375

Amoeba taylorae n.sp.

By CATHERINE HAYES, S.N.D., B.Sc, PH.D.(From the Research Department of Notre Dame College, and the Zoology Department,

Glasgow University)

SUMMARY

In material collected from Tannoch Loch, Dunbartonshire, a large free-living,hitherto undescribed amoeba was found. Individual specimens vary in length from420 to 500/x and in width from 70 to 140/x. Viewed over a black background thisamoeba looks dense, white, and opaque, while in transmitted light it has a dusky,almost black, hue, due to the presence in the endoplasm of a large number of smallcrystals uniform in size, slender and pointed at both ends. There is always a uroid atthe hinder end surrounded by bits of debris. The one large nucleus is without akaryosome but has masses of chromatin scattered through the nuclear substance. As arule there is only one large contractile vacuole, but occasionally a few small ones maybe seen at the hinder end. A certain number of nutritive spheres are always present.The author considers this amoeba to be a new species and names it Amoeba taylorae.

SOURCE OF THE MATERIAL

DURING the summer of 1938, while examining material collected fromTannoch Loch, Dunbartonshire, Scotland, and its outflow stream at

Milngavie, I came across a large amoeba which even at a mere glance appearedto differ widely from A.proteus, A. dubia, A. villosa, and A. nobilis, all of whichhad previously been identified from this source by Sister Monica Taylor andall of which were known to me. A large number of A. villosa, a considerablenumber of A. nobilis, and a few A. proteus were present in the particular lotof material, but there was not the slightest difficulty in distinguishing thenew amoeba, for under the low power of the Greenough binocular over ablack background it looked dense, white, and opaque in contrast with thesomewhat translucent appearance of the other amoebae. When placed on aslide and viewed under an 18 mm. or 4-4 mm. objective it was equallydistinct, being of a dusky, almost black, hue. As will be explained later, theseappearances are due to the presence in the cytoplasm of a very great numberof minute crystals.

Throughout the summer of 1938 a few specimens of the amoeba could befound in every lot of material collected from this particular source. In 1939 Ihave records of its occurrence in March, April, July, and October, while itwas absent from what little material I was able to collect during 1940, 1941,and 1942. In February 1943 I had one specimen from material collected onthe 2nd and one from material collected on the 10th. One individual wasseen in the spring of 1952.

DESCRIPTION OF THE AMOEBA

This creature, one of the larger free-living, freshwater amoebae, has oftento be freed from adhering debris with a pair of fine needles. If sometimes it

[Quarterly Journal of Microscopical Science, Vol. 96, part 3, pp. 375-381, 1955.]

376 Hayes—Amoeba taylorae n.sp.

should happen to be spread out more or less fan-like when found, it beginsrapidly to assume a very characteristic shape when placed on a slide. Theshape referred to is elongated, narrow at the hinder end, and gradually widen-ing out in front into a single broad, flat, directive pseudopodium (fig. 1, A).

The tip of this pseudopodium often bifurcates (fig. 1, B), sometimes re-

FIG. 1. A, a living A. taylorae, showing the uroid, contractile vacuole, nucleus, a great numberof small crystals in the endoplasm, and a considerable number of nutritive spheres. B, outlineof A. taylorae, to show debris attached to the uroid, the bifurcation of the anterior pseudo-

podium, and the direction (shown by arrows) of the cytoplasmic stream.

maining divided for a considerable time, sometimes returning to the originalcondition almost at once, while less often the whole of the cytoplasm flowsinto one limb, the other meantime disappearing, thus restoring the morenormal monopodial condition. As a rule there is not more than this one largepseudopodium, there being very little tendency to form lateral pseudopodia.

The average length of the amoeba when it has assumed this very usualshape is about 420/x, though this varies greatly from individual to individual,as I have had specimens measuring nearly 500/i. My records show the widthto vary from about 70 to 140ju..

