Surface Topography of Hymenolepis diminuta by Scanning Electron Microscopy

Abstract

Scanning electron microscopy (SEM) of surface of Hymenolepis diminuta, particularly scolex, indicates that dense populations of microtriches occur on rostellum, suckers, and scolex proper. Average microtrichoid densities of 49.2/,U2, 64.8/,U2, and 56.4/j42 were obtained for these areas. Differences in size were not observed. The excellent preservation of microtriches attests quality of critical point drying method for preparing cestodes for study by high magnification SEM. Fine structural studies of tegument of cestodes have demonstrated that surface cytoplasm is extended as microtriches, consisting of cylindrical cytoplasmic bases capped by dense structures termed shafts (Read, 1955; Rothman, 1963; Jha and Smyth, 1969). Functionally, these microtriches have been suggested to: (1) increase surface area for absorption and secretion; (2) aid in maintaining position in host; and (3) agitate microhabitat (review by Lee, 1966, 1972; Smyth, 1969, 1972). Such functions are in part supported by observations which suggest that density of microtriches changes throughout strobila (Rothman, 1963; Berger and Mettrick, 1971). Although Rothman (1963) reported that in Hymenolepis diminuta the apical region of scolex is devoid of microtriches or has very fine ones several authors have reported their presence on scolex of other cestodes: Echinococcus granulosus (Jha and Smyth, 1971), E. multilocularis (Sakamoto and Sugimura, 1969, 1970), Diphyllobothrium erinacei (Yamane, 1968), Taenia hydatigena (Featherston, 1971), sparganum of Spirometra erinacei (Kwa, 1972), and Hymenolepis nana (Rosario, 1962). Berger and Mettrick (1971) reported polymorphism in microtriches from Hymenolepis diminuta, H. microstoma, and H. nana by SEM. They suggested that microtriches played a role in locomotion of these organisms within host's gut. The only other SEM of H. diminuta described surface topography of eggshell (Voge, 1969). The present study was undertaken in an attempt to determine by scanning electron Received for publication 5 January 1973. microscopy if such microtriches were present on apical region and suckers of H. diminuta and if variation in size of these microtriches, as reported by Berger and Mettrick (1971), could be confirmed. MATERIALS AND METHODS The Rice Institute strain of Hymenolepis diminuta was maintained in laboratory in Holtzman rats. Adult worms were collected from experimentally infected rats. Specimens were fixed in cold 4% paraformaldehyde (Lynn et al., 1966) in 0.1 MN oacodylate buffer for 2 hr, and subsequently sonicated to remove intestinal debris. Tissues were rapidly dehydrated in an ascending series of ethanol solutions, transferred through a series of intermediate fluids (3:1, 2:1, 1:1) of 100% ethanol and amyl acetate to 100% amyl acetate according to procedures of Anderson (1951, 1966). Specimens were transferred to liquid CO2 in a Denton DCP-1 critical point dryer until amyl acetate was removed. The temperature was elevated to above critical point of CO, (31 C, pressure 72.9 atm) and bled off. The dried specimens were positioned on metal specimen stubs, outgassed in a vacuum evaporator, rotarycoated with gold palladium (200 A or less), and examined with an AMR 1000 scanning electron microscope. Values obtained for microtrichoid density were determined by counting microtriches from 1-/u2 areas chosen in a random manner. Values represent minimum values as all microtriches may not be visualized in micrographs. Diameter values were determined by measuring diameters of 25 randomly chosen microtriches. Stated values represent average followed by range in parentheses.