Comparative Spermatogenesis in the Sphaerocarpales. I. Blepharoplast Structure in Sphaerocarpos and Riella

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Abstract
Analysis of the cytoskeletal and locomotory apparatus in spermatids of S. donnellii and R. americana shows that they share an unusual structural characteristic not previously observed in hepatics. The spline, a supportive band of parallel microtubules, commonly has a wider, asymmetric, anterior portion tapering posteriorly to a prolonged, narrow shank of 6 or more tubules. In Sphaerocarpos and Riella the spline anterior comprises a maximum of 20 and 24 microtubules, respectively. However, the shanks of these splines comprise only 2 tubules each, 3 times fewer than has previously been observed. The close morphological similarities in the blepharoplasts of these 2 taxa constitute additional evidence of close phylogenetic affinity, and will serve as the basis for comparison with the putatively spharocarpalean Geothallus as well as with hepatics in unrelated orders.