Hayes—Amoeba taylorae n.sp. 377

At the hinder end there is always a well-marked uroid (fig. 1, A and B),-which never appears elsewhere in this amoeba, a fact differentiating it fromA. villosa in which a uroid may appear at any point of the ectoplasm. Aconsiderable amount of debris, consisting of small pieces of decayed vegetablematter, long strips of Oscillatoria, diatoms, &c, is generally carried with theuroid, and it often looks as if most of this debris consists of the waste in-digestible parts of the food (fig. 1, B).

In accordance with the fixed position of the uroid at its posterior end, theamoeba never, so to speak, flows backwards; that is, the posterior end neverbecomes directive and anterior. When about to change direction the amoebadoes so by letting the anterior tip of the pseudopodium flow to one side orthe other or by pushing out a large lateral pseudopodium into which all thecytoplasm flows; thus the direction may change through a right angle, butthe original uroid persists and is still posterior.

The cytoplasm and its inclusions

The cytoplasm consists of endoplasm and ectoplasm, the latter being veryclear and fairly broad, especially at the anterior end where it pours out inwave-like fashion as the creature flows along. The endoplasm is somewhatcoarse and granular, but it has a rapid, easy flow, especially down the centralregion of the body. This is indicated by arrows in fig. 1, B. There are noectoplasmic folds and therefore the amoeba does not belong to the genus orsub-genus Chaos, which is characterized by such folds (Schaeffer, 1926), butto Metachaos, as do A. discoides and A. kerrii. The uroid consists of fineray-like prolongations of the ectoplasm (fig.i, A and B).

Embedded in the cytoplasm are:

1. The contractile vacuole

There is one large contractile vacuole which occasionally may grow to agreat size, 70, 80, or even 90/11. It is generally situated at the hinder end ofthe amoeba near the uroid, and is always, even when it is well forward, behindthe nucleus. In other large amoebae, e.g. A.proteus, A. discoides, A. lescherae,the contractile vacuole is often alongside, under, overlying, or anterior to thenucleus, as both these structures are carried along in the cytoplasmic stream.The contractile vacuole always bursts near the uroid, and does so very gently;and I have noticed on several occasions that it does not disappear entirely, avery minute droplet remaining to initiate the next vacuole. Although thereis only one large contractile vacuole, it often happens that a number of smallvacuoles lie beneath the uroid near the large vacuole; these may burst separ-ately and vanish, or one or other of them may increase in size and become themain contractile vacuole. Surrounding the contractile vacuole is a well-definedlayer of material of unknown composition and function, which stains slightlywith ordinary nuclear dyes. In A. proteus, A. discoides, and A. lescherae (Taylorand Hayes, 1944) this layer is in the form of blocks resembling in appearancethe chromatin blocks of the nucleus.

378 Hayes—Amoeba taylorae n.sp.

2. The nucleus

The single large nucleus, which is surrounded by a narrow area of clearcytoplasm, has an average diameter of about 30/i, though individual nucleimay be somewhat less or considerably greater in diameter (fig. 2, A and B).Its shape seems to be that of a biconvex lens and hence it appears circularwhen viewed from above and elliptical when seen in side view.

The ground-substance of the nucleus is coarse and gives the impression ofbeing viscid and stiff, while the chromatin masses are large and conspicuousand, as there is no karyosome present, they are scattered evenly through thenuclear substance, only occasionally appearing as a definite layer underlying

, , layer ofcytoplasm ' e .? s~- ...chromatin

; tf£K^ blocks': ,*&?•£"' nuclear,

_v.yvv'<Vr membrane

'-W^ C=^inchromatin

b l o c k s

Scale of figs. A and B

FIG. 2. A, nucleus of ordinary size, with very thin nuclear membrane and chromatin blocksscattered throughout the nuclear substance, B, a very large nucleus with only a trace of thenuclear membrane, but with a distinct layer of chromatin blocks round the periphery. Fig. 2was drawn from specimens fixed in Bouin's fluid and stained in Ehrlich's haematoxylin and

light green. A Zeiss apochromat 2 mm. oil immersion objective was used.

the nuclear membrane (figs. 1, A, and 2, B). Fixed and stained preparationsreveal the nuclear membrane to be thin (fig. 2, A). The nucleus is often observedat the posterior end of the creature, whence it may move slowly forward toabout the middle of the body; here it generally remains stationary while thecytoplasm flows past it rapidly, thus restoring it to its original posterior posi-tion. The slow movement of the nucleus through the rapid cytoplasmic streamand its ability to remain at rest in this stream is indicative of its viscid andrather solid nature. The nuclei of A. proteus, A. discoides (Hayes, 1938),A. lescherae (Taylor and Hayes, 1944), and A. kerrii (Taylor, 1947), whichappear to be more fluid, are carried along rapidly in the cytoplasmic streamand rarely remain stationary.

