Distephanus Speculum: Double Skeletons with One Aberrant Partner

Abstract

Skeletal form is the key to silicoflagellate taxonomy. Variations in skeleton morphology have been frequently described for the genera Dictyocha and Distephanus (Lemmerman, 1908; Deflandre, 1932; Hovasse, 1932; Frenguelli, 1935; Boney, 1973, 1976), and the wide ranging skeletal variations observed with clonal cultures of Dictyocha fibula Ehrenb. underline the potential plasticity of skeleton formation in this species, (Van Valkenberg & Norris, 1970). Sufficient information now appears available to indicate where taxonomic confusions may arise, particularly when single skeletons are observed either in phytoplankton samples or in fossil deposits. Paired skeletons are predivision stages (Gemeinhardt, 1930; Hovasse, 1932; Marshall, 1934; Boney, 1976). The juxtaposition of the two skeletons in this predivision stage allows a more critical assessment of the taxonomic significance of an aberrant form.