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Basso et al.: Lithothamnion crispatum Hauck 151

Figs 23–26. Detailed anatomy of the tetra/bisporangial conceptacle pore plate structure of Lithothamnion crispatum Hauck from Marettimo
Island (Sicily).
Fig. 23. Longitudinal section through an empty tetra/bisporangial conceptacle showing double indentation and minimum thickness of the
roof, resulting from pore cells collapse (arrows). LM photograph, DMF8 slide 2. Scale bar 5 100 mm.
Fig. 24. Detail of pore plate depressions across a tetra/bisporangial conceptacle roof. Note a pore canal bordered by filaments shorter
than the regular surrounding roof filaments, that are topped by already disintegrated rosette cells (u and arrows). LM photograph,
FMM3 slide 5. Scale bar 5 25 mm.
Fig. 25. Oblique view of a mature tetra/bisporangial conceptacle pore canal (p) bordered by seven already disintegrated rosette cells (1–7)
giving the surface a depressed appearance. SEM photograph, stub 4894b5. Scale bar 5 10 mm.
Fig. 26. Section through a mature tetra/bisporangial conceptacle pore canal (p). Each filament of pore cells is composed of remains of the
uppermost disintegrated rosette cell (u), a wedge-shaped cell (w) and two squat to elongate cells (labelled 1 and 2). SEM photograph, stub
4894b5. Scale bar 510 mm.

This morphology does not occur in the examined material Woelkerling (1995) the tetrasporangial pore canals bor-
of L. indicum, and it is not reported in published accounts dered by a rosette of degenerated cells were recognized to be
of L. indicum and South African and Australian L. a diagnostic feature in the delimitation of a Lithothamnion
superpositum. Only after the contribution of Wilks & species (for L. indicum). The same character was used by

r
Fig. 20. Longitudinal section through a buried tetra/bisporangial conceptacle showing remains of sterile filaments (sf), and the reappraisal
of growth of roof cell filaments to overgrow the old conceptacle chamber (white arrows). Note remnant of pore plug (black arrow). LM
photograph, CMF1 slide 6 (Marettimo Island). Scale bar 5 100 mm.
Fig. 21. Mature tetra/bisporangial conceptacle roof in surface view. Note depressions (arrows) occupied by a central pore that in turn is
surrounded by five to seven disintegrated rosette cells. SEM photograph, stub 4894b5, (Marettimo Island). Scale bar 5 200 mm.
Fig. 22. Tangential section showing central pore canals (p) of a tetra/bisporangial conceptacle bordered with five to seven rosette cells
(labelled 1 to 7). LM photograph, DMF2A slide 1 (Marettimo Island). Scale bar 5 25 mm.