ON CERTAIN PARASITES, COMMENSALS, AND DOMICILI- 
AES IN THE PEARL OYSTERS MELEAGBINxE. 
By Eorert E. C. Stearns. 
The presence of nodules or tubercles ou the interior surface of the 
shells or valves of lainellibraucli (bivalve) mollusks is of frequent oc- 
currence. These excrescences are nacreous or otherwise, according to 
the character, in this respect, of the shell in which or upon which they 
occur. They are found alike in fresh-water and marine species. In the 
pond and river mussels (TJnionidce), they are chiefly due to interior 
causes; in marine forms, like the cockles (Cardium), mussels (Mytilus), 
the scallops (Pecten), etc., these formations are generally traceable to ex- 
terior causes. It is often the case that specimens of the large scallop of 
the New England coast (P. tenuicostatus), are so burrowed into by a spe- 
cies of sponge (Cliona sulphured) that nearly the entire inside surface of 
the valves will be roughened with sharp, thickly-set pustulse. 
So, too, with the beautiful pecten of the west coast, P. hastatus, com- 
mon in certain localities in Puget Sound. Fully one-half of the speci- 
mens obtained by the dredge are so defaced by the ravages of a similar 
species of sponge as to be of no value. 
We sometimes meet with these nodulm in the shells of marine gas- 
tropods, notably the Haliotida?, popularly known as Abalones, or ear- 
shells. In all of the marine species in which these nodules occur it 
will usually be found that the substance of the shell has been bored 
into from the outside by either a species of pliolad or lithodomus. 
Neither of these forms are, properly speaking, either parasites or com- 
mensals. 
They are, more definitely, domiciliares, and excavate their burrows, 
not for the purpose of getting at the softer parts of the mollusk upon 
whose shell they have “squatted” in order to use said softer parts as 
food, after the manner of the predaceous Xaticas and Purpuras, but 
solely for the purpose of a residence or domicile. 
The lithodomi, especially, burrow into many species of shells, and the 
pholad, so often found in the heavy shells of old individuals of .the 
Haliotidce, I am inclined to believe as a differentiated and dwarfed va- 
riety of a widely distributed roclc-horer. A related form (Martesia 
cuneiformis Gray) is common on the Atlantic coast of North America, 
and may often be seen in situ in the shells of the common oyster (0. 
virginica). 
The burrows of these shell-boring pholads and lithodomi are at first 
quite small, increasing in size in the same ratio as the Rummer in- 340 
MISCELLANEOUS PAPERS. 
creases in age or in growth. After a while the depth of the boring is 
equal to the thickness of the shell in which it has been made, and the 
occupant of the latter, in order to keep his own shell intact and main- 
tain the integrity of his own domicile, commences depositing layer upon 
layer of nacreous or porcellaneous. matter, as the case may be. In 
keeping pace with the continued encroachments of the domiciliary 
squatter upon the outside, this deposit finally becomes a more or less 
conspicuous protuberance. 
In one of the mother-of-pearl shells which illustrate this paper (Plate 
I, which exhibits, as do all the figures, the inner side of the shell), the 
exterior has been perforated in both directions; that is to say, trans- 
versely, or at right angles to the growth-layers of the shell also between 
the growth-layer8, the first class of perforations leading to the separate 
rounded nodules and the latter to the elongated form. If the reader 
had the shell in his hand, so that he could turn it over and examine 
the exterior perforations, he would at once perceive that the site of each 
of the nodules or tubercles exactly corresponds with the site of an ex- 
terior perforation or burrow. 
In the Ilaliotis shell, the domiciliares are a species of pholad [Penitella 
parva Tryon), and the site of each may be seen on the outside of the 
shell and the corresponding nodosity on the inside. 
Plate I represents an adult abalone or ear-shell, Ilaliotis rvfescens 
Swainson (Mus. No. 74877), a Californian species. The figures 1,2, and 
3 indicate the rounded elevations of nodules caused by Penitella, and 
figures 4, 5, and G show the ends or edges of the pholad shells, the sur- 
face of the ear-shell having been bored through or otherwise removed. 
