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A Contribution to the Life History of Bucephalus longicornutus (Manter, 1954)
Description
Description
A sporocyst is milky-white, elongate, rounded, hollow, branching, and swollen at irregular intervals as brood chambers which contain developmental stages of cercariae (Text-fig. 1, B, E, F, G). Brood chambers range from 120μ to 750μ. in diameter, and are up to 3.5cm long. Narrower regions separating brood chambers, 45μ. to 110μ in diameter by 20μ to 3.5cm long, may exhibit a beaded appearance.
Longest portion of a single sporocyst isolated, 6.1cm long, branched dichotomously at an average of every 2.2cm. Total length and branchings of a single sporocyst not determined, due to its fragility and complex inter-twinings with its own branches and the branches of other sporocysts. No early developmental stages of sporocysts were recovered from dissection of 44 oysters, and sectioning 8 oysters, all of which were not obviously infected with sporocysts.
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Text-fig. 1.—Bucephalus longicornutus. Morphology and anatomy of the sporocyst: Fig. A, T.S. of a sporocyst; Fig. B, whole mount of a portion of a sporocyst; Fig. C, T.S. of a brood chamber; Fig. D, portion of a T.S. through the sporocyst wall of a brood chamber; Fig. E, outline sketch of a branched portion of a sporocyst; Figs. F and G, variations in the morphology of the sporocyst. For abbreviations see p. 9.
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Right lateral view of a specimen of Ostrea lutaria Hutton, from Area B, Foveaux Strait, infected with the sporocysts of Bucephalus longicornutus (Manter, 1954). The visceral mass has been teased open to display the sporocyst tubules more clearly.
5μ to 6μ in diameter, usually with one distinct, eccentrically or centrally situated nucleolus and some peripheral chromatin; and ovoid nuclei, 3μ to 4μ in diameter, containing scattered chromatin granules which may resemble nucleoli, are considered as mesenchymal (somatic) nuclei. In narrower regions, larger of these nuclei lie, in general, nearer cuticle (Text-fig. 1, A). Both types are common throughout all regions of sporocyst; in representative cross section, between 28 and 38 mesenchymal nuclei are generally present. Germinal nuclei are found in syncytium of sporocysts from gill interribs, in and near terminal regions of sporocyst, usually numbering 1 to 2 per cross section. They are spherical, 5μ to 7μ in diameter, with a conspicuous, centrally situated nucleolus, and many small chromatin threads and granules dispersed throughout the nucleoplasm, and stain more intensely with haemotoxylin than mesenchymal nuclei (Text-fig. 2, A).Germinal nuclei lie in clusters in syncytium after several divisions, and, after further divisions, bulge into sporocyst lumen as a germinal cyst (Text-fig. 2, B). Germinal cysts are analogous with ovaries. Mitotic figures only located in those parts of sporocyst wall where germinal nuclei occur.
Cytoplasm of syncytium essentially hyaline, faintly granular in irregular patches. Cytoplasm forming a distinct band approximately 1μ to 2μ wide around germinal nuclei, is more densely granular than granular patches of cytoplasm in other parts of syncytium (Text-fig. 2, A).
Terminal region of sporocyst is densely nucleated, containing both germinal and mesenchymal nuclei. Cell membranes are more distinct in this region.
No muscle cells found in sporocyst wall and no movements of sporocyst were observed. No indications of an excretory system, testes or specialised feeding or nutritive branches of the sporocyst were observed.
List of Abbreviations for all Figures
a., anterior sucker; a.m., anterodorsal musculature of sucker; a.s., axial strand; b., beaded region; b.c., brood chamber; bo., body; c., cuticle; c.f., cuticular flap; e.g., cystogenous granules; ci., rudimentary cirrus sac; c.o., cystogenous organ; c.p., cirrus sac; c.t., constriction; c.w., cyst wall; cy., cyst; d., duct of cystogenous organ; d.c., developing cercariae; e., excretory vesicle; eg., egg; e.p., excretory pore; f., furca; fi., fin web of host fish; fl., flame cell; fp., flap of cuticle; f.r., fin ray; g., intestine; g.a., genital anlagen; g.at., genital atrium; g.b., germ ball; g.c., gland cells; g.d., gland cell ducts; ge., genital lobe; gm., gap between groups of muscle fibres; g.n., germinal nucleus; g.p., genital pore; gr., granules; i.m., undifferentiated mass of cells; l., four lipped anterior extremity; l.c., Laurer's canal; l.d., longitudinal excretory tubule; lu., lumen; m., mesenchymal nuclei; m.c., mucus cells; mo., mouth; mu., muscle layer; mus., core of tentacle; n., ganglionic mass; o., oblique muscle fibres; oe., oesophagus; oo., ootype; ovi., oviduct; ov.c., germinal cyst; oy., ovary; p., pharynx; pa., parenchyma; pap., papilla; p.d., posterior longitudinal excretory tubule; pr., prostate cells; pv., pars prostatica; r., semi-retracted tentacle; r.v., left vitelline duct; s., syncytial layer; s.g., Mehlis's gland; s.v., seminal vesicle; t.d., diagonal excretory tubule; t.du., tentacular duct; te., testes; th., thorn of tentacle; ti., tissue of host origin; tn., tentacle; t.s., tail stem; u., uterus; v., vacuolate intestine; v.f., vesiculate floor of sucker; vit., vitellaria; v.r., vitelline reservoir.