Feeding in Ophelia assimilis
Anne Billingsley 2
INTRODUCTION
Ophelia assimilis (Tebble) is reported by Hartman (1969) to occur
in the sandy beaches of Central California. The worms live as isolated
groups in mid-intertidal regions which are exposed during medium and low
tides but covered during high tides. The sand they inhabit is clean and
relatively free of conspicuous organic detritus, lending interest to the
source of their food supply. Studies done on a closely related species,
Thoracophelia mucronata (Treadwell) by McConnaughey and Fox (1949)
suggest that these worms feed on organic material adsorbed to sand grains,
possibly as colloidal micelles, and other fine particles adhering to the
sand or closely associated with it. Wilson (1948a), when studying larval
settlement in Ophelia bicornis (vide de St.-Joseph) observed that relatively
little organic material adsorbed to the sand grains is sufficient to
support the nutritional requirements of this species and that the "clean¬
est" sand will nourish these worms adequately. However, substrate
analysis and feeding behavior have not been examined in detail, save
a single study on carotenoid uptake in T. mucronata (Fox et al., 1948).
Observations of the anatomy of O. assimilis show this worm has
a simplified pharynx unequipped to capture prey, lacks filter-feeding
or plankton-concentrating structures, and has reduced parapodia and
setae. This simplified anatomy and the animal's restriction to organically
impoverished substrates suggests that their feeding habits and food supply
are similar to those of T. mucronata and O. bicornis
Feeding in Ophelia assimilis
Anne Billingsley 3
The studies reported here were conducted to determine whether or
not O. assimilis is a sand-eater, deriving all of its nutritional
requirements from the organic carbon adsorbed to the sand grains. It
further sought to determine the qualitative and quantitative nature of
the food of this animal, the percentage uptake of total organic carbon
as well as specific nutrients, and examined the efficiency of nutrient
utilization. Determination of selectivity of food substrate was also
investigated, along with transit times of sands coated with natural and
test materials.

MATERIALS AND MEIHODS
Specimens of O. assimilis were collected from a sandy beach adjacent
to the Hopkins Marine Station in Pacific Grove, California. Animals were
maintained in running sea water in sand for no more than four days before
use in experiments. Sand samples from the worms' habitat were collected
a few hours prior to analysis, and were sifted through a.495 mm Standard
kler screen to a size found to correspond to the particle size ingested
by the worm. Samples of sand were washed with distilled water prior to
analysis. Feces were collected from fresh worms which were hand-washed
to remove adhering sand particles and placed in Petri dishes on an inert
substrate of ground colored glass approximating particle feeding size.
Dishes were filled with Instant Ocean (Aquarium Systems, Inc., Eastlake,
Ohio), to avoid organic carbon deposition from sea water, and the dishes
Feeding in Ophelia assimilis
Anne Billingsley 4
were placed on a sea table overnight with sea water running to maintain
a temperature of 14.5°0. The feces were pipetted from the substrate and
washed thoroughly with distilled water. Fecal material from 82 worms was
used for analyses.
Organic carbon content of sand and feces was determined using the
wet ashing procedure described by Strickland and Parsons (1968) and
expressed as micrograms carbon/ml wet material.
Protein was determined using the method by Lowry et al. (1951) and
a standard of Bovine Serum Albumin, Armour Fraction V.
Polysaccharide carbohydrate was determined on a sodium hydroxide
digest of the sand following the method of Somogyi (1934), and subsequently
analyzed by the colorimetric method of Dubois et al.(1956). The method
was originally designed for the estimation of glycogen in tissues and
the application of the method to analysis of sand provided an estimation
of the larger insoluble carbohydrate fraction.
Lipids were determined by weight after extraction with petroleum
ether.
RESULTS
Dissections of freshly collected worms revealed guts filled with sand
for nearly the entire length of the worm. All of the sand taken from
the guts of worms was of a similar size and could pass through the mesh
Anne Billingsley
Feeding in Ophelia assimilis
of a .495 mm Standard Tyler screen. Only 3% of the sand in their habitat
is of this size. It appears that the worms were selective in terms of
particle size ingested. Little else than sand could be seen on micro¬
scopic examination of the feces or gut contents.
Feeding experiments. Transit times for sand from the habitat and
substitute food substrates were investigated as follows. Sand from the
habitat was sifted to obtain the size fractions acceptable to the worms.
Artificial sands were prepared by grinding colored glass to the same
particle size. For some experiments the ground glass was coated as
follows. The glass was placed in running sea water so that a natural
film of material could be aquired or specific substrates were adsorbed.
Bovine Serum Albumin, soluble starch, and vegetable oil (Wesson) were
added to ground glass samples at a concentration of 100 ug/ml of ground
glass. The oil was dissolved in petroleum ether; the protein and car-
bohydrate were dissolved in distilled water. All glass particles with
artificial substrates were dried to constant weight either by heating
to 100°C or at room temperature. Analyses of these artificial sands
revealed that 90 of the protein, 40% of the starch, and 100% of the
lipid remained adsorbed after washing with Instant Ocean. Freshly
collected worms were placed on a test substratum in a Petri dish con¬
taining sea water or Instant Ocean maintained at 15°0. Sea water was
used only with sieved sand from the habitat. Habitat sand was mixed
with ground glass coated with a natural film to permit identification
of this natural test substrate.
Feeding in Ophelia assimilis
Anne Billingsley 6
The normal feeding behavior of worms placed on labelled sand from
the habitat was as follows. After an interval ranging from one half hour
to five hours the worms began to feed. Feeding was readily detected as
the worms everted their proboscides and ingestion could be observed.
