopresent (Fig. 14).Similar tegumental folding, ridges and furrowsobserved in all the species of didymozoids in theP. polyaster occur always in pairs underneath the present study on the dorsal and dorso-lateral surfacesscales of S. obtusata, pressed between the ventral suggest that surface structures may perform the same