ON A FKESH WATER MEDCSA I'KOM RHODESIA. 427

On a Freshwater Medusa from Rhodesia.

ByClimlcs L. lioulcngcr, HI.A.,

Lecturer on Zoology in the University of Birmingham.

With Plate 42 and 2 Text-figures.

TJHK material on which this note is based consists of anumber of slides wliich I received from Mr. C. ¥. Rousselet,to whom my best thanks are due for his generosity inentrusting1 me with the description of these valuablespecimens.

Mr. Rousselet had obtained the material from his friend,Mr. R. H. Thomas, who discovered the first specimen of themedusa iu a tributary of the Hunyani River1 in SouthernRhodesia in September, 1908. This specimen was sent toEngland, but, owing to its poor state of preservation and tothe fact that an air-bubble was left in the tube in which it wassent, it arrived in a much damaged and macerated condition.

Mr. Rousseleb wrote immediately to ask for better pre-served material, and a few more specimens were obtainedand sent in December of the same year; these were, unfor-tunately, also somewhat damaged in transit. Mr. Thomasendeavoured to collect more medusas but found that theyhad completely disappeared; he has since left the districtand the chance of receiving further specimens is somewhatremote.

The tubes containing the medusae were accompanied bysome pencil sketches of the living animal, and, whilst con-

1 The River Hunyani (or Hanyani), is one of the largest of thesouthern tributai'ies of the Middle Zambesi.

428 CHARGES ],'. BODLBNGBJt.

gratulating Mr. Thomas on his most interesting discovery, Ishould like to take this opportunity of expressing to him myappreciation of the great trouble which he has taken in his en-deavours to send well-preserved material back to this country.

Altogether four medusas reached me in sufficiently goodcondition for investigation; of these two were almost com-plete, the other two fragmentary, each being represented byit sectant of the umbrella to which a portion of the manubriuinwas attached.

All the specimens were mounted in formalin in cells ringedwith gold size.

A mere glance at these medusas is sufficient to show thatthey belong to the very remarkable genus L i m n o c n i d a , oilwhich the only known species, L. t a n g a n i c t e , 1 was dis-covered by Bohm (1) in Lake Tanganyika in 1883, and for acomplete description of which we are indebted to li. T.(:iiu;Ll]er (2, 3). The medusa was at first thought to bepeculiar to this lake, and the halolimnic theory of the originof Lake Tanganyika was based, at. least in part, on itspresence there.

Since that time L i m n o c n i d a tang-anic£e has been foundin the Victoria i^yanza (6, 10)2 and in the River Niger (8, 9),and Mr.'Thomas's discovery oi' a similar jelly-fish in a tribu-

' In tliis, as in a previous paper (12) on tlie Tanganyika jelly-fish, Ihave adopted Gimtber's amended version of the spelling of tbe specificname of this medusa. When describing Dr. Cnmvington's collection in1907 (10), lie remarked—" This would seem an appropriate occasion foradvocating a more reasonable uniformity in the spelling of this specificname; and although in my original paper I had followed Bohni's spelling,tanganyica?, in accordance with the laws of priority, in the presentcommunication the more usual and shorter form tanganica: isadopted. I have noted tanganyicas, tanganicamis, tanganicensis,tanganyikte, tanganyiuensis, tanganika3, and in Sollas's 'Age ofthe Earth,' x:>. 209, tanganyicoea-! " E. T. Browne (9) has also adoptedthe revised spelling, but I notice that A. G-. Mayer, in his monograph onthe medusa; (11), uses the form tanganjicte.

2 Gunther was able to detect distinct features in the Victoria Nyanzaspecimens, which he regarded as sub-specific in importance; he pro-posed for these the name L. tanganicte var. victoria;.

ON A FBESHWATER MEDUSA FKOM RHODESIA. 429

tary of the Zambesi shows that this remarkable genus mustbe a pretty constant constituent of the freshwater fauna oftropical Africa, occurring as it does in the four principalriver systems of that continent.

