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<br />246
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<br />TRANS, AM, MICROSC, SOC,
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<br />DISCUSSION
<br />
<br />The fine structure of Bothriocephalus acheilognathi is similar in many
<br />respects to that of other pseudophyllidean tapeworms. The heart-shaped sco-
<br />lex, without a prominent apical disc, characterizes several species, including
<br />Eubothrium parvum (see Andersen, 1979), Diphyllobothrium dentriticum,
<br />D, latum, D. ditremum (see Andersen, 1975), and Bothriocephalus scorpii
<br />(see Jones, 1975). However, among the species of Bothriocephalus found in
<br />the United States, only B, acheilognathi has a heart-shaped scolex; the other
<br />six species have elongated scolices. As pointed out by Hoffman (1976, 1980),
<br />this characteristic is a diagnostic feature for B, acheilognathi in the United
<br />States.
<br />Dome-shaped tumuli are uniformly spaced on the surface of the scolex of
<br />B, acheilognathi, Tumuli were first described by Boyce (1976) who observed
<br />them on adult Eubothrium salvelini, Clestobothrium crassiceps, and Both-
<br />riocephalus scorpii, all pseudophyllidean tapeworms. Arme & Threadgold
<br />(1976) noted the presence of tumulus-like structures on Eubothrium crassum,
<br />also a pseudophyllidean of fish. Subsequently, Tedesco & Coggins (1980)
<br />corlducted a TEM study of the tegument of adult E. salvelini which revealed
<br />the presence of electron-dense inclusions within the tumuli. Their work in-
<br />dicated that the inclusions were manufactured by the endoplasmic reticulum,
<br />packaged by the Golgi apparatus within the perinuclear cytoplasm, and trans-
<br />ported via ducts to the surface. Although the present study did not follow the
<br />inclusions from synthesis through deposition in the tumuli, the observations
<br />that were made are consistent with those of Tedesco & Coggins (1980). Thus,
<br />the Golgi apparatus was active within the perinuclear cytoplasm, and the
<br />inclusions, apparently packaged by these organelles, were of similar size to
<br />the structure observed within the tumuli of E. salvelini. Other morphological
<br />features of tumuli on B, acheilognathi were consistent with the previous
<br />descriptions of tumuli on other species.
<br />Tumuli have been described previously only from adult pseudophyllideans
<br />recovered from fish hosts (Boyce, 1976; Tedesco & Coggins, 1980). The plero-
<br />cercoids of E, salvelini and Diphyllobothrium sp. do not possess tumuli, even
<br />though they are present on the tegument of adults of these species (Boyce,
<br />1976). By contrast, newly recruited immature B, acheilognathi, as well as
<br />mature and gravid specimens, possess tumuli. Previous studies did not ex-
<br />amine immature worms within the definitive host, and since B, acheilognathi
<br />does not have a plerocercoid stage (Freeman, 1973), any comparisons are
<br />difficult. However, tumuli must develop soon after the parasite reaches the
<br />definitive host since these structures appear on very young individuals of
<br />(four days old) B, acheilognathi,
<br />The distribution of tumuli varies greatly among scolex, immature, mature,
<br />and gravid segments of B, acheilognathi, the structures being most dense on
<br />the scolex, fewer in number on immature segments, and completely absent
<br />from mature and gravid proglottids, Boyce (1976) noted a similar pattern in
<br />the distribution of tumuli on the cestodes he studied, but Tedesco & Coggins
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