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6.3), and animals (Table 6.3; Figures 6.4 and 6.5) will be more closely characterized (a good short overview can be found in Campbell et al. (2018)). Apparently, the protozoa do not form a monophyletic clade as formerly assumed, but several independent evolutionary lineages. Traditionally, algae, and sometimes even fungi and bacteria, have been included in plants. As can be seen from Figures 6.1 and 6.2, only the metabionta with red algae, green algae, and land plants forms a monophyletic unit. Fungi cluster with Opisthokonta and thus much closer to animals and then to plants. Among animals, the Protostomia have now been separated in Ecdysozoa and Lophotrochozoa on account of molecular and anatomical data (Figure 6.4). According to the rules of cladistics, only monophyletic groups should be accepted. This requires a restructuring of some of the groups of organisms that had been grouped together, such as protists, mosses, fishes, and reptiles (Lecointre and Le Guyader 2007).
Table 6.1 Important groups of protists (model organisms or diseases caused by pathogens).
| Major protist clades | Characteristics | Example |
|---|---|---|
| Tetramastigota | Secondary loss of mitochondria | |
| Diplomonadida | Two separate cell nuclei | Giardia |
| Parabasalia | ||
| Trichomonadida | Undulating membrane | Trichomonas |
| Euglenozoa | Flagellates with or without photosynthesis | |
| Euglenophyta | Paramylon as storage polysaccharide | Euglena |
| Kinetoplastida | With kinetoplast | Trypanosoma (sleeping sickness) |
| Chromalveolata | With chloroplasts from secondary endosymbiosis | |
| Alveolata | Alveoli under the cell surface | |
| Dinoflagellata | Shell from cellulose plates | Pfiesteria |
| Apicomplexa (Sporozoa) | Apical complex for penetration of hosts | Plasmodium (malaria), Toxoplasma |
| Ciliata (ciliates) | Cilium for movement and nutrient uptake | Paramecium |
| Stramenopilata or heterokonts | With trailing and flimmer flagellum | |
| Oomyceta | Hypha; cell walls from cellulose | |
| Bacillariophyceae (diatoms) | Glassy; walls separated into two | Pinnularia |
| Chrysophyceae (golden algae) | Two flagellate cells | Dinobryon |
| Phaeophyceae (brown algae) | Brown accessory pigments | Laminaria |
| Metabionta | With chloroplasts from primary endosymbiosis | |
| Rhodobionta (red algae) | Without flagellate stage; phycoerythrin | Porphyra |
| Chlorobionta (green algae) | With chloroplasts (similar to land plants) | Chlamydomonas |
| Charophyceae | ||
| → Land plants | ||
| Unikonta | ||
| Amoebozoa | With sheet‐like form pseudopods | Amoeba |
| Mycetozoa (slime mold) | Saprophyte; amoeboid stages form colonies | Physarum, Dictyostelium |
| Opisthokonta | Protruding flagellum | |
| Fungi (Ascomycetes, Basidiomycetes) | Cell walls from chitin, saprophytic | Saccharomyces cerevisiae (yeast) |
| Amanita phalloides (deadly agaric) | ||
| Choanoflagellata | With microvilli | |
| → Metazoa (animals) | ||
The red, brown, and green algae were previously grouped with the plants; due to new molecular systematics, a new order has been proposed.
Important model organisms are given in bold.
Figure 6.2 Phylogenetic relationships between protists and transition to plants and animals.