Joseph Leidy (1879) Freshwater Rhizopods of North America. U.S. Geological Survey of the Territories, Vol. XII, pp. 277-295.



The Foraminifera, though constituting the most extensive and important order of the Rhizopods, are almost exclusively marine. A single well-known genus, Gromia, is represented by several species, inhabiting salt and fresh water.

Greek, bios, life; muxa, mucus

Initial form spherical, but incessantly changing, consisting of a glairy, colorless, finely granular protoplasm, which has the power of expanding and extending itself in any direction, and of projecting pseudopodal filaments, which freely branch and anastomose; a circulation of minute granules in currents along the body and pseudopods; contractile vesicles numerous and minute, and occurring both in the body and pseudopods. A nucleus present or absent.

Plates XLVII, figs. 5-12; XLVIII.

Body at rest, spheroidal, oval, or botuliform; in motion, of ever changing form, --centrally spheroidal, or elliptical, discoid, cylindroid, fusiform, triangular, quadrate, band-like, or dividing into several portions, --with pseudopodal prolongations, usually as filaments, mostly bipolar, of very variable form and length, branching and anastomosing so as to produce more or less intricate nets, often expanding into perforated patches. Composed of pale granular protoplasm with oil molecules, and numerous minute contractile vesicles appearing at the surface of the body and along the pseudopodal extensions. Nucleus when present large, distinct, clear or faintly granular. Vacuoles few or none.
Size. --Exceedingly variable.
Locality. --Sphagnous swamps, in bog-water. New Jersey and Pennsylvania.

In the Proceedings of the Academy of Natural Sciences of Philadelphia for April, 1875, I published a brief notice of a curious organism, under the name of Biomyxa vagans. I first discovered it in water with aquatic plants and sphagnum, from the border of Absecom pond, New Jersey, collected in the autumn and preserved in the house during the winter. The same thing I again found in sphagnum, obtained the following August, in the same locality, and in September, on Broad Mountain, Schuylkill County, Pennsylvania. Subsequently I observed specimens collected with sphagnum at Kirkwood station on the Camden and Atlantic railway.

Biomyxa vagans, as represented in figs. 5-12, pl. XLVII, and pl. XLVIII, is a colorless body of ever clanging and most variable form, consisting of a glairy, colorless, finely, granular protoplasm. From a usually more or less central mass or body it spreads itself into a sheet of irregular form, giving off pseudopodal extensions, which branch and anastomose with one another.

Biomyxa moves slowly, incessantly, and evenly, and never for a moment remains the same. The body mass of protoplasm composing it may spread more or less uniformly from the initial spheroidal form, or it may spread unequally, or divide and extend in any direction. Frequently it becomes narrowly extended at one or both poles, becomes more and more elongated into a cord, which may expand into a band, or may divide and extend into several divergent cords or bands. The whole or different portions may expand and become very thin, even to such a degree as to break into fissures and circular holes.

The pseudopods appear as long, tapering extensions of the body protoplasm, often forking, and with the terminal branches as exceedingly delicate filaments. Contiguous branches frequently anastomose and form nets, which here and there, by expansion, assume the aspect of thin patches with circular holes. The pseudopods are quickly produced, and as quickly modified or withdrawn.

A circulation of granules takes place along the course of the pseudopodal extensions of Biomyxa as in Gromia. It occurs both outwardly and inwardly at the same time in the trunks and larger branches, but in one direction only in the finest. In the flow, frequent fusiform accumulations of protoplasm are produced along the pseudopodal extensions, and these sometimes expand into patches or become secondary centres for the emanation of pseudopodal filaments.

In Biomyxa there is not the slightest distinction between endosarc and ectosarc, the whole structure being a homogeneous, pale and finely granular protoplasm, with variable proportions of minute oil molecules, with fewer, large, darkly defined granules, probably also oil-like in character. It contains numerous minute contractile vesicles, commonly ranging from 0.002 mm. to double that size, and rarely reaching quadruple the same. They are usually best seen and readily recognized by their characteristic movements --slow enlargement, sudden collapse, and reappearance --along the borders of the body and in the forks and nodal expansions of the pseudopods.