L imnocn ida may even have a wide distribution outsideAfrica, for Dr. Annandale, in a recent letter to 'Nature ' (13),announces the discovery of a similar medusa in India. Anumber of jelly-fish were obtained by Mr. S. P. Agharkarfrom small streams in the Western Ghat, these streamsbelonging to a river system which flows across the IndianPeninsula and reaches the sea more than 500 miles away onthe shores of the Bay of Bengal. Dr. Annandale writes :" In the structure oE the manubrium and digestive system,the position of the gonads, the structure of the tentacles andthe form of the umbrella these medusas agree precisely withLimnocnida t auganyicas . As regards generic identitythere can, indeed, be no doubt, and there is nothing in thespecimens before me to suggest even a specific difference.They are not, however, in a particularly good state of preser-vation, having- suffered somewhat in tile post, and the ques-tion of specific identity may be left unanswered until afteran examination of fresh specimens which I anticipate nodifficulty in obtaining at a suitable season."

The medusa) from Rhodesia present a few peculiarities bymeans of which they can be easily distinguished fromL. taiiganicte, and it is my intention to describe them asbelonging to a distinct species under the name of Limnoc-nida rhodesiaa sp. n.

The specimens which I have examined differed from oneanother both in size and in the degree of contraction of thebell. I, therefore, find it convenient to describe the fourindividuals separately.

The most complete of the four medusas before me wasobtained by Mr. Thomas in December, 1908; its generalappearance is very similar to that of the Tanganyika species,the bell having the characteristic flattened shape which oneassociates with the genus.

VOL. 57, PART 4. NEW SEMES. 32

430 CHARLES L. BOULENGER.

The umbrella has a diameter of 6mm. The manubrium, asin L. tanganicas , consists merely of a thin circular bandmeasuring 2"75 mm. across its base, and the mouth is a widecircular aperture, the diameter of which is ouly slightly lessthan that of the whole manubrium.

Four radial canals run from the base of this organ to theumbrella edge, the latter being provided with a broad, some-what muscular velum a little over 1 mm. in breadth.

There are between eighty and ninety tentacles, which arearranged, according to size, in distinct series, the perradial,interradial and adradial ones being the largest. The umbrellaedge of this specimen is much macerated, and it is impossibleto make out the exact mode of origin of the tentacles or thearrangement of the marginal sense-organs.

The second medusa, obtained in September of the sameyear, is of small size, measuring approximately 2"5 mm. indiameter; although badly broken it is in a much more satis-factoiy state of preservation and presents several features ofgreat interest.

The very different degree of contraction of both umbrellaand manubrium renders the animal very unlike the individualjust described. The umbrella margin is much contracted andthis makes the medusa appear comparatively much higher,in fact almost hemispherical in shape. The manubrium alsoappears very different and has the shape of a truncated cone,the base of which measures about 1 mm. in diameter.

The conical form of the manubrium is due to the contrac-tion of its oral extremity, and when this organ is viewed frombelow the mouth is seen to be almost completely closed,appearing as a small opening surrounded by tlie folded oraledge of the mauubrium (PJ. 42, fig. 1).

In possessing an almost closed mouth this individual is ofconsiderable iuterest, in all the described specimens ofLimi iocu ida t angan i c t e the mouth remained wide open,and previous writers have laid great stress on this character;thus Giinther refers to " the wonderfully large mouth whichthe short manubrium seems inadequate to close," and

OX A FRESHWATER, MEDUSA FROM RHODESIA. 431

E. T. Browne, in his description of the Niger specimens (9),remarks that to judge from the appearance of the medusas" the mouth is incapable, owing to the shortness of the lowerwall of the stomach, of completely closing up."

