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A Contribution to the Life History of Bucephalus longicornutus (Manter, 1954)

Discussion of Adult

Discussion of Adult

Compared with the metacercaria, adult B. longicornutus have tentacles surmounting the anterior sucker and show considerable development of the reproductive system. The development of elements of the latter in the hindbody has a considerable bearing on the position of the mouth and intestine, a feature which differs considerably between metacercaria and adult. Remaining differences are relatively minor. Spines are absent from the cuticle overlying the band of radial muscles of the adult sucker; and the flap of cuticle closing off the open end of the sucker musculature in the metacercaria, while still present in the adult, is not conspicuous. Both of these differences may possibly result from the effects of attachment to the intestinal wall of the definitive host.

Only three immature worms were recovered from the material examined. Two of these had their tentacles partially extended and all three, apart from the absence of eggs, were very similar to sexually mature adults.

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Manter (1954) placed the above species in the genus Alcicornis McCallum, 1917. The single specimen he recovered from one of four Kathetostoma giganteum from Cook Strait was mounted in lateral view and the sucker-like nature of the anterior end was not evident, appearing instead rhynchus-like, and this is diagnostic of the genus Alcicornis. Manter compared the species with other known species of Alcicornis. However, because of the change in generic status proposed here it is now necessary to compare Bucephalus longicornutus with related species of Bucephalus.

In the possession of one thorn-like process at the base of the tentacle, B. longicornutus resembles B. polymorphus von Baer, 1827, B. introversus Manter, 1940, and B. scorpaenae Manter, 1940. However, it differs from B. polymorphus in that the cirrus sac is much longer in relation to the total length, the tentacles do not taper to a point and the thorn-like process on the tentacle is situated nearer the base of the tentacle; from B. introversus in that the anterior sucker does not introvert into the anterior end of the body and the structure of the genital atrium is not as complex; and from B. scorpaenae in that the excretory vesicle is shorter, the pars prostatica is not subdivided and the genital lobe is simpler in structure.

B. longicornutus does show some resemblance to B. kathetostomae (Manter, 1934) (a species in which the structure of the tentacles is unknown), from a related host, Kathetostoma albigutta Bean. However, it differs from B. kathetostomae in the absence of the muscular sphincter surrounding the genital pore, shorter genital atrium, the absence of processes on the eggs and considerably shorter excretory vesicle.

There are two main differences between Manter's description of B. longicornutus and that given above. These are the bipartite rather than ovoid seminal vesicle, and the longer tentacles. Both of these characters are considered to be subject to variation. The shape of the seminal vesicle is probably dependent on the amount of sperm present and the length of the tentacles on their degree of contraction.

The variations noted for B. longicornutus are considerable. The position of the internal organs is apt to be governed by the degree of contraction of the body on fixation and by the number of eggs in the uterus. The arrangement of the vitelline follicles, which has been mentioned above, illustrates this latter point. Egg size is extremely variable between specimens from different hosts but is generally more or less constant within a group of specimens from the same host. A similar phenomenon has been noted by Manter (1940a) for B. varicus Manter, 1940 (synonym: B. polymorphus of Nagaty, 1937). Slight variations of from 0.002 to 0.004 exist between egg sizes in a given specimen as was also noted by Manter (1954) in the one specimen of B. longicornutus which he examined. Egg size cannot be correlated with the length of the specimen, e.g., a specimen of 1.718 long had eggs 0.021 by 0.016 while a specimen 1.818 long had eggs 0.032 by 0.020; but can, however, be correlated with the number of eggs present, e.g., a specimen 1.110 long had few eggs and these were large, being 0.035 by 0.022 while a specimen 1.496 long had many eggs and these were relatively small, being 0.024 by 0.016.

B. longicornutus parallels B. varicus in the range of variation exhibited. Such a range has not been noted for other species of the genus. However, many of these species are either insufficiently described (vide van Beneden, 1870) or known only from a few specimens (vide Velasquez, 1959). Characters such as total length, relative position of internal organs and minor differences of only 2μ to 3μ in egg size have, in some cases, been used to separate species (vide Velasquez, 1959). In view of the variations of these characters known for B. varicus and B. longicornutus, two species which have been collected from a number of different host species and the same host species respectively, these specific distinctions should be regarded as tentative and possibly subject to alteration after reference to further material.

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The most constant features noted in those specimens of B. longicornutus examined were the nature of the genital atrium and genital lobe, and the floor of the anterior sucker. Unfortunately, descriptions of these features are absent from many systematic papers dealing with species of Bucephalus and they may, in future, prove more satisfactory criteria for differentiating between species than those used in the past.