Arcella Ehrenberg, 1832 (ref. ID; 3686)
Class Tubuliniea: Order Arcellinida (Kent, 1880) (ref. ID; 6789)
Order Arcellinida Kent, 1980 (ref. ID; 6790)

[ref. ID; 1618]
Test transparent, chitinous, with hexagonal markings, colorless to brown (when old); in front view circular, angular, or stellate; in profile plano-convex or semicircular; variously ornamented; aperture circular, central, inverted like a funnel; protoplasmic body does not fill the test and connected with the latter by many ectoplasmic strands; slender lobopodia, few, digitate, simple or branched; two or more nuclei several contractile vacuoles; fresh water. Numerous species. (ref. ID; 1618)

[ref. ID; 1923]
Shell hemispherical, membrane punctate. Aperture equal to or less than 1/2 of the shell diameter. Two nuclei or more (8 or 10 to 200). Shell generally circular in apical view. Membrane distinctly and densely punctated, brown or yellow in color. Aperture central, circular, sometimes lobate. Protoplasm united to the inside of the shell by delicate threads, epipodia, which are internal pseudopods of a special kind, often retractile, attached to the shell by a small and inconspicuous disc. (ref. ID; 1923)

[ref. ID; 3686]
Shell colourless, yellow or brown; circular or ovoid; in lateral view varying from plan-convex to hemispherical; surface either smooth or punctated, but may be moulded to have angular facets with sometimes develop into spines or prominences; wall composed of numerous alveoli made of a proteinaceous material, arranged in one or more layers; aperture central, circular, with a small collar, usually invaginated and occasionally surrounded by pores. (ref. ID; 3686)


Arcella amphora Van Oye, 1923 (ref. ID; 2230)
Comments; Deflandre (1928) pointed out that Arcella apicata Schaudinn and Arcella amphora are very similar in many points, and considered them to be conspecific, so that the name Arcella amphora must fall as a synonym before the earlier Arcella apicata. (ref. ID; 2230)
Arcella arenaria Greeff, 1866 (ref. ID; 1332, 2110, 2239, 2441, 2522, 3279, 3382, 3686) reported year? (ref. ID; 3536, 3693) or Greef, 1886 (ref. ID; 4737)
Syn; Arcella aureola Maggi, 1888 (ref. ID; 1332) reported year? (ref. ID; 3693); Arcella microstoma Penard, 1890 (ref. ID; 1332) reported year? (ref. ID; 3693)
Description; The shell always circular in apical view, more or less dome-shaped in lateral view. Dorsal tip usually smooth, but very often flattened. The shell yellowish brown to dark brown in color. Ventral surface with dense punctuations not radial symmetrically arranged. The aperture small, circular in shape, its diameter barely reaching 1/5-1/6 that of the shell. The buccal tube obscure. Many small pores, 8-28 in number, distributed along the margin of the aperture in a regular distance but often, in the older specimens, irregularly scattered far from the center of the dorsum. The height of the shell not less than 1/2 diameter of the shell. Neither remarkable border nor bosses around the lateral margin. Many nuclei present: the large ones usually 3 in number and arranged in an equilateral triangle, the small ones not constant in number, varying 3-5, arranged irregularly. The pseudopodia very short, 6 at most, many vacuoles developing along the ectoplasm. (ref. ID; 3536)
The sell is brown, circular and has a conical aboral region. The apertural surface is usually smooth but often has small pores towards the basal collar. The aboral region is smooth and appears to be divided into segments. These divisions are formed by folds on the shell surface that run from the flat crown to the basal collar. The aperture is invaginated, circular, bordered by a lip and about twenty large pores. The pores are often seen to be blocked, and this may account for the difference in numbers between our observations and previous workers. (ref. ID; 3686)
