The World of Protozoa, Rotifera, Nematoda and Oligochaeta
Assulina
Assulina Ehrenberg, 1872 (ref. ID; 3686)
Rhizopoda (ref. ID; 2032)
Order Euglyphida: Family Assulinidae (ref. ID; 6795 original paper)
[ref. ID; 1618]
Test colorless or brown; ovoid; with elliptical scales, arranged in diagonal rows; aperture oval, terminal bordered by a thin chitinous dentate membrane; nucleus posterior; contractile vacuoles; filopodia divergent, sometimes branching; fresh water. (ref. ID; 1618)
[ref. ID; 1923]
Border of the aperture very thin and finely dentate. Shell covered with elongate-elliptical plates, usually brown in color. (ref. ID; 1923)
[ref. ID; 3686]
Shell brown or colourless; ovoid, oval in transverse section; composed of oval shell-plates; aperture oval or lenticular, bordered by organic cement. (ref. ID; 3686)
Of small size (28-58 um), oval. Brown in color, but clearer than the A. seminulum. Shell oviform, compressed. Plates usually arranged in alternating diagonal rows, or occasionally irregularly. Habitat mosses and Sphagnum; common. Empty tests are numerous nearly everywhere, but living animals are not common. (ref. ID; 1923)
The shell is ovoid, laterally compressed and composed of about two hundred shell plates. The aperture is terminal and surrounded by between ten and fourteen shell plates arranged in a rather irregular manner, most with their minor axis bordering the opening bur often a few have their major axis. The opening is edged with a thin band of organic cement, this band is frequently thickened on the tips of some plates to form tooth-like projections. The shell plates are oval, ranging from 5.8-6.8 um in length and 2.5-3.1 um in width. They are usually arranged in alternate, longitudinal rows, with their major axis parallel to the major axis of the body. However, in some instances the axes of the plates are not parallel with the body and in these cases the general pattern is altered. The aboral extremity is also subject to irregular arrangement of shell plates. (ref. ID; 2293)
The shell pyriform or oviform and flattened. Generally reddish brown or chocolate brown in color, but sometimes transparent. With a lot of obscure small scale-like covering, 2 um in size. Sandy dust very rarely attached to the shell. Without neck. Border of the aperture very thin and finely undulated. At the fundus one large nucleus. The vacuoles 3-4 in number, size 25-50x22-38 um. The aperture 10-13 um. (ref. ID; 3536)
The shell is brown, ovoid, laterally flattened and composed of approximately three hundred shell plates. The aperture is oval, surrounded by shell plates and bordered by a band of organic cement. The amount of cement around the aperture varies, but is often pronounced. Although the shell plates are usually arranged in longitudinal rows they may sometimes appear irregular (Cash et al. 1915). (ref. ID; 3686)
[ref. ID; 6943]
Assulina muscorum is not only a size-polymorphic (Schonborn and Peschke 1988), but also a shape-polymorphic species. A qualitative phenospectrum has been given by Schonborn and Peschke (1988) (see ref. ID; 2032). In the area investigated, four shape types were distinguished, occuring in brown and white Assulina and in both habitats.
Type 1. The maximum shell width is in the top third. The shell is narrow and has only a small aperture.
Type 2. The maximum shell width is in the top third, but the shell and its aperture are broader than in type 1.
Type 3. The maximum width is in the middle. The oral half of the shell is narrower than the upper part.
Type 4. The maximum shell width is in the middle, but the upper and lower halfs of the shell nearly uniform. (ref. ID; 6943)
Reproduction: Two cells united with the pseudostomes and formed a third new shell into which the cytoplasms of both shells flowed. The nuclei fused and the cytoplasm secreted a cyst wall. The cyst was oval and slightly flattened. The nucleus (synkaryon) was readily visible, but we could not determine whether meiosis took place. The shell containing the cyst (cyst shell) was usually thicker (18.7-20.0 um; shell measurement 3) than the normal shell, and the lower part was closed by a thick shell wall. The cyst shell was brownish or brown as in typic Assulina shells. (ref. ID; 6943)
Comments
The shell of A. muscorum is reported as being usually brown but occasionally colourless in the wild, whereas in culture it is mainly colourless. Nevertheless, live animals have a distinct band, probably the 'pigment zone', at the mid-body region which is often so large that it may tend to give colour to the shell. Variation in structure of the shell appears to be limited to the formation of an extra large individual, usually confined to less than three per cent of the population. Such specimens have more than the normal compliment of shell plates but the arrangement is the same. Similar large specimens have been reported in clonal cultures of Euglypha rotunda. (ref. ID; 2293)
Measurements
Length 28-50 um. (ref. ID; 1923)
Length of shell 45-53; breadth of shell 32-48; depth of shell 18-22; diameter of aperture 12-18 um (n=8). (ref. ID; 3686)
The shell is colourless or yellow, ovoid and composed of about three hundred and fifty oval, shell plates. It is laterally flattened and the plates overlap at the margins to give distinct lateral lines. The aperture is oval and is surrounded by shell plates which are bordered by a thin band of organic cement. This species can be distinguished from A. seminulum by size and the sharp tapering of the shell from the mid-body position to the aperture. (ref. ID; 3686)
Comments
This species has been introduced by Penard (1890) as a new species. Later he (1902) brought it as a variety under Assulina seminulum. A. scandinavica, although resembling A. seminulum in some aspects, is showing too many characteristics essentially different from A. seminulum: (a) a broad elliptic transverse section of the test of A. seminulum against the sharp edged section of A. scandinavica; (b) the wide variability of the colour of the test of A. scandinavica, varying from dark brown to nearly colourless and transparent; (c) the dimensions of the test: 90-140 um for A. scandinavica against 67-107 um for A. seminulum. Besides these morphological characteristics A. scandinavica demonstrates preference for an environment of wet mosses in constantly refreshed water; therefore, it has been and restricted to the few environments mentioned above. (ref. ID; 2241)
Measurements
Length of shell 107-114; breadth of shell 102-103; depth of shell 39-42; diameter of aperture 26-30 um (n=2). (ref. ID; 3686)
Body does not fill the test; with numerous food particles; pseudopodia few, straight, divergent, slender, seldom branched; in sphagnum. (ref. ID; 1618)
Of large size (60-90 um), and with rounded shell. Adult forms are chocolate brown in color. Transverse section lenticular. Nucleus large. Pseudopodia few, straight, slender. Habitat Sphagnum and moss in marshy places; common. (ref. ID; 1923)
The shell is yellowish-brown or colourless, ovoid, and composed of approximately three hundred, oval shell-plates. The shell plates are arranged regularly but overlap at the margins to give a distinct lateral line. The aperture is lenticular and usually surrounded by evenly spaced shell-plates, but they may sometimes be arranged haphazardly. On the free margins of these shell-plates is a thin border of organic cement. This border usually surrounds the aperture and appears to be continuous with the cement holding the shell-plates together. (ref. ID; 3686)
Young shells yellowish, older ones light to dark brown, composed oval platelets. Aperture surrounded by overlapping shell platelets with a thin border of organic cement, which holds the platelets together (Ogden & Hedley 1980). Separation between A. seminulum and A. muscorum only by their size, which is in A. seminulum about 1.5x greater than in A. muscorum (Hoogenraad & De Groot 1937). (ref. ID; 4755)
Measurements
60-150 by 50-75 um. (ref. ID; 1618)
Length 60-90, and up to 150 um. (ref. ID; 1923)
Length of shell 72-82; breadth of shell 62-74; depth of shell 25-35; diameter of aperture 21-23 um (n=3). (ref. ID; 3686)