I do not consider the point just dealt with to be one ofsystematic importance. The first medusa I described had awidely'open mouth similar to that of L. tanganicse, and Ithink it highly probable that a more exhaustive study of livingexamples of the latter species will reveal the fact that themanubriuni is capable of great changes in shape. It mustalso be remembered that the specimen I have been describingis a young one, and the figures given by Giinther of similar-sized individuals of h. tanganicas suggest that at this stagethe manubrium has greater powers of contractility than inthe adult.1

Although much torn,, the umbrella edge of this individual isnot at all macerated, and the structure of the marginal regionforms the main distinguishing feature of the Rhodesiauspecies. In this form the "nettle-ring," instead of forming abroad continuous band round the margin of the umbrella as inL. tanganicai , is considerably narrower and, moreover, dis-continuous, the masses of stinging-cells being grouped roundthe bases of the tentacles and giving rise to distinct bulbousswelling's similar to the tentacle bulbs which have beendescribed ia many Trachymedusa3, e.g. Gonionemus murhaclii(PL 42, fig. 2).

The tentacle-bulbs are equally well developed in the thirdof the four medusa) entrusted to me by Mr. Eousselet. Thisindividual is very incomplete, and is represented by a sectaut•of the bell and part of the manubrinin; as in the medusajust described the umbrella-margin is well preserved, and both.show very clearly another structural difference betweenL. rhodesiac and L. tanganiece.

In the Tanganyika species there is no obvious relationbetween the arrangement of the marginal sense-organs andthat of the tentacles, whereas in the Rhodesian medusa) such

1 C f . Giinther (10), p. 646, text-fig. 172.

432 CHABLKS L. BOULHNGER.

a relation between the arrangements of the two sets of organscertainly exists.

Bach oE the smaller tentacle-bulbs bears a single sense-organ, basally situated near the origin of the velum ; on thelarger bulbs a second sense-organ is usually developed,although occasionally it is missing, just as in a few cases asense-organ may fail to develop on one of the smaller tentacle-bulbs (PI. 42, fig. 2).

71.T--

Part of the tunb: of Oli(miilleri), to show a pair of sense-organs developed at the baseof one of the primary tentacles. i?.r. Nettle-ring, t. Tentacle.s.o. Sense-organ, r.c. Radial canal, in.t. Club-shaped marginaltentacle, (x 45.)

This arrangement; of the marginal sense-vesicles recallsthat which occurs in many species of Ol indias , where apairof these sta-uctures is to be found at the base of each of theprimary tentacles (Text-fig. 1).

The structure of the sense-organs seems identical in everyrespect with that of the similar organs meb with in L. t an-ganicse, although they appear to be somewhat larger than inthat species. In this individual there are about thirty tentacles

A FRESHWATER ME DOS A FROM RHODESIA. 433

and thirty-eight sense-organs to the quadrant; the umbrellaof the complete medusa must have measured at least 12 mm.in diameter.

A portion of the manubriiiin is also present, and this showsthe animal to be sexually mature, an ovary being developed asa broad ring round the base of the organ (PI. 42, fig. 5). Theova seem ripe,and uuder high magnification appeal'polygonal

TEXT-FIG. 2.

ex.

Part of the umbrella margin of Limnoonida rhodesire as seenfrom the exumbrellar surface. This figure shows the attach-ment of the tentacle-bases to the exumbrellar surface of thebell. r.c. Radial canal, t. Tentacle, p.t. Per-radial tentacle.ex. Bxumbrellar surface of the bell. (X 45.)

in shape; they are provided with large clear nuclei, each with adistinct nucleolus (PI. 42, fig. 6).

The last of the four slides before me bears a fragment of amedusa, which must have had very nearly the same dimen-sions as the specimen just described. The umbrella marginis too macerated to allow me to make out anything of the

434 CHARGES L. BOULENGEE.

structure of the nettle-ring, or of the arrangement of thesense-organs.

A small piece of the mauubrium is attached to the umbrella,and shows that this individual is also a female; the ovary,however, seems but poorly developed.1

In all four medusas the tentacles are in a good state ofpreservation, and in their structure very closely resemblethose of L i m n o c n i d a t angan icse . As in that species thelarger tentacles are attached to the exumbrella surface of thebell for a considerable distance (Text-fig. 2); they are, however,not deeply imbedded in tlie jelly as in the Victoria Nyanzaspecimens described by Gunther (10), nor could I find distinctprojecting supports, such as Browne figures in the medusa)collected by Budgett in the E,. Niger (8).