Comments; In the characteristic of having several small pores around the aperture, the present species greatly resembles A. catinus Penard, and in the characteristic of having more than two nuclei, our species has a close relation to A. polypore and A. megastoma. However, our species is clearly different from the former in the lateral features of the dorsum, although some specimens did display a flattened tip on the dorsum. From the latter two, the present species is distinguishable in size, both the shell and the aperture, besides the dominant number of the nuclei. Several cysts were also observed. They are similar in form to the cysts of A. arenaria var. sphagnicola (Deflandre, 1958, p. 119) or catinus. (ref. ID; 3536)
A variety, A. a. var. sphagnicola, was suggested by Deflandre (1928) for larger specimens having reduced shell folding and no apertural pores. Our observations suggest that this is probably a doubtful variety. This species is similar to Arcella catinus, but can be distinguished using the size of the aperture or the ratio Da/Ds (Diameter of aperture/Diameter of shell), and the number of apertural pores. (ref. ID; 3686)
Measurements; The shell 75-80 um in diameter, 38-42 um in height, aperture 12-20 um in diameter. Ratio of the shell: diameter (SD) to height (SH), namely SD/SH= 1.8-2.0. (ref. ID; 3536)
Diameter of shell 79-130 um; depth 21-50 um; diameter of aperture 22-28 um; Da/Ds 0.18-0.22; number of apertural pores 18-24 (n=15). (ref. ID; 3686)
Arcella artocrea Deflandre, 1928 (ref. ID; 6790)
Description; Shell composition is secreted proteinaeous; position of aperture is ventral. (ref. ID; 6790)
Measurements; Shell dimensions (um): diameter 184-216, depth 46-64, diameter of aperture 36-42. (ref. ID; 6790)
Arcella artocrea Leidy, 1876 (ref. ID; 3686) or 1879 (ref. ID; 4737) reported year? (ref. ID; 1332, 1618, 1923, 2329, 3283, 3491, 3693)
Syn; Arcella artocrea Penard, 1902 (ref. ID; 1332); Arcella catinus Penard (ref. ID; 3693); Arcella vulgaris Leidy, 1879 (ref. ID; 1308, 1332); Arcella vulgaris var. compressa Cash, 1905 (ref. ID; 1332)
Description; Height of test one-fourth to one-half the diameter; dome convex; surface mammillated or pitted; border of test everted and rising one-fourth to one-half the height of test; freshwater. (ref. ID; 1618)
With a distinct border. Cytoplasm colored green by chlorellae. Dome convex, mammillated or pitted; basal border everted and rising from a quarter to nearly half the height of the test. Protoplasm bright green, pseudopods colorless. Habitat bogs and Sphagnum ponds. (ref. ID; 1923)
The shell is brown, circular and has a conical aboral region which is often covered by dents or depressions. The basal collar is usually prominent and smooth. The aperture is invaginated, circular, has a small lip and is surrounded by about thirty large and some small pores. (ref. ID; 3686)
Measurements; About 175 um in diameter. (ref. ID; 1618)
Diameter 184-216 um. (ref. ID; 1923)
Diameter of shell 190; depth of shell 57; diameter of aperture 36 um (n = 1). (ref. ID; 3686)
Arcella bathystoma Deflandre, 1928 (ref. ID; 3686) reported year? (ref. ID; 3501, 3595)
Description; The shell is brown, circular with a domed aboral region having several angular facets. The shell surface appears to be either smooth or pitted with numerous small pores. The aperture is invaginated, circular, and surrounded by a small lip. (ref. ID; 3686)
Measurements; Diameter of shell 49-53; depth 28-32; diameter of aperture 13-15 um (n = 2). (ref. ID; 3686)
Arcella catinus Penard, 1890 (ref. ID; 1308, 1332, 1333, 1618, 2329, 2441, 2522, 3686) reported year? (ref. ID; 3501, 3595, 3693)
See; Arcella artocrea Leidy (ref. ID; 3693)
Syn; Arcella artocrea Penard, 1902 (ref. ID; 1332, 2329); Arcella vulgaris Leidy, 1879 (ref. ID; 1308, 1332); Arcella vulgaris var. compressa Cash, 1905 (ref. ID; 1332)
Description; Test oval or quadrate, not circular, in front view; aperture oval; dome compressed; lateral margin with six or eight facets; fresh water among vegetation. (ref. ID; 1618)
The shell is brown, usually circular and has a shallow conical aboral region. The aperture surface is usually smooth but often has small pores around the basal collar. The aboral region is smooth and is divided into segments by folding of the shell surface. The aperture is invaginated, circular, has a small lip and is surrounded by as many as fifty large and small pores. (ref. ID; 3686)
Comments; See Arcella arenaria.