I have not been able to procure a sufficient number of specimens to workout the nuclear division.

3. Nutritive spheresA certain number of nutritive spheres are always present (fig. 1, A). Gener-

ally these are small, but in two or three individuals examined the sphereswere large and greenish in colour.

Hayes—Amoeba taylorae n.sp. 379

4. Crystals

The most striking feature of this amoeba is the very great number of smallcrystals which it normally contains (fig. 1, A). As already mentioned, it is thepresence of these crystals that causes the amoeba to appear opaque in reflectedlight and dark in transmitted light. Most of the crystals are slender andsharply pointed at both ends, but the points and edges of many of them arerounded so that they appear elliptical. As in the other amoebae, the crystalsdissolve in the process of fixing and dehydrating.

Food of the amoeba

As far as I have been able to ascertain, this amoeba is not a diatom-feeder,though the material from which I have obtained it is exceedingly rich in manyforms of diatoms and swarms with A villosa, a heavy diatom-feeder; it isoften possible to count as many as 20 diatoms (of various varieties) in thecytoplasm of one individual. Flagellates and ciliates seem to be the principalfood organisms. Occasionally, however, especially in the early part of the year,the amoeba's numerous food-vacuoles contain spherical bodies, golden brownin colour. This is also true of A. nobilis and A. villosa, and especially A. hug-onis. After it was ascertained that these bodies were not encysted spores, thematerial was submitted to Professor E. G. Pringsheim, who identified thespherules for Sister Monica Taylor as consisting of a very hard core of achemical substance that he could not identify, covered with a layer of carotene.Pringsheim and Horasse (1950) show that masses of pigment of varying sizeshaving the same composition as the eye-spot occur in a variety of E. gracilts.Pringsheim expressed the view that the cultures containing Euglena thusaffected were not in a healthy condition. The question arises, how do theamoebae obtain these spherical bodies ? Do they ingest the E. gracilis, partlydigest it, and get rid of the carotene bodies by defaecation ? Sister MonicaTaylor (1952) could not decide the question for A. hugonis. She never foundthe golden spherules apart from the living animal.

The fact of its not being a diatom-feeder is beneficial from the point ofview of bringing the amoeba under laboratory culture conditions, as flagellateand ciliate food is much more easily produced all the year round in thelaboratory than are diatoms.

Life-historyNot finding the amoeba in large numbers has prevented me from collecting

any facts about its life-history, but I have had two or three small amoebaewhich might very well be its young stage. I hope to evolve a technique forkeeping the amoeba under laboratory conditions and so be able to elucidateits life-history.

DISCUSSION ON THE IDENTIFICATION OF THIS AMOEBA

When consulting the literature with a view to the identification of theamoeba just described I was impressed by the resemblance between it and

380 Hayes—Amoeba taylorae n.sp.

an amoeba identified in Kansas by M. Anthony Payne (1930) as A.granulosa.A sub-title to her paper records the fact that this is the third record of theappearance of A. granulosa, i.e. 'Griiber's Rare Ameba'. Gruber's record wasmade in 1885, and he gave the name to a small amoeba ('von ungefahr 0,03 mm.Durchmesser'), of which he gives very few details. The second record of thisamoeba was that of Penard in 1902. A glance at Gruber's figure was sufficientto convince me that the amoeba which I have described is not Gruber's 'RareAmeba'. Penard's (1902) account is much fuller than Gruber's (indeed, I failto see how Penard could have thought that the amoeba he described wasidentical with Gruber's A. granulosa), and many points, such as the size, thecharacter of the crystals, and the general appearance of the amoeba causedby these crystals are in accordance with my description, but he states thathis amoeba has a spherical nucleus and large pseudopodia in different partsof the body, while he makes no mention of the presence of a uroid. Payne'sspecimens were smaller than Penard's, yet she agrees with him on other detailsexcept that she says that few lateral pseudopodia are formed during loco-motion and emphatically adds that a 'uroid is not present and the amebanever carries debris'.

