Notes on the Rearing of Chrysaora Isosceles in an AquariumAuthor(s): Maude J. DelapSource: The Irish Naturalist, Vol. 10, No. 2 (Feb., 1901), pp. 25-28Published by: Irish Naturalists' Journal Ltd.Stable URL: http://www.jstor.org/stable/25521911 .

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IRISH NATURALIST, VOL. X. PLATE I.

2

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3 3 4.

DF.VELOPMENT OF CHRYSAORA ISO0CSCELES.

Jo ace, page 25.

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February, I90i. 25

NOTES ON THE REARING OF

CHRYSAORA ISOSCELES IN AN AQUARIUM. BY MAUDE J. DZIAP.

ON June 2 Ist, I 899, 1 picked up a damaged specimen of the jelly.

fish Chtysaora isosceles on the shore of Valencia Harbour, and

placed it in an aquarium for examination. On the following

day I saw numbers of tiny particles moving about in the

water, and found that they were ciliated planule, which had

been liberated from the medusa. On June 27th the planule were attaching themselves to the 'glass and hanging down

from the surface film of the water.

Two days later the tentacles began to develop, showing that

the free-swimming planula stage was over, and that a fixed

hydroid-like stage, known as the Scyphistoma, had commenced.

At first the Scyphistotnme had four tentacles, then four more

appeared, one midway between each of the first tentacles, and

later on eight others to make up the full number of sixteen.

Some of the Scyphistomae had their full number by July 13th.

I kept a large number of these Scyphistomae in an ordinary

I2-inch bell-jar throughout the winter. About twice a week

some fresh sea-water was put in. A supply of copepods was

kept in the bell-jar, but the Scyphistomae, I found, preferred

to feed upon small medusa, such as S'arsia, and little cteno

phores-Pleurobrachia. In December a few of the Scyphis.

tomae budded young ones from the base of the polyp. On April 3rd, I9oo, I saw an Ephyra swimming in the bell.

jar containing the Scyphistomae, which I had reared from the

Chrysaora taken during the previous summer, and on looking

next day five more were found. It was evident that they bad

only just been liberated from a Scyphistoma, as two specimens

were still united. On April 14th I found a Scyphistoma just

beginning to start the process of segmentation, and kept it

under observation. The tentacles of the Scyphistoma were

gradually absorbed, and the animal changed in colour from

white to pink. A series of transverse rings next appeared,

dividing the body into a number of segments. Each segment

developed into an Ephyra. Segmentation began at the anterior

end of the polyp, and proceeded downwards, so that the

Ephyrne were liberated one after the other, but occasionally in A

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26 The Irishi Naturalist. February,

the struggle for freedom two or three came off together, and

separated afterwards. A Scyphistoma in the process of segmentation is known as

a Strobila. In the specimen under observation, Ephyre were

liberated three days after the commencement of strobilization.

The Ephyre when first liberated were pinkish, but soon

changed to a translucent white. They measured aboult 2 mm.

in diameter. The disc or umbrella was flat and divided into

eight marginal lobes, each bearing a sense-organ (tentacu

locyst). The next step was to try the experiment of rearing

an Ephyra up to the adult stage, and to see how large the

medusa would grow in confinement. On April 17th six

Ephyre, liberated on 3rd and 4th April, were placed in a

bell-jar containing some Sarsia tubulosa; the latter were soon

eaten, in spite of their being much larger and more active

swimmers. By April 22nd the largest Ephyra was beginning

to assume its adult form.

The umbrella measured half an inch in diameter, and four

tentacles had developed on the margin. The tentacles when

fully expanded were about 4 inches in length. The circular

mouth of the Ephyra was now surrounded by four oral arms. Their food supply consisted chiefly of small medusee, which

were greedily devoured. The largest of the Ephyrae

(measured on April 22nd) increased in size more rapidly

than its companions, and proved itself to be the survivor of the fittest by eating them. On May i6th the survivor measured

Ji inches across the umbrella. The oral arms, now frilled,

were 24 inches in length. Four more tentacles had appeared, and others were just visible, one on each side of every sense

organ. By May 22nd it had reached the normal form of the adult

(just seven weeks old) having 24 marginal tentacles. The

umbrella measured 24 inches in diameter, and the frilled oral arms 5 inches in length. On June 4th the brown markings on

the top of the umbrella began to appear. The umbrella now

measured 31 inches across, and the oral arms 9 inches. By

June 13th it had become too large for its bell-jar (12 inches

across and 8 inches deep), so it was removed to another I4 inches across and I2 inches in depth, holding when full about