Defecation started at the same time and continued as long as the worms
continued to feed. Transit times were measured as the interval between
the start of defecation and the first appearance of color-labelled
substratum in the feces. No defecation occurred if animal were placed
in containers lacking an ingestible substrate.
Animals placed on uncoated ground glass fed for only short intervals
with accompanying short intervals of defecation. Therefore, the transit
time as measured was considerably longer. Transit times of worms placed
on ground glass coated with protein, starch, or lipid approached that of
the worms on the natural substratum. However, feeding was somewhat less
continuous. Table 1 presents the measure and transit times on different
substrates.
Assimilation e
ciency. Table 2 presents the results of chemical
analyses of the sand from the habitat and the feces obtained from the
worm. It is observed that the worms take up about 162 ug carbon per
ml wet sand, or approximately 67% of total organic matter available.
The protein uptake of the sand by the worms was determined to be approximately
152 ug protein/ml sand, indicating a 74% utilization of the protein avail-
able. Fecal samples exhibited a 40% uptake of the polysaccharide car-
bohydrate present in the sand. The lipid content of the sand was
Feeding in Ophelia assimilis
Anne Billingsley 7
xtremely small in amount. No lipid was detected in the fecal material.
DISCUSSION
Microscopic examinations of feeding substrate, gut contents, and
fecal material of Ophelia assimilis indicate that this worm derives most
of its nutrition from organic material adsorbed to ingested sand grains.
Sand grains taken from the guts of freshly collected animals are free
from organic detritus, plankton, or small animal and plant material.
Similarly, defecated sand lacks organic detritus and contains surviving
flagellates and undamaged diatoms which have passed unaltered through the
gut.
Results of organic carbon determinations of sand from the worm's
natural habitat indicate that the sand has relatively low levels of
organic carbon, 270 ug/ml. The worms, however, extract 60-67% of this
organic material. This amount appears to be sufficient to meet their
nutritional needs.
The food substrate consists mostly of adsorbed protein, which is
present in quantities six times greater than the combined polysaccharide
carbohydrate and lipid. The worms are able to extract and utilize 74%5
of this available protein, taking up about 152ug per ml of the sand
that they ingest. The worms assimilate only 40% of the carbohydrate. Lipid
levels are very low. However, the worms may be extremely efficient at
Feeding in Ophelia assimilis
Anne Billingsley 8
extracting lipids, as no trace of lipid material can be detected in the
feces. Protein appears to be the major nutrient in the diet.
O. assimilis appears to be somewhat selective in feeding. Ground
glass lacking either a naturally developed film of organic material or
one of the test substrate resulted in a much lengthened transit time
primarily because it was not readily eaten. The animals stopped taking
in this nutrient-free material after brief periods of ingestion. Not
only do these animals appear to be selective with respect to nutrient
content but they are selective with respect to particle size as well.
Finally, the process of defecation appears to be closely tied to the
process of eating. Defecation was observed to occur only during feeding.
Further work is planned on the nutrition of these animals in relation
to their metabolism and energy budget.
SUMIARY
1) Ophel:
a assimilis is a sand-feeder deriving a large part of its
nutritional requirements from organic material adsorbed to sand
ains, and seemin
gly little else.
2) The worms select for particle size of sand grains when feeding, and
appear to distinguish and select sand grains containing adsorbed
organic material.
Feeding in Ophelia assin
Anne Billingsley 9
milis
3) O. assimilis lives on relatively clean sand with low organic carbon
levels.
4) The food substrate contains proteins, carbohydrates, and lipids, with
protein constituting the bulk of the organic material, and probably
providing the most important nutritional contribution.
5) Transit time for normal substrate is about 40 minutes, with rate
determinations varying as nutritional constitution of the substrate
is varied.
rate lacking adsorbed
6) The worms do not feed readily on a subs
nutrients, implying substrate selectivity.
7) Defecation is observed only during feeding.
ACKNOWLEDGEMENT
I wish to express my gratitude to Dr. Isabella Abbott for her help
and guidence in this project. I would also like to extend special thanks
to Dr. John Phillips for his invaluble and kind help in this research and
paper, and to faculty members Charles Baxter and Robin Burnett for making
life truly enjoyable.
REFERENCE
Dubois, M., K. A. Giles, J. K. Hamilton, P. A. Rebers, and F. Smith.
1956. Colorimetric method for determination of sugars and related
nalyt. Chem. 28: 350-356.
substances. An
Fox, D. L., S. C. Crane, and B. H. McConnaughey. 1948. A biochemical
study of the marine annelid worm Thoracophelia mucronata, its
food, biochromes, and carotenoid metabolism. J. Mar. Res. 7:
567-585.
Hartman, O. 1969. Atlas of the Sedentariate Polychaetous Annelids
from California. Allen Hancock Foundation, Los Angeles, 82opp.
Lowry, O. H., N. J. Rosebrough, A. L. Farr, and R. V. Randall. 1951.
J. Biol. Chem. 1
93: 265.
McConnaughey, B. H. and D. L. Fox. 1949. The anatomy and biology of
the marine polychaete Thoracophelia mucronata (Treadwell) Opheli-
319-5
idae. Univ. Calif. Publ. Zool. 17
Somogvi, M. 1934. The solubility and preparation of phosphorous and
nitrogen free glycogen. J. Biol. Chem. 104: 245-253.
Strickland, J. D. H. and T. R. Parsons. 1965. A Practical Handbook
of Seawater Analysis. Fisheries Research Board of Canada, Ottawa,
205 pp.
Wilson, D. P. 1971. The influence of the nature of the substratum
on the metamorphosis of the larvae of marine animals, especially
the larvae of Ophelia bicornis Savigny. Annls. Inst. Oceanogr.
27; 49-156.
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