Both these authors figure their amoeba and, while the general appearanceand in particular the anterior portion of Payne's fig. 5 does resemble myamoeba, the posterior portion of all her figures and the whole of Penard'sfigure differ from my findings. Cash (1905) describes an amoeba from HaleMoss, Cheshire, which he calls A. proteus var. granulosa, but from his figuresit is quite evident that my amoeba bears little resemblance to it and even lessto Leidy's (1879) fig. 4, pi. I, which Cash considers to be the same speciesas his. Payne considers that Cash's figures were drawn from A. proteus orA. discoides and in this I agree with her, especially in view of the fact thatunder certain physiological conditions both these amoebae may be very muchpacked with crystals. The 'mulberry-shaped caudal extremity', which Cashrefers to and figures, is not a uroid but a temporary condition of the ectoplasm,such as may often be seen in all the large amoebae with which I am acquainted.

To sum up, although resembling A. granulosa in some respects, the amoebadescribed in this paper differs from it in having a biconvex nucleus, a perma-nent posterior uroid, and a great tendency to the monopodial condition whencreeping. In view of these outstanding characteristics and believing that ithas not hitherto been recorded, I propose to call the present species Amoebataylorae, in dedication to Sister Monica Taylor, who has devoted the researchof her lifetime to the genus Amoeba, its species, habits, and culture.

DIAGNOSIS

This amoeba was found in a freshwater loch to which there was a constantinflow of clean water and a similar outflow. The loch was also well stockedwith various kinds of water weeds. In size the amoeba may reach 500/x longby 140p. at the broadest part. The shape is generally elongated and monopodial,

Hayes—Amoeba taylorae n.sp. 381

the anterior end being broader than the rest of the body. The posterior endalways possesses a uroid which generally has debris attached to it. The ecto-plasm is fairly voluminous, especially at the anterior tip. The endoplasm ispacked with small, slender-pointed crystals and hence is very dark in colour.There is one large contractile vacuole, which generally occupies a posteriorposition; occasionally there may be a few small vacuoles near the uroid. Theone large nucleus (about30/x in diameter) is biconvex; it has no karyosome butblocks of chromatin are scattered through it. Sometimes a layer of chromatinblocks lines the thin nuclear membrane. There are no longitudinal foldsin the ectoplasm; in this it resembles A. discoides and A. kerrii and differsfrom A. proteus and A. lescherae. It belongs to Schaeffer's group Metachaos.I consider it a new species and name it Amoeba taylorae.

REFERENCESCASH, J., 1905. The British freshwater rhizopods and Heliozoa, 1,47-48. London (Ray Society).GROBER, A., 1885. 'Studien iiber Amoben.' Zeit. wiss. Zool., 41, 186.HAYES, C, 1938. Quart. J. micr. Sci., 80, 459.LEIDY, J., 1879. Freshwater rhizopods of North America. Washington (Government Printing

Office).PAYNE, M. A., 1930. 'Metachaos granulosa in Kansas; third recorded appearance of Griiber's

rare Ameba.' Kansas (University Science Bulletin).PENARD, E., 1902. Faune rhizopodique du Bassin du Letnan. Geneve (Libraire de l'lnstitut).PRINGSHEIM, E. G., and HORASSE, R., 1950. Arch. Zool. exp. gen., 86, 499.SCHAEFFER, A. A., 1926. 'Taxonomy of the Amoebas.' Publ. Carnegie Inst., 24, No. 345.TAYLOR, M., and HAYES, C, 1944. Quart J. micr. Sci., 84, 295.

1947- Ibid., 88, 99.1952. Ibid., 93, 427.