The similarity between A. catinus and A. arenaria has led to some confusion in earlier descriptions. It would appear from the present work that the two species may be distinguished by the size of the aperture and the number of pores surrounding it. (ref. ID; 3686)
Measurements; Test 100-120 um in diameter and about 45 um high. (ref. ID; 1618)
Diameter of shell (Ds) 73-114 um; depth 22-29 um; diameter of aperture (Da) 22-37 um; Da/Ds 0.30-0.33; number of apertural pores 35-50 (n = 6). (ref. ID; 3686)
Arcella conica (Playfair, 1918) (ref. ID; 3686) reported year? (ref. ID; 2683) or (Playfair) Deflandre (ref. ID; 2356, 2564, 3595)
Description; The shell is brown, circular with a domed aboral region. The domed region is depressed to form angular facets which are bordered by prominent folds. The shell is surface appears to be irregular and has numerous small pores. The aperture is slightly invaginated, circular and bordered by a collar. Variation in this species appears to be restricted to the arrangement of the angular folds. (ref. ID; 3686)
Measurements; Diameters 100; heights 97; diameter of aperture 30 um. (ref. ID; 2356)
The diameter of the test was 77 um and the diameter of the pseudostome was 20 um. (ref. ID; 2683)
Diameter of shell 68-76; depth 63-66; diameter of aperture 23-33 um (n = 3). (ref. ID; 3686)
Arcella crenulata Deflandre, 1928 (ref. ID; 3686)
Description; The shell is brown, circular with a domed aboral region. In lateral aspect there usually appears to be a basal collar at the border of the shell. The shell surface is smooth or irregular and has numerous small pores. The aperture is invaginated, circular had has a denticular margin. The species was initially described by Deflandre (1928) as a variety of Arcella vulgaris. We consider that the difference in the shape of the aperture is sufficient to treat A. crenulata as a valid species. (ref. ID; 3686)
Measurements; Diameter of shell 113-160; depth 52-58; diameter of aperture 24-53 um (n = 7). (ref. ID; 3686)
Arcella dentata Ehrenberg, 1830 (ref. ID; 1315, 1618, 1923, 2045, 2091)
See; Arcella stellaris Perty (ref. ID; 3693)
Syn; Arcella Okeni Perty, 1852 (ref. ID; 1315); Arcella stellaris Perty, 1849 (ref. ID; 1315); Arcella stellata Ehrenberg, 1871 (ref. ID; 1315)
Description; Test circular and dentate in front view, crown-like in profile; diameter more than twice the height; aperture circular, large; colorless to brown; fifteen to seventeen spines; in the ooze of freshwater ponds. (ref. ID; 1618)
With teeth or dentate border. Shell having in lateral view the appearance of crown when the points are well developed. Apically stellate or dentate, with 8 to 14 teeth. Habitat bogs and swamps. (ref. ID; 1923)
The ventral side, turned to the substratum, resembles an inverted funnel, with a circular aperture in the centre. The opposite, dorsal side is dish-shaped with flattened vertex, and bears 7-20 spines or ridges; the spines are bent dorsally and more or less evenly spaced around the circumference in a single row. (ref. ID; 2091)
Measurements; About 95 um in diameter, aperture 30 um in diameter. (ref. ID; 1618)
Diameter with the spines 123-184 um. (ref. ID; 1923)
The theca of A. dentata is about 120 um in diameter (107-133 um, n = 25) and about 50 um in height (41-58 um, n = 25). (ref. ID; 2091)
Arcella discoides Ehrenberg, 1843 (ref. ID; 3686), 1871 (ref. ID; 1315, 1618, 1923, 2099, 2147, 2330, 2356, 2498, 3173) or 1872 (ref. ID; 3536) reported year? (ref. ID; 2683, 2873, 3496, 3501, 3595, 3693)