The nematocysts are of the same size and shape as those ofL. tanganicfe , and are grouped in distinct batteries, which onthe extended tentacles are irregularly distributed and situatedat the extremities of conspicuous papillse (PI. 42, fig. 3),recalling those which occur on the tentacles of another well-known freshwater medusii, L imnooodium sowerbi i . 3 Asin the Tanganyika species, the neuiatocyst batteries are absentfrom the proximal parts of the tentacles, in which positionhowever, numerous isolated stinging-ceils are to be seenmaking their way to the more distal parts. In the largesttentacles quite a third of the organ is free from uematocystbatteries, and eveu the smallest have these structures absentfrom at least a small bnsal portion.

The above account of the medusas collected, by Mr. Thomasmakes it evident that the two species of L i m n o c n i d a a r eclosely allied to one another, and agree in many essentialfeatures. L. rhodesitE can, however, be readily distinguishedfrom L. tanganicaa by the structure of its umbrella-margin

1 The two gonad-bearing medusas weve obtained by Mr. Thomas inDecember, 1908.

2 C f . E. T. Browne, " On the Freshwater Medusa liberated byMicrohydra ryderi, Potts, and a Comparison with Limnocodium,"' Quart. Journ. Micr. Soi.,' vol. 50, 1906, pi. 37, fig. 3.

ON A FRESHWATER MEDUSA. FROM RHODESIA. 435

with distinct tentacle-bulbs and regularly arranged sense-organs.

When I first examined the Rhodesian medusas these char-acters appeared very striking, and seemed of considerableimportance; the differences, however, seemed much lessconspicuous when the umbrella-margins of the two species wereexamined side by side. I, therefore, made a careful study ofthe marginal region of L. tanganicEe, and have figured asmall portion of the nettle-ring and neighbouring organsof this species for comparison with the similar figure ofL. rhodesias (vide PI. 42, figs. 4 and 2).

The nettle-ring of L. t anganicas has been described asforming a broad, continuous band along the margin of theumbrella; this is certainly quite correct, but it is to be notedthat this band, although continuous, is not of equal thicknessthroughout. The axes of the larger tentacles can be seenthrough the nettle-ring (PI. 42, fig. 4), and on the sides of thesethe latter structure is considerably thickened, so that, althoughdistinct tentacle-bulbs are not formed, they are at leastindicated, a point which seems to have escaped the notice ofprevious students of this medusa. Moreover, these havestated their inability to make out any relation between thearrangements of the sense-oi'gans and tentacles in L . t aug-anicas. A careful examination of the umbrella margin ofthis species has convinced me that such an arrangement doesexist although it is somewhat obscure.

In an adult medusa the marginal sense-organs are sonumerous as to form an almost closed ring ronnd the circum-ference of the umbrella; occasional gaps are, however, left.Now each of these gaps is invariably situated opposite thebase of one of the larger tentacles, and when the sense-organson either side of it are examined it becomes obvious that theyform a pair belonging to the tentacle in question (PI. 42, fig.4 a, a a n d b, b).

The crowded sense-organs between such pairs roughlycorrespond with the smaller tentacles ; the latter are, however,somewhat more numerous because sense-organs are not

436 CHARMS L. BOULENGER.

developed at the bases of the youngest ones (the so-calledmarginal tentacles).

We see then that L. tanganicaa shows traces, not only ofthe tentacle-bulbs of the Rhodesian species, but also of asimilar arrangement of the marginal sense-organs; I think ithighly probable that it has been derived from some medusabearing distinct basal bulbs which carry the sense-organs.

It seems the custom for writers on L imnocn ida to makesome remarks ou the systematic position of this peculiar typeof jelly-fish. Unfortunately the structure of the new speciesdoes not shed much light on the difficult problem of theaffinities of this genus ; the similarity in the arrangements ofthe marginal sense-organs of L . rhodesise and certainspecies of Olindias is perhaps significant, since there seemsa tendency amongst recent writers on the subject to ignorethe manubrial position of the gonads of Limnocnida and toplace the genus together with Limnocodium close to theOlindiadae among the Trachymedusse.

