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<br />VOL. 102, NO, 3, JULY 1983
<br />
<br />241
<br />
<br />;.
<br />
<br />features of B. acheilogna,thi (Molnar & Murai, 1973; Yamaguti, 1934; Yeh,
<br />1955), but the ultrastructure of this species has not been described.
<br />In the present study, both scanning electron microscopy (SEM) and trans-
<br />mission electron microscopy (TEM) were used to study the scolex and tegu-
<br />ment of immature, mature, and gravid forms of B, acheilognathi, Results are
<br />compared with similar observations made on other cestode species.
<br />
<br />MATERIALS AND METHODS
<br />
<br />Bothriocephalus acheilognathi (at least 10 specimens each of non-seg-
<br />mented, segmented, and gravid stages) were recovered from mosquitofish and
<br />rinsed in a 0.65% saline solution, fixed for 1, 2, or 12 h in 3% glutaraldehyde
<br />in 0.1 M sodium cacodylate buffer (pH 7.1), transferred to a buffer rinse, and
<br />dehydrated in an ascending series of ethanol solutions. Specimens were crit-
<br />ical-point dried, mounted on aluminum stubs with double-stick cellophane
<br />tape, sputter-coated with gold-palladium, and viewed with a Philips SEM
<br />501. Worms for TEM were fixed as above prior to secondary fixation in 1%
<br />osmium tetroxide and dehydration in an ascending series of ethanol solutions,
<br />The specimens were embedded in epoxy resin, seQtioned with a Sorvall MT-
<br />2B ultramicrotome, mounted, double-stained with uranyl acetate and lead
<br />citrate, and viewed with a Philips TEM 400.
<br />
<br />RESULTS
<br />
<br />6
<br />
<br />Scanning Electron Microscopy
<br />
<br />The anterior portion of Bothriocephalus acheilognathi, when viewed in
<br />the SEM, is composed of a heart-shaped scolex with two long, deep, pear-
<br />shaped bothria (Fig, 1), A bilobed apical disc also is present, although it is
<br />not a prominent feature (Fig. 2), The outer portion of the scolex tegument is
<br />uniformly and densely composed of a single morphologically distinct type of
<br />microthrix, Dome-shaped tumuli, approximately 1.35 ]Lm wide, also are nu-
<br />merous and uniformly spaced at a distance of 2.4-4,5 ]Lm on the scolex (Fig.
<br />3), No obvious differences were observed in microthrix or tumulus density
<br />among the scolices of gravid, segmented, or non-segmented worms; however,
<br />within the bothria on the scolices of all of these developmental stages, mi-
<br />crotriches are more slender in appearance. Moreover, tumuli (0,6-0.7 ]Lm) are
<br />less wide than on the outer surface of the scolex (Fig. 4). No other surface
<br />structures were observed in association with the tumuli.
<br />Posteriorly, tumuli are less numerous (5.2-13.2 ]Lm apart) on immature seg-
<br />ments (Fig. 5) and are entirely absent from mature and gravid proglottids.
<br />Sensory structures were not discernible on the surface of these proglottids
<br />using SEM, but they were evident in sections examined by TEM.
<br />
<br />Transmission Electron Microscopy
<br />
<br />Tumuli of the scolex contain dense-staining inclusions (Fig. 6). The basal
<br />lamina is evaginated and appears to form a duct through the tumulus, This
<br />duct also contains dense-staining inclusions. Scolex microtriches are rather
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