Front Cover
 Title Page
 Occurrence of the turbellarian...
 Description of the flatworm and...
 The attack and result
 Conclusions and recommendation...
 Explanation of the figures
 Back Cover

Group Title: United States Bureau of Fisheries Document, No. 869
Title: The flatworm as an enemy of Florida oysters
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00000175/00001
 Material Information
Title: The flatworm as an enemy of Florida oysters
Physical Description: 8 p. (2 leaves of plates) : ill. ; 23 cm.
Language: English
Creator: Danglade, Ernest
Publisher: Govt. Printing Office
Place of Publication: Washington (U.S. Bureau of Fisheries. Doc. 869)
Publication Date: 1919
Subject: Turbellaria -- Florida   ( lcsh )
Oysters -- Diseases   ( lcsh )
Genre: federal government publication   ( marcgt )
non-fiction   ( marcgt )
Statement of Responsibility: Ernest Danglade.
General Note: At head of title: Department of Commerce.
General Note: "Appendix v to the Report of the U.S. Commissioner of Fisheries for 1918."
 Record Information
Bibliographic ID: UF00000175
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 001752326
notis - AJG5276
lccn - 19000030

Table of Contents
    Front Cover
        Page 1
        Page 1a
    Title Page
        Page 2
        Page 3
    Occurrence of the turbellarian in 1916-17
        Page 4
    Description of the flatworm and physical conditions
        Page 5
    The attack and result
        Page 6
    Conclusions and recommendations
        Page 7
    Explanation of the figures
        Page 8
        Page 9
        Page 10
    Back Cover
        Page 11
        Page 12
Full Text

o 0



By ERNEST DANGLADE, Formerly Field Assistant, U. S. Bureau of Fisheries.

During February, 1917, the Bureau of Fisheries and the Florida
Shell Fish Commission made an investigation of a series of oyster
areas on both the east and west coasts of Florida with regard to a
reported destruction of oysters by a parasite, which later proved to
be a polyclad turbellarian, or flatworm. As early as March, 1916,
Dr. R. E. Coker stated, in unpublished field notes, that a worm,
known locally as the "leech," was reported to occur occasionally on
some of the oyster bars in the vicinity of Tampa, and sometimes to
cause within a very short time an enormous mortality among the
planted oysters, and that the fear of the pest served to deter the
oyster planters from extending the cultivated areas. In the latter
part of December of the same year T. R. Hodges, State shell fish
commissioner of Florida, submitted to the Bureau a number of
oysters, taken from the beds near Cedar Keys, affected with the so-
called "leech." The oysters, which had been packed in ice, were
alive when received in Washington, and contained from 2 to 3 flat-
worms each; however, the worms were dead, probably having been
frozen in transit. The attacks of this parasite on oysters in these
two localities, Tampa and Cedar Keys, are the only ones that had
ever come to the attention of the Bureau.
The writer was informed by R. E. Gibson, an oyster dealer and
planter of Tampa, Fla., that the worms, or so-called "leeches," had
been observed attacking the oysters on some of the oyster bars in the
Tampa Bay region at more or less regular intervals during the past
20 years, and particularly during the oyster season 10 years ago.
The worms would disappear entirely from the beds for a period of 2
or 3 years and then reappear, the reoccurrences apparently running
in cycles. Compared with the attack of the season 1916-17, the
previous infestations and mortality were said to have been less
extensive and harmful.
On the east coast of Florida a similar outbreak of the worms was
observed 10 years ago at three or four points on Indian River. The
principal infected localities in that body of water were Indian River
Inlet, Bethel Creek, and Orchid. After a very serious and damaging
attack, from which some oyster bars were practically depleted or
greatly reduced in productivity, the trouble ceased and has not
occurred there since. The oyster bars in the meantime have recov-
ered their normal condition., It is interesting to note that the de-
struction of oysters by turbellarians was reported by David G. Stead
a This information was furnished by E. F. McDonald, a practical fisherman of Port Orange, Fla.
113671-1 3

