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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Microchlamys

Microchlamys Cockerell

Rhizopoda: Testacea: Order Testacealobosa De Saedeleer, 1934: Eulobosa: Family Microcoryciidae De Saedeleer, 1934 (ref. ID; 7500)
Subclass Testacealobosia de Saedeleer, 1934: Order Arcellinida: Family Microcoryciidae (ref. ID; 7745)

[ref. ID; 1923]
Shell membrane simple. Aperture circular. One nucleus. One species. (ref. ID; 1923)

[ref. ID; 7745]
Remarks; The genus Microchlamys is included in the family Microcoryciidae which is placed in the Order Arcellinida and Subclass Testacealobosia de Saedeleer, 1934 in the most recent classification of Protozoa (Levine et al. 1980). With this there is no dispute because the body is enclosed in a test (=shell) external to the plasma membrane and glycocalyx. Nevertheless, the inclusion of the family Cochliopodiidae within this Subclass now appears to be unwarranted. The external coverings described by Bark (1973) and Pussard et al. (1977) cannot be considered to represent a rigid test, and are more accurately defined as modified glycocalyces. Similar external coverings to those described for Cochliopodium and Gocevia have recently been reported for several naked amoebae, for example specimens of Mayorella have glycostyles or scales (Hollande et al. 1981; Page 1981) whilst several species have a mucous-like glycocalyx (Page 1978, 1983; Page & Baldock 1980; Page & Kalina 1984). These two genera only differ significantly from other naked amoebae by having a distinct polarity for the extrusion of pseudopodia, the covering being apparently absent from this region. It cannot be described as a distinct aperture, as observed in testate amoebae, but the extrusion of pseudopodia at this point and the rounding up of the main cytoplasmic body beneath the external covering represents a good imitation. In addition, the cytoplasmic organisation is also similar, with the nucleus and dictyosomes occupying a dense, central position and the anterior leading region being clear and mainly vacuolar. Comparison between the three genera Microchlamys, Cochliopodium and Gocevia shows that Microchlamys differs from the other two by having a distict shell which has a regular shape and structure, the cytoplasm being enclosed within a membranous sac that lies inside the shell and is secured to it at intervals, and this second structure has a defined central aperture on the aboral face. As both Cochliopodium and Gocevia are considered by Page (1980) to have a flexible covering in close contact with the plasm membrane, and which when the amoeba is in locomotion covers only a valuated dorsal surface, it is concluded that these two genera lack a rigid shell and should be included in the subclass Gymnamoebia Haekel, 1862 'without test' (see Levine et al. 1980). Whether the polarity and pseudopodial behaviour exhibited by them are sufficiently defined characters to warrant a distinct Suborder within the Subclass, or can be accommodated within an existing Suborder, remains to be decided by those more familiar with this group. (ref. ID; 7745)
  1. Microchlamys patella Claparede & Lachmann, 1885 (ref. ID; 1923, 2097, 2423, 2435, 7500) or 1859 (ref. ID; 7745), (Claparede & Lachmann, 1859) Cockerell, 1911 (ref. ID; 3173, 3595)
  2. Microchlamys sylvatica Golemansky, Skarlato & Todorov, 1987 (ref. ID; 2031)

Microchlamys patella Claparede & Lachmann, 1885 (ref. ID; 1923, 2097, 2423, 2435, 7500) or 1859 (ref. ID; 7745), (Claparede & Lachmann, 1859) Cockerell, 1911 (ref. ID; 3173, 3595)

Descriptions

Shell circular in dorsal view, with large aperture. Pseudopod usually single. One nucleus, 1 contractile vacuole. Habitat mosses in swamps. (ref. ID; 1923)