Syn; Arcella discoidea Ehrenberg, 1843 (ref. ID; 1315); Arcella peristicta Ehrenberg, 1854 (ref. ID; 1315); Arcella vulgaris var. discoides Issel, 1901 (ref. ID; 1315)
Description; Test circular in front view, plano-convex in profile; diameter about three to four times the height; test coloration and body structure similar to those A. vulgaris; in fresh water. (ref. ID; 1618)
Without a distinct border. Shell smooth, with a large circular aperture; in lateral view plano-convex with a rounded border. Two nuclei. Common in pond water. (ref. ID; 1923)
The shell generally circular in apical view, more flattened than arenaria in lateral view. Dorsal surface usually rising gently toward the center, but often truncated. The shell, dark brown in color and all of the surface densely punctuated. The aperture circular, its diameter 1/6-1/7 that of the shell, but often with lobate cruciform fulca. Very often many small pores around the aperture. Height of the shell about 1/3 that of the diameter. Usually two nuclei. Neither remarkable border nor bosses around the lateral margin. (ref. ID; 3536)
The shell is yellow or brown, circular, and has a shallow conical aboral region with a basal border or collar. The whole of the shell surface appears to have small pores, although they are less apparent on the basal collar. The aperture is invaginated, circular and bordered by a shallow lip. (ref. ID; 3686)
Comments; The specimens, at a glance, remind us of Arcella vulgaris var. multinucleata Penard, 1928, but clearly differed from it in the small size of the shell (diameter and height), relative size of the aperture and dominant number of nuclei. This species comprise four varieties, of which the present species is identical with difficilis which Deflandre found around Paris. (ref. ID; 3536)
Measurements; Test diameter 70-260 um. (ref. ID; 1618)
Diameter 90-146 um. (ref. ID; 1923)
Diameter 100; aperture diameter 32 um. (ref. ID; 2356)
Diameter of 110; pseudostome diameter of 38 um. (ref. ID; 2683)
The shell 80-90 um, aperture 12-20 um and height 20-40 um. (ref. ID; 3536)
Diameter of shell 83-104; depth 23-30; diameter of aperture 21-31 um (n = 9). (ref. ID; 3686)
Arcella discoides Ehrenberg f. compressa Opravilova (ref. ID; 2555 original paper)
Description; Light yellow test whose apex was pressed inside in all the specimens. These edges were thickened. The same form in the species Arcella arenaria, i.e. A. arenaria compressa is reported by Chardez (1969) from a sample of Sphagnum from Iceland. (ref. ID; 2555)
Measurements; Diameter of test = 98-109; diameter of the aperture = 36-40; height of the test = 33; length of the oral tube = 18 um. (ref. ID; 2555)
Arcella gibbosa Penard, 1890 (ref. ID; 2067, 2109, 2147, 2356, 3686) reported year? (ref. ID; 3595)
Description; The shell is yellow or brown, circular and is domed or hemispherical in lateral view. The apertural surface and the basal collar are smooth, but the aboral hemisphere has a series of regular depressions. The shell surface may be smooth or irregular and has numerous small pores. The aperture is invaginated, circular and has a distinct rim or lip. Variation appears to be restricted to the number or absence of depressions on the domed aboral region (Deflandre, 1928). (ref. ID; 3686)
Measurements; Diameter 90; height 65; diameter of aperture 30 um. (ref. ID; 2356)
Diameter of shell 90; depth 61; diameter of aperture 19 um (n = 1). (ref. ID; 3686)