Rarely distinct vacuoles, independently of the contractile vesicles, and much larger, are to be seen within the body mass of Biomyxa The round holes which are often produced by the expansion and rupture of portions of the protoplasm or by the closure of meshes in pseudopodal nets are to be distinguished from the true vacuoles.

Biomyxa vagans occurs of very variable size, and sometimes appears so devoid of a definite centre, and without nucleus or other conspicuous element, that I have supposed it was perhaps nothing more than a detached fragment of Gromia.

It has also been a question with me whether to regard it as a true rhizopod or whether to view it as the plasmodium of a fungus. In structure and habit, so far as observed, it seems to accord with the latter rather than with the former, though I have not detected a coalescence of individuals in Biomyxa. [The researches of Bary, Cienkowski, and others show that the spores of the little fungi of the family Myxogastres emit flagellate cellules, which subsequently lose the flagellum and assume the appearance and movements of Amoebas. By continued growth and coalescence, a number of the amoeboid cellules form together a branching and reticular layer of protoplasm, retaining its motory power, and named the "plasmodium" by Cienkowski. The plasmodium finally produces the spore-bearing fungus.]

Cienkowski [Archiv f. mikros. Anatomie, 15, 1876] has described several organisms, related with the latter, of which he regards one as a 'fresh water plasmodium,' while the others are viewed as Rhizopods, under the names of Vampyrella vorax and Arachnula impatiens.

The character of Vampyrella has already been given; the diagnosis of Arachnula is as follows: body naked, colorless, without nuclei, with one or more contractile vacuoles; pseudopods but little branched, sometimes anastomosing, usually springing by thick cords from any part of the surface of the body [Ibidem, 27].

In the same memoir, under the head of Naked Rhizopods, Cienkowski describes a form with the name of describes a form with the name of Gymnophrys cometa, [ibidem, 31*] which resembles Biomyxa, as represented in fig. 12, pl. XLVII, and figs. 7-9, 13, 14, Pl. XLVIII. The former, however, differs in having no contractile vesicles. In this respect, likewise, Biomyxa differs from the nearly related Leptophrys of Hertwig and Lesser [Ibidem, 57, 1874].

*In an excellent compilation of "Recent Contributions to our Knowledge of Fresh water Rhizopods," published in the Quarterly Journal of Microscopic Science, 1877, 349, Mr. Archer expresses an opinion in regard to Gymnophrys which accords with an early impression of my own in relation to Biomyxa. He remarks "that the figures of this Sarcodine remind one not a little of a portion of the mass of a Gromia become isolated and detached by some readily conceivable force, having wandered too far from the headquarters.''

As represented in fig. 6, pl. XLVIII, Biomyxa closely resembles the Amoeba correcta of Schultze [Ueber d. Organismus d. Polythalamien, 1854, 8, Taf. Vii, Fig. 8], from the Adriatic.

One of the earliest observed specimens of Biomyxa vagans, represented in fig. 1, pl. XLVIII, occupied, as first seen, a nearly semicircular space, about 0.6 mm. by 0.4 mm. The main protoplasmic mass extended from a common base in three bands, of which the intermediate one was longest and tapering as it was resolved into divergent pseudopodal branches; while the lateral bands expanded outwardly, and presented large circular holes previous to branching. The pseudopodal extensions freely anastomosed with one another. Small contractile vesicles appeared in many places, both in the principal bands and in the pseudopods. The median band and base contained numerous minute fusiform desmids, all of the same kind.

The protoplasm of the main bands exhibited a faintly striate appearance, perhaps due to an arrangement of granules occasioned by currents. Circulation was observed in different directions at the same time, as indicated by the arrows in the figure.

The organism gradually changed its shape, becoming a single band, then a central elliptical disk, etc. Large angular spaces included in the anastomosis of the pseudopodal extensions would slowly diminish, assume a circular form, and continue to decrease until they seemed to be vacuoles, or in their final closure as if they were contractile vesicles. The pseudopodal filaments were rather quickly projected, and sometimes as quickly contracted and entirely withdrawn. Occasionally they would appear tortuous, or would be seen with a slow, waving, or feeble, lashing movement.

Circulation, indicated by the motion of the granules, occurred along the course of the pseudopods, often in a reverse direction on the two sides of the same filament. Feeble movements, circulatory as well as contractile and expansile, were also seen in the body mass of the creature. Preserved until the following day, it presented no essential change, excepting that it had completely discharged all the desmids previously noticed.

