Premium
MOTILE CELL ULTRASTRUCTURE AND THE CIRCUMSCRIPTION OF THE ORDERS ULOTRICHALES AND ULVALES (ULVOPHYCEAE, CHLOROPHYTA)
Author(s) -
Floyd Gary L.,
O'Kelly Charles J.
Publication year - 1984
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.1002/j.1537-2197.1984.tb12491.x
Subject(s) - ulvophyceae , biology , thallus , ultrastructure , chlorophyta , botany , dinophyceae , algae , chlorophyceae , ecology , phytoplankton , nutrient
We have examined the motile cell ultrastructural features of several green algal species having filamentous or foliose thallus morphology and probable affinities with the Ulvophyceae, and compared them with the structural, reproductive, and life history features known for these taxa. We separate the algae studied into the orders Ulotrichales and Ulvales on the basis of consistent variations in terminal cap and proximal sheath structure that correlate well with life history patterns and certain features of sporangial and gametangial structure and development. Body scales are present only in certain members of the Ulotrichales. Both orders encompass a variety of thallus forms, demonstrating parallel evolution of thallus morphology. Flagellar apparatus features common to all the motile cells examined include 180° rotational symmetry, counterclockwise absolute orientation, the positioning of the basal bodies in an apical papilla, and the presence of one or more sets of striated bands associated with the X rootlets. Additional features that are usually present include basal body overlap and orientation roughly perpendicular to the long axis of the cell during forward swimming, striated distal fibers, and a single, striated, microtuble‐associated component underlying each two‐membered rootlet. These similarities indicate to us that the two groups are closely related members of the Ulvophyceae. We suggest that the Ulotrichales is the most primitive ulvophyceous assemblage known, but that all groups studied have advanced features relative to those supposed to have been present in the ancestral members of the Ulvophyceae.