4 gallons of water. At this stage the umbrella was 5 inches

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I9OI. DrmArP.-Rearing oj Chrysaora isosceles. 27

in diameter. On June 2 iSt the umbrella had increased to 64 inches in diameter and 3 inches in thickness; the frilled

oral arms extended to the bottom of the bell-jar. The colouring

of the marginal lobes and the top of the umbrella was now

as bright as in a specimen taken from the sea-a rich dark

brown colour. About July 8th the medusa-13 weeks old-reached its

maximum growth. The umbrella was 9 inches in diameter, the oral arms and tentacles extended to the bottom of thle bell-jar. The gonads were visible, showing quite yellow through the umbrella.

The difficulty of obtaining a sufficient food supply owing to

the stormy state of the weather, and the increased tempera

ture of the water, gradually affected the health of the medusa.

It began slowly to decrease in size, the umbrella became

smaller in diameter, and the oral arms and tentacles shorter.

It spent, too, a great deal of its time at the bottom of the bell

jar bumpingr the top of the umbrella upon the gravel, instead

of swimming round and round at the surface. By August 13th

its condition became critical, and as it was not likely to live

much longer I preserved it in a solution of formaline. The

umbrella had decreased to 6 inches in diameter.

The chief trouble connected with the rearing of this medusa

was to obtain a sufficient supply of food; its appetite was

enormous. I soon found out what kind of food Chrysaora

preferred by placing different pelagic animals in the bell-jar,

and watching the result.

It had a great liking for small Antho-meduse and Lepto

medusre, such as Corymorpha, Margelis, Sarsia, Amphinema,

Phiaiidium, Laodice, Euchilota, &c.; also for the siphonophore

Agalmopsis, and the ctenophores Pleurobrachia and Bolina. It had no objection to Tonzop/eris and Sagitta. There were,

however, two animals it would not touch, even after a few days'

starvation-the antho-medusa Tiara pileaa, and the cteno phore Beroe ova/a. It is well known that young fish are often

found under the umbrella of the large Scypho-medusae,

especially Pilema (Rhizostoma) octopus. One day I put a small

fish, about an inch in length, into the bell-jar. The medusa

caught it and held it for some time in the frills of the oral

arms, but finally let it go without doing any harm to it. I

kept afterwards two small fish for some weeks in the bell AZ2

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23 The Irish Naturalist. February,

jar along with Chrysaora, but it never attempted to catch

them. Copepods and other crustacea were placed in the bell

jar, but the medusa did not eat them. It seems clear that

Chrysaora mainly lives upon jelly-fish, using the term in a

popular sense.

The long marginal tentacles are used for catching animals, and the lightest touch is sufficient to hold securely a small

jelly-fish. The tentacle is then drawn up and towards the frill of one of the oral arms; the frill seizes the captured

medusa and passes it up into the mouth. When Chrysaora was hungry it stretched out the tentacles to an enormous

length and also the frilled arms; but when quite satisfied it

kept both contracted. A good meal consisted of several dozen medusee and ctenophores.

The water in the large bell-jar was changed daily, about one gallon removed and a fresh supply added. The tempera ture of the water in the bell-jar was often taken and compared

with the surface temperature of the sea. The bell-jar stood on a table near a window with an eastern aspect, sheltered from the sun. In the early part of the year the water in the aquarium

was below the surface temperature of the sea. In February as much as 3 to 5 degrees (sea minimum 47.50 F.; aquarium 42? F.) In March the temperature became more equalized, and later on the water in the aquarium was above the tempera ture of the sea. During May and June the aquarium was usually about 3-4 degrees in excess (aquarium 590-62' F.) In July there was a short spell of hot weather, which increased the temperature of the aquarium to 660F., the sea being 640 F.

This was the highest temperature recorded in the aquarium.

Valencia, Co. Kerry.

EXPLANATION OF PLATES.

PLATr I.

Fig. I. Chrysaora isoscelest-Scyphistoma stage, x 25. 2. A Scyphistoma beginning to strobilize, x 25. 3. Strobila stage, showing Ephyrm ready for liberation, x 25. 4. Young Ephyrae just liberated, x Io.

PLATr 2.

Fig. 5. An Ephyra, oral view, X 35. ,, 6. An advanced Ephyra, three weeks Ad, X 21. ,. 7. An advanced Ephyra, four weeks old, x 2i.

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IRISH NATURALIST, V()l. X. PLATE 2.

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L)EVELOPMENT OF CIIRY'SAOIRA ISOSCELES.

To face page 28.

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