1 5-5 7



from New South Wales in 1907.a His notes regarding the discovery
of their injurious effect upon oysters are of interest:
A few years ago I found that this worm was known to a few of the oyster farmers of
Georges River, who had repeatedly observed it amongst oysters on various leases, and
that they distinguished it under the name of "wafer." As this name appears to be
fairly suitable, I propose for the future to use it in speaking of this worm. Though,
as I say, the wafer has been known to certain lessees, no definite connection between
the oyster and this worm has been shown to exist, and no satisfactory evidence has
been brought forward to show that the latter was to be added to the already long list
of oyster pests. However, in the light of recent evidence, I think it will be found
that this is a pest; that it is at times to be seriously reckoned with, and that it will be
found to be fairly widespread in our oyster-producing waters.
At the end of July this year [1907], J. W. Swainson, of Georges River, handed to me
for determination a number of examples of the wafer, which, he said, was very plen-
tiful on his leases at that time. No visit was made by me for the purpose of investi-
gating the matter. During the early part of September Fisheries Inspector Latta
brought in a specimen of an oyster (from a lease in the Hawkesbury River) which was
in the last stage of destruction by one of these flatworms, and which contained the
worm itself. This specimen had been handed to Mr. Latta by J. Izzard, who had
stated that the worm was very plentiful on his leases at Bar Island and Pelican Island,
and that apparently it was destroying the oysters. Upon this it was so arranged that
I made a short visit to the locality in question, for the purpose of obtaining more
definite information. At Bar Island I found the wafer present in large numbers, and
some were found actually at work between the valves of the oysters. Large numbers
of gaping shells of oysters only recently killed were to be seen on all hands, while the
same was apparent on Pelican Island (which is submerged at high water). In view
of the very positive evidence obtained at the time, it is only fair to assume that at
least a part of these-if not all, probably a very large percentage-had succumbed to
the attacks of the wafer. I must here point out that although the common oyster
worm (Polydora or Leucodore) was only too abundant on portions of these leases, none
of the recently dead and gaping shells which I examined showed the least sign of its
attacks or of the attacks of the common "Drill" or "Borer" (Urosalpinx), although I
found the latter (previously unrecognized from this locality) to be fairly plentiful.
It is of interest to mention that at the time of my visit the oysters were all "opening
very badly"; that is, they were in poor condition and were likely to remain so until
the advent of a freshet in the river.


The distribution of this turbellarian in sufficient abundance to
attract attention from oystermen, during the oyster season, 1916-17,
appears to have been confined to the western coast of Florida, between
Cedar Keys on the north and Tampa Bay on the south, a distance of
about 110 miles. It was stated that the southern limits had probably
extended, at some of the earlier periods, as far south as Cape Sable,
making an approximate range of 300 miles.
In the vicinity of Cedar Keys, Port Inglis, and Tampa the greater
number of the oyster bars, especially in the more saline districts,
were infested and had suffered to a greater or less extent. The con-
ditions were so bad that, for a time, the industry appeared to be
seriously threatened. The loss, as reported, ranged from 10 to 20
per cent of the stock on some beds to the destruction of one entire
bar. A planted bed of 35 acres in Tampa Bay was attacked by this
worm and the mature and young oysters alike were said to have
been completely annihilated. The bed had been planted just two
years and had given promise of excellent returns.
a David G. Stead: Preliminary Note on the Wafer (Leptoplana australis), a Species of Dendrocoelous
TurbellarianWorm, Destructive to Oysters. Department of Fisheries, New South Wales, November, 1907;
pp. 1-6. (No other references to turbellarians attacking oysters have come to the writer's attention.)


At Port Inglis and Cedar Keys the destruction during the season
was estimated to be about 30 per cent. One or two localities, how-
ever, revealed a mortality as great as 90 per cent, but the excess
should not be attributed to the turbellarian, since many of the empty
shells or "boxes" contained spat which had set before the depreda-
tions of the worms had occurred, the mortality of these oysters being
due evidently to other causes. When the devastation was at its
height the affected oysters, as a rule, contained from 1 to 3 worms,
although as many as 8 or 10 are said to have been taken from a single
oyster. During the early part of the season about 100 oysters per
barrel contained worms, but by February, the time of the examina-
tion, the trouble had abated to such an extent that not more than 1
or 2 worms were taken in 20 barrels of stock. It is worthy of remark
that on the Port Inglis and Cedar Keys bars no small oysters were
found or reported containing worms, nor did any of the empty shells
of the small sizes show any malformations indicating that a defensive
struggle had taken place.

Although this pest is known to the oyster dealers, planters, and
shuckers of Florida as the "leech," it is an animal of very different
type, belonging to the branch of wormlike animals called platyhel-
minthes, class turbellaria, and order polycladida.a Since the general
character and habits of this turbellarian compare closely with the
similar pest found in New South Wales, and described by Dr. Stead,
the name "wafer" would be a more suitable and less misleading one
for common use.
The worm is almost flat, more or less circular in outline, and
measures from about one-half to three-quarters inch in diameter.
It has occasionally been observed, when feeding, to be so distended
that it would cover half the body of the oyster. When disturbed it
usually rolls up into a sort of a tube, the margins then becoming
curled and very irregular. The upper surface is drab to dark-brown
in color, sometimes nearly black, and at times finely stippled with
darker spots; the central portion, posterior to the eyes, is, as a
general thing, of a lighter shade than the remainder of the surface;
when taken from an alcoholic solution and allowed to dry, a whitish
mucus coating is observed. The lower surface is whitish to cream
color. The worm, when removed from the oyster, is soft and slimy,
and on very moderate pressure breaks up or runs into a jellylike
mass, apparently without much structure. When placed in alcohol
of about 75 per cent strength it becomes firm and somewhat leathery.

