world of amoeboid organisms

Menu

Difflugia acuminata, D. pyriformis, D. labiosa, D. nodosa, D. urceolata, D. scalpellum, D. varians
 
From left to right: D. acuminata, D. pyriformis, D. labiosa, D. nodosa, D. urceolata, D. scalpellum, D. varians (all on scale)
 
 

Genus Difflugia Leclerc, 1815

Diagnosis: Testate amoeba with an agglutinate shell, with a terminal aperture that is round, oval, lobed or toothed, but never slit-like, sometimes with a collar or necklace but never with an internal diaphragm. The test or shell is composed of mineral particles, like quartz fragments, or diatom frustules, collectively called xenosomes, that are assembled on structured or sheet-like organic cement. All known Difflugia species acquire their xenosomes from their environment. Many select and arrange these xenosomes according to their size and shape in order to construct a shell with a morphology that is unique to that particular species. The nucleus is usually ovular, but in larger species vesicular. Some species are multinucluated. Some of the larger freshwater  species, living in deeper waters, contain green endosymbionts or zoochlorellae.

Type species: D. proteiformis Lamarck, 1816, but its nature is questionable (Ogden and Ellison, 1988).

Difflugia scheme

The drawing on the right shows the main characteristics of a Difflugia, in this case of D. capreolata. Its pseudopodia are finger-shaped and therefore called lobopodia. They can have different shapes: a stretching pseudopodium, b retracting, c branching and d broad so-called lamellipodium.

 

Remarks: Difflugia is the oldest and most species-rich genus of testate amoebae, with more than 300 species and a lot of subspecies and varieties. Therefore it is called an overcrowded genus (Meisterfeld). However many descriptions are inadequate, based on artificial criteria, one or few specimens, very small variations in size, shape, color and shell material or the lack of data on natural variation of shell characters. As the test is often opaque, cytoplasmic characters as shape and structure of the nucleus are rarely used. Identification at species level is for most species extremely difficult. The problem is not only which characters are distinguishable, but also which are diagnostic? Many times even slight deviations in shell shape have resulted in the establishment of new forms or species, regardless of the range of variability that individual Difflugia taxa may exhibit (Mazei and Warren, 2012). Gauthier-Lièvre and Thomas (1958) divided the genus into ten groups based on the morphology of the shell: lobed, collared, compressed, urceolate, globose, ovoid-globose, elongate, acute angled, horned  and pyriform. Mazei and Warren (2012, 2014) have classified species in species complexes, primarily based on two collections: Penard’s mounted microscope slides and Ogden’s SEM micrographs, both in the Natural History Museum in London.

Ecological conditions play an important role in shell morphology. Bobrov et al. (1999) observed a clear decrease of shell size moving from wet to dry conditions in three different species groups. And spined forms within the genera Euglypha and Placocista consistently occurred in wetter habitats whereas spineless forms, or those with short spines, were more prevalent in drier habitats. They concluded that, in order to maximize the ecological indicator value of the assemblages recorded, identifications should be made at the lowest taxonomic rank possible within these groups.
Difflugia species inhabit very diverse habitats. Many species are common in freshwater sediments or between water plants; others are planktonic with a benthic phase during winter; some live in dry mosses and soil. Lakes of different trophic status (eutrophic, dystrophic or oligotrophic) have characteristic dominant Difflugia species.

Feeding: mainly algae and fungi. Small species like D. minuta or D.  pulex can use bacteria too.

 

 

Recent posts

Polychaos spec.

Polychaos spec. Polychaos spec. Diagnosis: Large amoeba with an irregular more or less polypodial shape during slow locomotion; uroid finely papillated, usually very large fasciculate

Read More »

Spiculophrys

Genus Spiculophrys Zlatogursky, 2016 Diagnosis: Centrohelids lacking silica scales but with numerous thin, pointed organic (without any traces of silica) scales tapering towards acute apices. 18S

Read More »

Acanthocystis drakena

From Zlatogursky, 2016 Acanthocystis drakena Zlatogursky, 2016 Diagnosis: Cells are 21.1-30.5 µm (ca. 26.7) in diameter. Cell is covered with oval plate-scales having a margin

Read More »

Choanocystis symna

From Zlatogursky, 2014 Choanocystis symna Zlatogursky, 2014 Diagnosis: Cell body ca. 6.7 µm in diameter. Axopodia three–five times longer than a cell diameter. Plate-scales dumbbell-shaped

Read More »

Acanthocystis costata

From Zlatogursky, 2014 Acanthocystis costata Zlatogursky, 2014 Diagnosis: Cell body ca 9.5 µm in diameter. Axopodia 2–3 times longer than cell diameter. Length of spine-scales

Read More »

Kinetocyst

Left: ultra-structure of a kinetocyst of Raphidiophrys contractilis); right: two kinetocysts in an axopodium. Kinetocysts In centrohelid heliozoa, extrusomes are called kinetocysts, and are present

Read More »