Arcella hemisphaerica Perty, 1852 (ref. ID; 2067, 2109, 2147, 2236, 2329, 2330, 2356, 2456, 2558, 2564, 2873, 3686) reported year? (ref. ID; 3496, 3595, 3693)
Description; The shell is yellow or brown, circular, and hemispherical in lateral view. The shell surface is either smooth or irregular and has small pores. The aperture is slightly invaginated, circular, and bordered by a lip. (ref. ID; 3686)
Comments; This species was considered by Cash (1905) to be a synonym of A. vulgaris although Deflandre (1928) and subsequent authors have regarded it as a distinct species. There appears to be some variation in the size and shape of the shell, and the degree of invagination of the aperture (Deflandre, 1928). (ref. ID; 3686)
Measurements; Diameter of shell 55-63; depth 23-35; diameter of aperture 11-14 um (n = 7). (ref. ID; 3686)
Arcella megastoma Penard (ref. ID; 1923, 2068, 2234, 2329, 2356, 2683, 3595)
Description; Shell very flattened with a wide aperture, 0.4 to 0.5 of the entire diameter, which varies from 190-365 um. With 36 to 200 nuclei. Habitat marshes and ponds, among algae. (ref. ID; 1923)
Measurements; Diameters of the tests 195-300; diameters of pseudostomes 85-140 um. (ref. ID; 2683)
Arcella mitrata Leidy, 1876 (ref. ID; 1308, 1315, 1618, 1923, 1986, 2564) reported year? (ref. ID; 3693)
Description; Test balloon-shaped or polyhedral; height exceeds diameter of base; aperture circular, crenulated and usually evarted within inverted funnel; protoplasmic body spheroidal, with 'neck' to aperture and cytoplasmic strands to test; six or more slender lobopodia; in fresh water among vegetation. (ref. ID; 1618)
Shell higher than the breadth of the base, mitriform or balloon-shaped. Dome mostly inflated, its summit and sides evenly rounded or mammillated. Aperture not exactly circular but crenulated. Habitat Sphagnum and Utricularia. (ref. ID; 1923)
Measurements; Test 100-145 um high, 100-152 um in diameter. (ref. ID; 1618)
Diameter 100-180; height 100-162 um. (ref. ID; 1923)
Arcella ovaliformis Chardez & Beyens et. al., 1987 (ref. ID; 4738 original paper)
Description; Elliptic shell and aperture. Aperture invaginated forming a short ring, bordered by 14-16 large pores. Shell formed by membrane, bearing fine alveoli. Nuclei 2, each 9-10 um diam. on either side of aperture. On the basis of its flattened shape, and the low depth-length ratio, this species must be placed in the Aplanatae section. (ref. ID; 4738)
Comments; The only other species, somewhat resembling A. ovaliformis sp. nov. is A. oblonga Schaudinn 1898, from East Africa. The differences, however, are clear-cut: the aperture in the latter is not invaginated, its shape in lateral view is elliptic, and it has no pores around the aperture. It is worth mentioning Awerintzew (1906) considered this species as rather doubtful. It has only been observed once. (ref. ID; 4738)
Type locality; The samples were taken on August 12th (M 102) and 13th (M 96, M 97) 1985 in the moss tundra at Martinodden, in the southwestern part of Edgeoya, a high arctic island belonging to the Svalbard archipel. (ref. ID; 4738)
Arcella polypora Penard, 1890 (ref. ID; 3686) reported year? (ref. ID; 1333, 1923, 2588, 3595, 3693)
Description; Regularly plano-convex, with sharp border. Aperture with a very distinct row of pores. With 6 to 200 nuclei. Shell flattened, with a wide aperture. Habitat aquatic vegetation. (ref. ID; 1923)
The shell is brown, circular and has a shallow conical aboral region. The aperture surface of the shell is usually smooth, but the remainder of the shell has numerous small pores. The aperture is slightly invaginated, circular, bordered by a small lip and about sixty large pores. (ref. ID; 3686)