Shell: The shell is usually circular, with a shallow convex inverted saucer-like shape, between 31-48 um in diameter and 13-16 um deep. A small skirt is often seen at the shell margin which appears to be uneven and possibly flexible. The mains surface can be smooth or have an uneven bumpy structure, with some indication of a regular pattern. The skirt being thinner usually has a patterned surface even if the general body of the shell is smooth. Empty shells viewed from underneath show a more distinct pattern, suggesting that the inner surface of the shell is probably thinner than the outer. The whole shell may be transparent, light yellow or brown, although brown shells often have a margin which is less dense in colour even if the shells are empty. The general asumption is that colour is dependant on age, lighter shells being associated with younger animals (Archer 1877; Cash & Hopkinson 1905). The concave side of the shell is usually seen as large a opening giving the impression that the width of the aperture is just less than total diameter. Nevertheless, in living animals the cytoplasm is enclosed in a thin membrane which is attached to the inner surface at intervals and has a median opening for the projection of pseudopodia. In testate amoebae the aperture is defined as the opening through which pseudopodia are extended, therefore it follows that the aperture in Microchlamys is the opening in the membrane. The uncertainty regarding the correct apertural opening, as expressed by earlier workers, is due to both the cytoplasm and enclosing membrane being lost in empty shells and it is as such that they appear to be most commonly found. The shell wall is composed of a single layer of numerous small hexagonal units which are joined together to form a honeycomb-like network. Similar units seen in shell wall of Arcella have been called 'thecagenous granules' by Netzel & Grunewald (1977). These units are bound closely together to give an apparent continuous coat covering the internal and external surfaces of the shell. The internal surface is usually smooth but the external surface may sometimes be uneven, occasionally having small pore-like openings in it. Each unit is about 450 nm in width and depth, with the dividing walls being about 60 nm thick. All the walls of each unit appear to be of a similar thickness, although, the external surface is sometimes seen to be slightly thicker than the others. At the base of the inner dividing walls there are small, basal usually circular openings about 20 nm in diameter. The presence of these internal openings was first seen in sectioned material. An oblique section of the shell wall shows that both complete hexagonal units and those with one or more broken walls are present. Examination of these 'breaks' indicates that they have rounded not torn edges, suggesting that they are not artifacts. This was later confirmed by randomly fracturing whole shells and inspecting the fractured edges. Such fractures showed that the breaks are circular openings and a constant feature throughout the whole shell. Specimens subjected to ion beam etching for the briefest time, are abraded sufficiently to reveal the patterned structure of the honeycomb network. Nevertheless, where the specimen touches the hard surface of the stub abrasion is more severe, and is seen to create artifacts by concentrating or rolling-up the wall material. The wall material is formed into elongate sausage-shaped structures and gives the underside of the external wall, as seen between the network pattern, a pitted appearance. Ion etching as a technique for fragile organic material clearly has its faults, and must be used in conjunction with other methods whereby the results can be cross-checked. A recent description of the shell of Microchlamys patella from the marine psammon, given by Golemansky & Couteaux (1982), suggests that it is covered by numerous pores. This type of structure has not been seen on living animals or empty shells and is presumed to be an artifact produced by the effect of salinity. (ref. ID; 7745)

Measurements

Diameter 40 um. (ref. ID; 1923)

Microchlamys sylvatica Golemansky, Skarlato & Todorov, 1987 (ref. ID; 2031)

Descriptions

The shell is semitransparent, yellow brownish, with a darker central part. Older specimens are brown. In its dorsal view the shell is usually circular. In live specimens the shell is sometimes folded underneath and has a coccon-like appearance. The shell form of live specimens resembles a plate in its lateral view with a slightly convex ventral part. Empty shells have a flat ventral side. Shell structure is similar to that of M. patella according to the description of Penard (1902) and Ogden (1985). Dorsal surface punctuation can be distincted better in the central part of the shell, while in its light peripheral margin the sculpture is fine and the shell appears smooth. A thin, non-structural, flexible and transparent membrane is observed on the ventral side of the shell. The pseudostome with an uneven circular form is situated medianly, size approx. 1/3 of the shell. The cytoplasm of living animals occupies the central part of the shell in a spherical pattern. Epipodes were not observed. Lobopodes are clearly distincted when the shell is folded on its ventral side. Pseudopodes were not observed in specimens sticked to the substrate. The nucleus is of a vesicular type, deficient of chromatin. Observations by scanning electron microscopy show that the central part of the dorsal side of the shell is slightly depressed and contains approximately radial ridges. Shallow pits, about 0.6 um in diameter, are scattered along the whole dorsal surface, however near the edge of the shell these pits appear to be less noticeable. The dorsal surface of the test including the bottoms of the pits is covered by a filamentous coat. Pores of different diameters perforating this coat are evident in some pits, some of them covering an area so large that they fill up almost the entire bottoms of the pits. (ref. ID; 2031)

Measurements

Shell sizes of 113 specimens measured varies from 140 to 175 um. (ref. ID; 2031)