The turbellarians were found to thrive in only those localities where
the salinity of the water remained comparatively high, and not in
areas where decided changes in density caused by freshets occur at
certain seasons. The temperature is also an important factor in their
activity and even their existence. If the water is chilled considerably
below the normal it may cause their complete disappearance or
a Harry K. Harring, of the Bureau of St ndards and custodian of Rotatoria, U. S. National Museum, is
engaged in a study of the turbellarian, wh li will probably prove to be a representative of a new genus.


perhaps death. During the early part of February, 1917, there was a
decided fall in the temperature throughout the greater portion of the
State and many orange trees, early gardens, and much vegetation
in general were killed; also many small fishes, crabs, and oysters on
the shallower reefs were destroyed. Following this extreme, the
worms practically disappeared from the oyster beds, and relief was
expressed by those engaged in the oyster industry. Just about this
time local rains reduced somewhat the salinity of the water, which
was also an unfavorable condition for the worms.
Speaking of the turbellarian in New South Wales, Stead says:
"Judging by my present data, they appear to be most plentiful
during dry weather (and particularly while mild or high tempera-
tures prevail), when the water of our estuaries is of greater density."
Dry, warm weather appears to be the most favorable condition
for this enemy. The months of their greatest activity on the oyster
bars are stated to be August and September, and if the weather con-
tinues warm, October, November, and December may be included.
The character of the oyster bottoms and the depth of water on
the bars or reefs do not appear to have any direct influence on the
depredations committed by the worms, since they were found active
and damaging at all depths and on all kinds of bottoms, such as sand,
firm mud, or shells.
It is not known how the worm gains admission within the valves
of the living oyster, and we were not fortunate enough, while exam-
ining the beds, to obtain any data along this line. It is probable that
the soft, velvety creature may flatten itself into a very thin wafer-
like form and slowly work its way between the partially opened
valves without producing a reaction on the part of the oyster. Some
oystermen, who have observed the habits of the parasite, are of the
opinion that the entrance is made along the ventral margin or gill
side, about halfway between the hinge and tips rather than at the
tips themselves, since this is near the point where the worm is usually
found. The first reaction of the mantle of an infected oyster takes
place at this mid-portion of the shell. (See figs. 1 and 2.) It is
possible that entrance is made during the larval or immature stage
of the worm, at a time when admission could be more easily gained,
and development completed within the oyster.
Regarding the method of attack the following remarks are made by
METHOD OF ATTACK.--After gaining an entrance between the valves of the oyster,.
the wafer proceeds to wrap itself round the upper part of the oyster, as close to the
great adductor muscle (which so powerfully keeps the two shells shut) as it can get.
It then proceeds to pour out a great amount of thick, stringy, slimy mucus, which per-
haps has the effect of partly digesting the body of the oyster, so as to prepare it for
absorption by the wafer. Certainly in those which have come under my notice, the
adductor muscle, usually the hardest part of the body of the oyster, is, after being
attacked by the wafer, quite soft, although smelling quite fresh.
One aspect of the case which is very puzzling is, as to how the worm gains entry
between the shells of the oyster without the latter "closing down' on it; as, if it did,
the wafer would surely be nipped in two.
The worm is usually found on the right side of the body of the
oyster, near the heart, between the adductor muscle and the anterior


