54
Algae
grows progressively outward from this position. As a consequence of the different biomineralization strategies, heterococcoliths are more robust than the smaller and more delicate holococcoliths.
Coccolithophorids, together with corals and foraminifera, are responsible for the bulk of oceanic
calcification. Their role in the formation of marine sediment and the impact their blooms may exert
on climate change will be discussed in Chapter 5.
Members of the Synurophyceae (Ochrophyta) such as Synura sp. and Mallomonas sp. are covered by armor of silica scales, with a very complicated structure. Synura scales consist of a perforated basal plate provided with ribs, spines, and other ornamentation (Figure 2.7). In Mallomonas,
scales may bear long, complicated bristles (Figure 2.8). Several scale types are produced in the
same cell, and deposited on the surface in a definite sequence, following an imbricate, often screwlike pattern. Silica scales are produced internally in deposition vesicles formed by the chrysoplast
endoplasmic reticulum, which function as molds for the scales. Golgi body vesicles transporting
material fuse with the scale-producing vesicles. Once formed, the scale is extruded from the cell
and brought into correct position on the cell surface.
Frustule
This structure is present only in the Bacillariophyceae (Ochrophyta), commonly known as diatoms. The frustule is an ornate cell membrane made of amorphous hydrated silica, which displays
intricate patterns and designs unique to each species. This silicified envelope consists of two overlapping valves, an epitheca and a slightly smaller hypotheca. Each theca is comprised of a highly
patterned valve and one or more girdle bands (cingula) that extend around the circumference of the
FIGURE 2.6 Holococcolith of Syracosphaera oblonga.
FIGURE 2.7 Ornamented body scale of Synura petersenii.
Algae
grows progressively outward from this position. As a consequence of the different biomineralization strategies, heterococcoliths are more robust than the smaller and more delicate holococcoliths.
Coccolithophorids, together with corals and foraminifera, are responsible for the bulk of oceanic
calcification. Their role in the formation of marine sediment and the impact their blooms may exert
on climate change will be discussed in Chapter 5.
Members of the Synurophyceae (Ochrophyta) such as Synura sp. and Mallomonas sp. are covered by armor of silica scales, with a very complicated structure. Synura scales consist of a perforated basal plate provided with ribs, spines, and other ornamentation (Figure 2.7). In Mallomonas,
scales may bear long, complicated bristles (Figure 2.8). Several scale types are produced in the
same cell, and deposited on the surface in a definite sequence, following an imbricate, often screwlike pattern. Silica scales are produced internally in deposition vesicles formed by the chrysoplast
endoplasmic reticulum, which function as molds for the scales. Golgi body vesicles transporting
material fuse with the scale-producing vesicles. Once formed, the scale is extruded from the cell
and brought into correct position on the cell surface.
Frustule
This structure is present only in the Bacillariophyceae (Ochrophyta), commonly known as diatoms. The frustule is an ornate cell membrane made of amorphous hydrated silica, which displays
intricate patterns and designs unique to each species. This silicified envelope consists of two overlapping valves, an epitheca and a slightly smaller hypotheca. Each theca is comprised of a highly
patterned valve and one or more girdle bands (cingula) that extend around the circumference of the
FIGURE 2.6 Holococcolith of Syracosphaera oblonga.
FIGURE 2.7 Ornamented body scale of Synura petersenii.