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EXCRETORY PRODUCTS OF
PAGURUS SAMUELIS AND
PAGURUS GRANOSDANUS
(Malacostraca: Decapoda)
by
Peter W. Brown
Hopkins Marine Station of Stanford University
Pacific Grove, California
INTRODUCTION
Although the excretory products of many crustaceans
have been analysed and compared, Pagurus have received
little study. Preliminary work revealed a large amount of
urea in the excretory products of hermit crabs. This find-
ing was unexpected, since most other crustaceans excrete
ammonia as the principal product of nitrogen metabolism.
A more complete investigation was undertaken to confirm the
preliminary study.
METHODS
Pagurus samuelis (Stimpson, 1859) and Pagurus grano-
simanus (Stimpson, 1859) were collected from the area around
Point Pinos, the southern and most western tip of Monterey
Bay, California. These crabs were brought into the laboratory
and placed in small (30 ml.) beakers containing 15 ml. of sea
water. The sea water was treated with antibiotics to prevent
the growth of bacteria and decomposition of the nitrogenous
waste products. Terramycin (oxytetracycline; intravenous;
Chas. Pfizer and Co., Inc., New York) and streptomycin sul-
fate (Eli Lilly and Gompany, Indianapolis) were used. The
beakers were covered with cheesecloth to prevent the escape
of the crabs and maintained at 15° C. for 12-18 hours. At
the end of this time the crabs were removed, and the sample
of excretory water was frozen-ferolater analysisater.
The samples to be analysed were removed from the freezer
and centrifuged to remove fecal pellets. A 12.5 ml. volume
of the sample was then treated bytpassage through a 5 ml.
column of Dowex 50Wx 8, in the sodium form, to remove most
of the divalent cations present in the sea water. These
cations precipitate on Nesslerization. The column was then
washed with distilled water to a final volume of 25 ml.
Total nitrogen, ammonia, urea, allantoic acid, and allan-
toin were measured as ammonia by Nesslerization with or
without preliminary treatment. Allantoin was cõnverted toi
allantoic acid bytbasicahydrolysisnandathe allantoic acid
to urea by acid hydrolysis. Urease solution prepared from
urease tablets (Matheson, Coleman, and Bell) was used to
convert urea to ammonia. Distillation of the ammonia
was finally resorted to because of various precipitates that
formed upon Nesslerization. Urease, allantoin, and allantoic
acid were found to precipitate to various degrees with the
Nesslers Reagent. The distillate was collected in 1 ml. of
MI.
O.1 N HCl, diluted 1with distilled water. 3 ml. of Nesslers
was added and after 30 minutes the color was read in a Klett-
Sommerson photoelectric colorimeter, with a blue filter. This
value was compared to a standard curve.
Uric acid was determined by the method of Folini(1930).
RESULTS
The amounts of the various products of nitrogen ex-
cretion are presented in Table 1. While ammonia was the
principal compound excreted from all the crabs tested,
substantial amounts of other nitrogenous wastes were found.
The results suggest the mechanism for dealing with excess
purines is through a total conversion to NH.. Most of the
intermediates in the mmetabolic series for the degradation
of purines are found to some extent in the excretory water of
these animals. The amount of urea excreted showed great
variation; it was an important product excreted by somgcrabs
and was absent from the excretroy water of others. No marked
difference in the excretory products of the two species was
detected.
TABLE 1
Excretory Products of Pagurus samuelis and
Pagurus granosimanus
ALLANTOT ALLANTOTN
UREA
NH,
ACTD
P. Samuelis
67.6*
74.4
10.5
42.0
149.0
120.0
27.0
103.8
101.2
P. granosimanus
22.8
2.0
178
13.4
12.0
217.2
44.6
137.4
34.2
188.4
xAll table values in ug N/ml. of undiluted
excretory water.
URIC
ACTD
2.46
42
.86
.42
1.30
DISCUSSION
Pagurus samuelis and P. granosimanus seem to follow
the pattern set by other crustaceans, i.e. they are
ammonotelic, the principal waste product of nitrogen metab-
olism being ammonia. (See Waterman, and Prosser et al).
The presence of large amounts of urea excreted by some of
the crabs was a surprising result and is a deviation from
the norm established by other members of the class. This
fact suggests more extensive study to determine the extent
of these large excretions of urea in other Pagurids of the
same and different species. If this trend continues, espec-
ially in species of the upper intertidal, it could indicate
that a least one of the necessary metabolic adaptations for
a more terrestrial way of life is possible in this group of
crabs.
SUMMARY
While ammonia was found to be the principal nitrog-
enous excretory product of Pagurus samuelis and
P. granosimanus, substantial amounts of urea,
allantoic acid, and allantoin were also detected.
Small amounts of uric acid are also excreted.
2. Individual crabs showed considerable variation in the
amounts of the various nitrogenous compounds excreted.
3. No difference in excretory products was observed be-
tween the species tested.
BIBLIOGRAPHY
An improved method for the
1. Folin, O.
determination of uric acid in
blood. J. Biol. Chem. 86: 179-
187, 1930.
2. Prosser, Cl Ladd and Frank A. Brown
Comparåtive Animal Physiology,
2nd. edition, W. B. Saunders
Company, Phila. and London.
pp. 135-152.
3. Waterman, Talbot H. The Physiology of
Crustacea, volume 1. Academic
Press, New York and London.
pp. 341-366.
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