end or hinge. By carefully opening an infested oyster and removing
the right valve, the worm may be observed as a thin sheet, closely
adherent to the meat, and more or less covered with a slimy mucus.
(See fig. 3.) It was stated by the oyster dealer,a who was interested
in this subject, that he had found the worms in about the same rela-
tive position mentioned above, but on the reverse side or between
the meat and lower valve, so that it was necessary after taking off
the upper valve to turn the oyster over in order to see the worm.
It was not determined how long the oyster can successfully with-
stand an attack or whether it is able to recover after an invasion.
It is the opinion of some dealers that the oysters are killed within
two or three days, but this is evidently too brief a period, at least for
the majority of cases. An examination of many of the oysters showed
plainly, both in the meats and shells, that a hard, continuous, and
defensive struggle for existence had taken place. The oysters, which
were alive when opened, were poor, watery, and shriveled, to a degree
depending upon the duration of the plague. Being robbed of its
juices and its vitality probably reduced by secretions of the worm,
starvation and death would ultimately follow. Up to this time no
odor of decomposition was observed.
When carefully examined, the meat and shell often reveal the
successive stages of the battle between the feasting turbellarian
and the helpless oyster. With a slow but continued loss of its life
juices and consequently contracting meat, the mantle gradually
withdraws from the margins, particularly along the ventral side, and
leaves a dark or blackened border or band of shell substance. (See
fig. 4.) As the struggle continues, a thin ridgelike deposit of the
shell substance may form along the gill side about one-half inch from
the edge of the shell, and extend from the hinge to the tips. (See
fig. 5.) At times a second or inner ridge is secreted. (See fig. 6.) The
oyster, now being reduced to a smaller space by additional loss of its
juices, has thus accommodated itself to a still smaller shell cavity.
These ridges are doubtless a mechanical consequence of the shrinkage
of the oyster; they indicate that the attack is persisted in and that
considerable time elapses before death ensues. The ridges and other
deposits are composed, of regular shell material-calcium carbonate,
and conchiolin; nacreous and crystalline layers are both present.
(See figs. 7 and 8.)

1. Although oysters may be able to resist a brief invasion of the
turbellarian, it does not appear that they possess the means to ward
off an assault in harassing numbers, if long continued.
2. After the turbellarian has once gained admission within the
oyster, there appears to be no method of combating the enemy. The
defensive ridges deposited by the oyster afford only a temporary
3. It is recommended that a careful working or cultivation of the
beds in the infested district be carried on systematically, and that
new, air-dried cultch and fresh seed stock be used when possible.
All marine grasses and other objects under which the turbellarian
a Mr. Williams, Cedar Keys, Fla.


may secrete itself or deposit its eggs should be removed from the
vicinity of the bars.
4. When it is desired to select a new area for planting and cul-
tivation, it is advisable, other things being equal, to choose those
localities where the water has sufficient depth to prevent overheating
in summer, and also where the salinity may not attain too great a
degree, as off affluents.

[All figures are two-thirds natural size.]
Fig. 1. Left valve, showing a thin deposit of shell substance along the ventral margin
from hinge to tips, and covering nearly one-half of the inner-surface of the shell. The
deposit had curled and peeled somewhat before the photograph was taken. The shell
is empty. (Taken from Cedar Keys, Fla., Feb. 10, 1917.)
Fig. 2. Both valves, showing the results of the struggle between the oyster and the
worm. Notice the shell deposits, particularly along the ventral margins. Parts of the
meat are still clinging to the shell at the muscle scar. The worm had escaped.
(Taken from Cedar Keys, Fla., Black Point Bars, Feb. 12, 1917.)
Fig. 3. Left valve with the meat, and the turbellarian in position near the adductor
muscle. Notice the shriveled condition of the oyster, and the retreat of the mantle
from the edges of the shell. The worm had contracted to about one-half of its spread-
ing capacity. (Taken from Port Inglis, Fla., Feb. 10, 1917.)
Fig. 4. Left valve with oyster showing the gills. Notice the "ridges near the hinge
and along the ventral margin. The oyster was shriveled and dead. The worm had
escaped. (Taken from Port Inglis, Fla., Feb. 10, 1917.)
Fig. 5. Left valve, showing that the space occupied by the oyster was reduced, be-
fore death, about one-half. Notice the "ridge," beginning at the dorsal margin, then
crossing adjacent to the hinge to the opposite side and extending to the tips. (Taken
from Cedar Keys, Fla., Feb. 10, 1917.)
Fig. 6. Left valve, showing the reduced space occupied by the oyster just previous
to death. Notice the two "ridges" or successive stages of retreat along the ventral
margin, and the spreading out or fan-like condition at the tips. (Taken from Cedar
Keys, Fla., Feb. 10, 1917.)
Fig. 7. Both valves, showing shell deposits of conchiolin and calcium carbonate.
(Taken from Cedar Keys, Fla., Black Point Bars, Feb. 12, 1917.)
Fig. 8. Both valves, showing deposits of conchiolin and calcium carbonate. (Taken
from Cedar Keys, Fla., Black Point Bars, Feb. 12, 1917.)

;......,:, :' ..,.,

U. S. B. F.-Doc. 869. PLATE I.



U. S. B. F.-Doc. 869.







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