Chrysophyta specifically the diatoms:

Subkingdom' Phycobionta (algae)

Eukaryotic algae/single or colonial alga; made the transition to land 400 MYA lignin found in Coleochaeta

Division: Chyrsophyta (golden-browns) 6000spp includes the 4 classes:

  • Xanthophyceae: yellow greens
  • Chrysophyceae: golden-browns
  • Bacillariophyceae: diatoms
  • Cryptophyceae: cryptophytes

Given limitations of time, we will only cover the Bacillariophyceae or diatoms

 

Diatoms: 5600 spp...It is estimated that there are between 5,000 and 10,000 species of diatoms. They are found throughout the world in the soil and in both fresh and salt water. The cell walls of diatoms show an intricate beauty that is unsurpassed. They have occurred in enormous numbers leaving vast deposits of cell walls which are used today as a part of several hundred industrial products (e.g., chalk, talc, abrasives, filters).

Habitat:

Diatoms are found in both terrestrial and aquatic habitats.

  • They may be solitary or colonial. Some types secrete a mucilaginous capsule. The mucilage may hold them together as ribbons, chains, zig zag ribbons, and other configurations
  • They are important as they form the basis of the food chain in aquatic ecosystems.

    Aquatic: cold or warm fresh & salt waters esp. predominate in cold marine bodies

    Terrestrial: trees, cliffs, soil, buildings

What is their shape? Pill box

Centric = marine

Pennate = fresh or NONE

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 

 

Features:

Diatoms live in "glass houses." They have beautiful, ornamented, silicified cell walls. This is quite evident if the protoplast is removed by acid or heat

In most diatoms, the cell wall, called a frustule, is made up of pectin impregnated with hydrated silica. Electron microscopy has shown that the fine markings of the diatom walls are actually pores which give the protoplasm access to the external environment.

The walls consist of two overlapping portions (valves) which fit together like a petri dish or a gelatin capsule. The outer valve, the epitheca, fits over the inner valve, the hypotheca. The two valves may be attached to a girdle band instead of overlapping.

The valves are either pennate or centric. Pennate diatoms ( fresh water generally) have bilateral symmetry in valve view. The general outline may be boatshaped or rod-shaped. In the center or the valve of most pennate diatoms is either an unsilicified groove, the rapine, or a hyaline median line, the pseudoraphe. The rapine seems to be associated with the movement of many pennate diatoms.

How do they move?

Desiccated crystals or fibrils stick to surfaces when they are hydrated and when they contract they move the diatom along

Centric diatoms ( marine) have radial symmetry in valve view and lack rapines and pseudoraphes . The outline of centric diatoms is usually circular, oval, or elliptical.

What color are they?

The protoplast of a diatom has a nucleus, a central vacuole and one to several brownish plastids which contain chlorophylls a and c as well as 13 carotene and xanthophylls.

Colors: chl fl + accessory pigments chl c1 and c2 golden brown color due to fucoxanthin, a carotenoid found in brown algae What are the food reserves?

Food is stored as oil or leucosin in vesicles in the cell.= oils, fats, or carbohydrates ( chrysolaminarian)

Why does depositing food in the form of oils make sense in an aquatic creature? consider density effects, translucency, energy content...

How do they reproduce?

Asexual reproduction takes place by nuclear and cytoplasmic division. The daughter ce1ls each have only one wall and half the volume of the parent cell. As a daughter cell enlarges, a new wall develops with the parental wall forming the epitheca Thus one daughter cell will be smaller than the parent. Continued asexual reproduction results in the reduction of their size- Normal cell size is restored by discarding the old walls and reproducing sexually, first forming a zygote and new walls.

Diatoms in a local pond sample