Diatomeae

• Overview
• Photos
• Taxonomy
• Classes
• Sources

Overview

A taxonomic subphylum.

Photos

Taxonomy

The Subphylum Diatomeae is further organized into finer groupings including:

• Class (4): Bacillariophyceae · Bolidophyceae · Coscinodiscophyceae · Fragilariophyceae

Classes

Bacillariophyceae

Diatoms (: (dia) = "through" + t?µ?e?? (temnein) = "to cut", i.e., "cut in half") are a major group of eukaryotic algae, and are one of the most common types of phytoplankton. Most diatoms are unicellular, although they can exist as colonies in the shape of filaments or ribbons (e.g. Fragillaria), fans (Meridion), zigzags (Tabellaria), or stellate colonies (Asterionella). Diatoms are producers. A characteristic feature of diatom cells is that they are encased within a unique cell wall made of silica (hydrated silicon dioxide) called a frustule. These frustules show a wide diversity in form, some quite beautiful and ornate, but usually consist of two asymmetrical sides with a split between them, hence the group name. Fossil evidence suggests that they originated during, or before, the early Jurassic Period. Diatom communities are a popular tool for monitoring environmental conditions, past and present, and are commonly used in studies of water quality. [more]

Bolidophyceae

Bolidomonas is a of unicellular picoplanktonic heterokonts. It was recently (1999) discovered. Genetically it is close to diatoms, but differs morphologically from them. Bolidomonas cells have two flagella, chloroplasts with girdle lamella, and no eyespot. Photosyntetic pigments present in bolydophyte choroplasts include chlorophylls a, c₁, c₂, c₃, fucoxanthin, diatoxanthin, diadinoxanthin. [more]

Coscinodiscophyceae

Order Centrales is a traditional, subdivision of the heterokont algae known as diatoms. The order is named for the shape of the cell walls (or valves or frustules) of centric diatoms, which are circular or ellipsoid in valve view. The valves often bear radially symmetrical ornamental patterns that can appear as dots when viewed with an optical microscope. Some also bear spines on their valves, which may either increase cell surface area and reduce sinking, or act as a deterrant to zooplankton grazers. Unlike pennate diatoms, centric diatoms never have a raphe. [more]

Fragilariophyceae

Order Pennales is a traditional subdivision of the algae known as diatoms. The order is named for the shape of the cell walls (or valves or frustules) of pennate diatoms, which are elongated in valve view. The valves may be linear or oval in shape, and usually bear bilaterally symmetrical ornamental patterns. These patterns are composed of a series of transverse lines (known as striae) that can appear as rows of dots when viewed with an optical microscope. Some pennate diatoms also exhibit a fissure along their longitudinal axis. This is known as a raphe, and is involved in gliding movements made by diatom cells; motile diatoms always possess a raphe. [more]

At least 190 species and subspecies belong to the Class Fragilariophyceae.

More info about the Class Fragilariophyceae may be found here.

Sources

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