BIRMINGHAM,December 11th, 1911.

BIBLIOGRAPHY.

1. Martens, E. von, and Bolnn, R.—" fiber eine Qvialleim TanganyikaSee, mit Bemerkungen," ' Sitzber. Ges. Naturf. Fr. Berlin,' 1883,p. 179.

2. Giinther, B. T.—" Preliminary Account of the Fresh-water Medusaof Lake Tanganyika," ' Ann. Mag. Nat. Hisfc.,' ser. 6, vol. xi,p. 269, 1893.

3. "A Further Contribution to the Anatomy of Limnocnidatanganyicse," ' Quart. Jovirn. Micr. Sci.,' vol. 36, p. 271, 1894.

4. Gueme, J. de.—" On a Medusa observed by Dr. Tantain in theRiver Niger at Bamakou (French Soudan)," ' Ann. Mag. Nat.Hist.,' ser. 6, vol. xiv, p. 29, 1894.

5. Moore, J. E. S.—' The Tanganyika Problem,' London, 1903, p. 298.6. Gravier. C.—" Sur la Meduse du Victoria Nyanza," ' Comptes

rendus Acad. Sci. Paris,' vol. cxxxvii, p. 867, 1903.7. Goto, S.—"The Craspedote Medusa Olindias, and some of its

natural Allies," ' Mark Anniversary Volume,' New York. 1903, p. 1.

OX A FRESHWATER MEDUSA FltOM RHODESIA. 437

8. Browne, E. T.—"On the Freshwater Medusa, L imnocn idatanganicas, and its Occurrence in the River Niger,"' Ann. Mag.Nat. Hist.,' ser. 7, vol. xvii, p. 304, 1906.

9. "On the Freshwater Medusa, L imnocn ida tanganica;,discovered in the River Niger by the late J. S. Budgett," ' TheWork of John Samuel Budgett,' Cambridge, 190V, p. 471.

10. Giinther, R. T.—" Zoological Results of the Third TanganyikaExpedition, conducted by Dr. W. A. Cunnington, 1904-5 : Reporton Limnoonida tanga-nicEe, with a Note on the Sub-speciesfrom the Victoria Nyanza," ' Proo. Zool. Soc, London,' 1907,p. 643.

11. Mayer, A. G.—' Medusas of the World,' Washington, 1910, vol. ii,p. 369.

12. Boulenger, C. L.—" On some Points in the Anatomy and Bud-Formation of L imnocn ida tanga-nictc," ' Quart. Jonrn. Micr.Sci.,' vol. 57, p. 83, 1911.

13. Annandale, N.—"The Occurrence of a Freshwater Medusa(Limnocnida) in Indian Streams," 'Nature,' lxxxvii, August,1911, p. 144.

EXPLANATION OF PLATE 42,

Illustrating Mr. C. L. Boulengev's memoir " On a FreshwaterMedusa from Rhodesia."

LIST OF REFERENCE LETTERS.

ex. Exumbrellar surface of the umbrella, m. Mouth, man. Manu-biium. w. Nucleus of an ovum, nem. Nematocyst. nein. h. Nemato-

438 CHARLES I . BOTJLENGER.

Fig. 3.—A part of the distal extremity of an extended tentacle ofL. rh o d e si as. This shows the nematocyst batteries situated at the endsof distinct, elevated papillae of the ectoderm. (X 260.)

Fig. 4.—A portion of the umbrella-edge of Limnocnida tanganicajfor comparison •with fig. 2. The sense-organs marked a, a and b, b arepairs developed at the bases of the two tentacles bearing the samelettering, (x 45.)

Fig. 5.—A piece of the manubrium of a mature specimen ofLimnocnida rhodesiie. The ovary is developed as a ring round thebase of the organ. (x 45.)

Fig. 6.—Ova of L. rhodesioe as seen under a higher magnification.(X 260.)