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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

[ref. ID; 6795 (Enrique Lara et al., 2007)]

The eukaryotic super-group Rhizaria (Adl et al. 2005) is a large assemblage of morphologically and ecologically dissimilar organisms, comprising both flagellate and amoeboid forms. They can be phagotrophic, secondarily phototrophic (like the Chlorarachniophyta) or parasitic (such as the Haplosporidia and the Plasmodiophorida). The rhizarian amoeboid foras are characterised by filose pseudopodia, in contrast to the lobose pseudopodia generally found in "true amoebae" belonging to the supergroup Amoebozoa. In addition, the presence of a test is a recurring feature in rhizarians, such as the Foraminifera, Gromiida and the Euglyphida.

Extant members of the Euglyphida are typical inhabitants of soil and freshwater, being most abundant in permanently wet mosses such as Sphagnum. They are chiefly bacterivorous, and seem to play an important role in the food and energy turnover of terrestrial ecosystems (Schonborn 1992). Reproduction is achieved by binary fission; this is evidence that some species at least undergo meiosis and possibly gene exchange (Iudina and Sukhanova 2000; Schonborn and Peschke 1990). They are characterised by a self-secreted siliceous test, made of scales of different size and shape, which are bound together by organic cement. The morphological classification of the species and genera is based mainly on the shape and disposition of these scales.

The order Euglyphida Copeland, 1956 is divided into four families

Paulinellidae, Cyphoderiidae, Euglyphidae and Trinematidae (Meisterfeld 2002). The first two families are characterised by a rather simple scale pattern, while the latter two often show scale dimorphism, which leads to the apparition of specialised structures on the shell, such as spines and pseudostome-surrounding "teeth". Species belonging to the family Euglyphidae secrete tests with an acrostome opening, while species from family Trinematidae are characterised by a ventrally positioned pseudostome.
Molecular phylogenetic investigation on the position of euglyphid testate amoebae date back to 1995, when Bhattacharya, Helmchen and Melkonian (Bhattacharya et al. 1995) demonstrated the position of Euglypha rotunda and Paulinella chromatophora next to the Chlorachniophyta: Cavalier-Smith (1996/1997) added to this group the sarcomonad flagellates; this assemblage of morphologically diverse organisms was later emended Cercozoa (Cavalier-Smith 1998). However, although the position the euglyphid testate amoebae in the tree of life was clarified since then, the phylogenetic relationships within this taxon remained unresolved. Wylezich et al. (2002) first studied the relationships within this group. Their study confirmed a close relationship between all sequenced euglyphid testate amoebae, the monophyly of which is also well supported by the morphology. They also showed that the different morphospecies that could be identified within genus Euglypha using available descriptions did not correspond to monophyletic units. This confirmed the uncertain status of many forms, as pointed out previously by Couteaux et al. (1979) on the basis of morphology. However, the position of the other genera of euglyphids, and particularly of the family Trinematidae, still remained unresolved. The low number of sequences from genera other than Euglypha led to conclusions, which were in contradiction with the morphological data, such as the grouping of the divergent Assulina and Trinema. Finally, the single sequence representing family Trinematidae (Trinema enchelys) branched inside the Euglyphidae (Wylezich et al. 2002), which did not agree with its morphological characteristics.

Taxonomic summary


Rhizaria Cavalier-Smith, 2002

Cercozoa Cavalier-Smith, 1998 emend. Adl, 2005

Silicofilosea Adl, 2005

Euglyphida Copeland, 1956 emend. Cavalier-Smith, 1997

Assulinidae fam. nov.

Definition: testate amoebae with an acrostome test that is composed of elliptic or round plates which are disposed in a regular, alternate pattern. The test is strongly compressed, and the pseudostome is surrounded by a thin organic rim. No specialised type of scales around the pseudostome.
Genera: Assulina, Placocista

Euglyphidae Wallich, 1864 emend. Lara et al., 2006

Definition: testate amoebae with an acrostome test composed of elliptic, sub-rectangular, scutiform, or almost round body plates which are disposed in a regular, alternate pattern. The pseudostome is surrounded by denticulate plates.
Genera: Euglypha, Scutiglypha?