Bacillariophyta Flashcards
Volutin granules
Diatoms accumulate lipids and volutin.
Volutin granules accumulate in the cytoplasm and constitute a reserve of inorganic polyphosphates.
The number and position of the volutin granules constitute a systematic character.
Pennate diatoms: two large chloroplasts, plate-like, parietal and often lobed
Centric diatoms: many small discoid chloroplasts, lobed
Red: epivalve: older and bigger than hypovalve
Green: Cingula: silicious rings (girdle band) located between the valves
Blue: hypovalve: younger and smaller than epivalve
Differences in cingulum structure
Small one:
Centric diatoms:
AA = radial
BB = valvar
Big one:
Pennate diatoms:
AA = apical
BB = valvar
CC = transapical
Valvar plane lies parallel to the valves, with an outline dependent on the shape of the valves in “valve view”
Apical plane traverses the long axis of the frustules from end to end (apex to apex)
Transapical plane lies perpendicular to the apical plane, traversing the frustules from side to side along the shorter dimension of the frustule
pennate diatoms with raphe on both valves or only one
the other valve may have a clear central area= pseudoraphe
Raphe can be central or eccentric
Central ends of raphe
Polar ends raphe
Loculate Areolae
Areolae of centric diatoms can assume the appearance of hexagonal chambers (LOCULAE) with a partially close outer surface (roof), characterized by the presence of a large round hole, called foramen
tangential arrangement Areolae
Radial arrangement Areolae
The areolae in the pennate diatoms can be arranged in rows to form the STRIAE
Left to right: parallel, radiate, lineate parallel, lineate radial
Most centric and Araphidean pennate diatoms have a RIMOPORTULA, a special wall organelle, represented by more or less elongate tube passing through the valve, which in the internal side of the valve shows an opening similar to two lips.
This structure is also called LABIATE PROCESS. Its function is related to the secretion of mucilaginous polysaccharides
FULTOPORTULA that is not compressed internally
ocellus = structure involved in the secretion of mucilaginous material. It consists of an elevated siliceous plate, finely perforated and surrounded by a hyaline rim.
In Centric diatoms and some Pennate diatoms
The mucilage secreted by the ocellus is used to anchor cells to the substrate or for adhesion of cells in a colony.
A study carried out on the genus Skeletonema has shown the existence of numerous genetically and morphologically distinct species within what was considered a single cosmopolitan and opportunistic species, Skeletonema marinoi.
benthic diatoms or periphyton
Single cells anchored to the substrate with whole valve
benthic diatoms or periphyton
Erect cell colonies arranged to fan, anchored by mucilaginous pads
Cells anchored to the substrate by long mucilaginous stalks
benthic diatoms or periphyton
Cell chain
meroplanktonic or ticopelagic diatoms
Temporary members of plankton
They are often pennate diatoms living loosely attached to the substrate.
With turbulence they are dragged into open waters and they continue to live like plankton