Comments; This species is similar in shape to A. discoides and A. megastoma, but it can be distinguished from them on shell size, apertural size and the distribution or absence of pores around the aperture. (ref. ID; 3686)
Measurements; Diameter 80-150 um. (ref. ID; 1923)
Diameter of shell 112-143; depth 21-30; diameter of aperture 40-48 um. (ref. ID; 3686)
Arcella rotundata var. alta Playfair (ref. ID; 2067, 2356, 3595)
Measurements; Diameter 42; height 24; diameter of aperture 12 um. (ref. ID; 2356)
Arcella vulgaris Ehrenberg, 1830 (ref. ID; 1315, 1335, 1618, 1923, 3686) or 1832 (ref. ID; 661, 5461) reported year? (ref. ID; 2235, 2236, 2238, 2330, 2564, 2683, 2873, 3342, 3496, 3595, 3693)
Syn; Arcella hemispherica Perty, 1849 (ref. ID; 1315); Arcella patens Claparede & Lachmann, 1859 (ref. ID; 1315); Arcella viridis Perty, 1849 (ref. ID; 1315); Difflugia arcella Wallich, 1864 (ref. ID; 1315)
Description; Height of test about one-half the diameter; dome of hemispherical test evenly convex; aperture circular, central; colorless, yellow, or brown; protoplasmic body conforms with the shape of, but does not fill, the test; lobopodia hyaline; two vesicular nuclei; several contractile vacuoles; in the ooze and vegetation in stagnant water and also in soil. (ref. ID; 1618)
Shell dome-shaped. Surface smooth or with regular undulations. Pseudopods long and transparent. Many contractile vacuoles. Two nuclei opposite in position. Habitat ponds, among algae and other plants. (ref. ID; 1923)
The shell is yellow or brown, circular and is hemispherical in lateral view, often having a basal collar. The shell surface can be either smooth or irregular, and usually has numerous fine pores. The aperture is invaginated, circular, and bordered by small lip. The size of the hemisphere and the invagination of the aperture appear to be the usual variation seen in this species. Other differences in shell structure have resulted in several authors describing new forms or varieties, for example, Deflandre (1928) lists eight in his review of the genus. (ref. ID; 3686)
Measurements; Diameter 30-100 um. (ref. ID; 1618)
Diameter 100-152 um. (ref. ID; 1923)
Diameter 110; diameter of pseudostome 29 um. (ref. ID; 2683)
90-130 x 40-82 um. (ref. ID; 3342)
Diameter of shell 104-136; depth 46-56; diameter of aperture 22-32 um (n = 4). (ref. ID; 3686)
Arcella vulgaris f. crenulata (ref. ID; 2356)
Measurements; Diameter 113-124; diameter of aperture 35-38 um. (ref. ID; 2356)
Arcella vulgaris f. undulata (ref. ID; 2356), var. undulata Deflandre (ref. ID; 2330)
Measurements; Diameter 130; height 65; diameter of aperture 32 um. (ref. ID; 2356)
Arcella vulgaris var. angulosa (Perty, 1852) Leidy, 1879 (ref. ID; 1315, 1618)
Syn; Arcella angulosa Perty, 1852 (ref. ID; 1315); Arcella costata (Ehrenberg, 1901) (ref. ID; 1315)
Description; Test smaller, 30-40 um in diameter, faceted, forming a five- to eight-sided figure, with obtuse angles. (ref. ID; 1618)
Arcella vulgaris var. gibbosa (Penard, 1890) G. S. West, 1903 (ref. ID; 1315, 1618)
Syn; Arcella gibbosa Penard, 1890 (ref. ID; 1315)
Description; Test gibbous, surface pitted with circular depressions of uniform dimensions. (ref. ID; 1618)
Measurements; 45-50 um to 100 um in diameter. (ref. ID; 1618)
Arcella vulgaris var. polymorpha Deflandre (ref. ID; 3342)
Measurements; 62-83 x 47 um. (ref. ID; 3342)