In the same drop of water containing the individual just described there was a very much smaller one, which I supposed might be a fragment of the former. When detected, it presented an elliptical body prolonged into pseudopodal extensions at the opposite poles, as seen in fig. 2, and after a little the body appeared to run along one of the pseudopodal extensions to the end, like a drop of water flowing upon a string, when the creature assumed the shape seen in fig. 3. From the side of the body, in the latter condition, there projected a delicate pseudopod, which was noticed to vibrate slowly toward the main one.

The successive changes of shape of Biomyxa are sufficiently rapid often to render it difficult to delineate the exact forms. Figs. 5 and 6, pl. XLVII, represent two such changes in one individual, and figs. 7-9 three changes in another individual. Fig. 10 represents a third individual accompanying the preceding. The arrows indicate the general direction in the circulation of the granules. Figs. 4-6, pl. XLVIII, represent successive, changes of another individual. As first seen, it was regarded as a minute worm casting; but after a moment its movements and extension of pseudopods indicated its true character.

The material containing the specimens above described, consisting mainly of sphagnum, was collected from the edge of Absecom pond, New Jersey, in September, 1874, and was preserved in a glass-covered case during the winter. The Biomyxas were noticed in association with a multitude of minute, bright-green, one-celled alge, in a transparent jelly attached to the side of the glass case contiguous to the sphagnum covering the bottom of the latter.

At no time had I the opportunity of observing Biomyxa take food of any kind, and rarely have I noticed food within the animal. On one occasion I saw an individual which attracted my attention from its having entangled in its pseudopodal net two active, green Euglenias. These were watched with much interest, under the impression that they bad been captured as food; but, after much wriggling, they both disengaged themselves, and escaped.

Fig. 12, pl. XLVII, and figs. 7-9, pl. XLVIII, represent four views of an individual, exhibiting the chief successive forms assumed in the course of an hour. The specimen was obtained, with others of the same character, in wet sphagnum, from the cedar swamp of Absecom, collected in August, 1876.
Organisms exactly of a like character to those above described I also obtained in sphagnum collected on Broad Mountain, Schuylkill County, Pennsylvania, in September, 1876. Figs. 10-14, pl. XLVIII, and fig. 11, pl. XLVII, represent six successive changes of an individual of the kind, as observed during one hour and twenty minutes.

None of the specimens above described or indicated contained any trace of a nucleus, and my impression of Biomyxa, as derived from the observation of these, was that it would form a member of the order of Monera, notwithstanding its possession of contractile vesicles, which are also considered as being absent in the latter.

In April, 1877, in material from a sphagnous swamp near Kirkwood station on the Camden and Atlantic railway, I found an organism agreeing with the former in all respects, except that it contained a distinct nucleus. This was globular and distinctly and uniformly granular. An individual of the kind, exhibiting three successive changes of form, is represented in figs. 18-20, pl. XLVIII.
With the nucleated specimens, others were detected without nuclei, mostly smaller, and looking as if they might be fragments of the former. Three successive views of an individual of this character are represented in figs. 15-17.

Nearly at the same date with the last observations, and under circumstances almost exactly similar to those in which I originally discovered Biomyxa vagans, I found an organism which I have supposed to 'be the nucleated form or condition of the latter. It was detected in a clear jelly, among numerous minute desmids, some of which were crescentoid and others straight and fusiform. The creature, of which a number of examples were noticed, appeared in general of a more compact or less translucent character than Biomyxa as commonly seen, and though of very changeable form appeared less disposed to produce those extreme changes observed in the latter. Fig. 21, pl. XLVIII, represents an individual of the kind, and figs. 22-25 represent four successive changes of form of a second individual. The body was composed of colorless granular protoplasm, with numerous, scattered darkly defined granules. The nucleus was large, globular, and clear, and contained a nucleolus. Mostly, it was central, though frequently displaced from this position in the successive changes of shape of the body. Several contractile vesicles occupied the borders of the latter, exhibiting the usual characteristic movements. None of the specimens contained distinct food, though occasionally colorless vacuoles, apparently different from the contractile vesicles, were observed among the contents. An individual, shortly after being noticed, was seen to discharge a large oval mass with granules, as represented in fig. 22.