Sometimes these nodules or tubercles are due to some foreign inor- 
ganic matter, a particle getting in between the mantle of the mollusk 
and the inner surface of its shell. In such cases it is, we may say, at 
once plastered over, and thus fixed upon the surface of the valve. 
Free concretions, i. e., unattached or non-adlierent nodules, are, as is 
well understood, caused by some particle, organic or inorganic, becom- 
ing in some way lodged exclusively in the soft parts of the body of the 
mollusk, and so far away from the surface of the shell as not to admit 
of its being cemented to it. 
No doubt many of the mollusca, both gastropod and lamellibranch, 
contain or are inhabited by true parasites. In certain species of fresh- 
water mussels (Anodonta cygnea of Europe, and Anodonta duviatilis of 
America) a species of water mite (Atax) has been detected, and some- 
times Filaria (thread worms) and other forms occur. 
CRUSTACEAN PARASITES. 
A small species of crab (Pinnotheres), an epicurean no doubt, finds 
a salubrious habitation in the common oyster, but parasites of any con- 
siderable size appear to be rather rare. 
Besides Pinnotheres ostreum Say, the name of the species above referred PEARL OYSTER PARASITES, ETC. 
341 
to, another small crab (Pinnotheres maculatus Say) is sometimes found 
in the common mussel (Mytilvs edulis), and the large scallop (Pecten 
tenuicostatus) before mentioned. It is doubtful, however, whether these 
crabs are really parasites or only commensals, though probably the 
former. 
Before the Zoological Society (London, April 6, 180C), Dr. TI. Wood- 
ward exhibited specimensof animals, commensal or parasitic, in thepearl 
mussels of Australia. Among these was “a specimen of Pinnotheres 
which has been entombed in a cyst of pearl by a living pearl-mussel,’7 
etc. 
He further remarked: u It seems extraordinary and beyond belief 
that the Meleagrina should of all the Conchifera be the one to resent the 
commensalism of the pea-crab, which has been known since the days of 
Cicero, Pliny, Oppian, and Aristotle, to inhabit the shell of the Pinna 
and the oyster, and has-been recorded from Astarte, Pectunculus, and at 
least some half-dozen other bivalves, with whom it appears to live on 
the most friendly terms. 
“ It is the females, however, which constantly reside within the shells 
of the Conchifera, whilst the males are said to avail themselves of favor, 
able opportunities to visit the females in their retirement. 
u Whether or not in this case the unlucky male intruded himself upon 
Meleagrina at an unfavorable period, and, finding no female Pinnotheres, 
penetrated so far beneath the mantle of the pearl-mussel as to be un- 
able to retreat, one thing is quite clear, namely, that the Meleagrina 
entombed the intruder in a cyst of pearl from which the clever pearl- 
button maker alone liberated him.” 
FISH TAEASITES. 
WTe have, however, evidence of the occurrence of fishes of two species 
as parasites in the true pearl oyster, or mother of pearl shell Meleagrina, 
not by the presence of the living fish, or even by dead specimens of 
“ fish in the flesh,” if we may use so convenient a paradox, but by their 
entombed remains in the form of nacreous nodulae or tubercles on the 
shells or valves of the said mollusk. 
At a subsequent meeting of the Zoological Society (June 3, 1886), 
Dr. Gunther exhibited a specimeu of a small fish of the genus Fierasfer 
embedded in a pearl oyster, and said : 
“ The specimen which is represented in the accompanying wood-cutT 
of the natural size has been in my possession for many years. It is an 
old shell of Margarita margaritifera,* in which there is imbedded, be- 
hind the impression of the attractor muscle, a perfect individual of a 
fish belonging to the genus Fierasfer. The fish is covered by a thin layer 
of pearl substance, through which not only the general outlines of the 
body but even the eye and the mouth can be seen. The parasitic habits 
eleagrina margaritifera L. 342 
MISCELLANEOUS PAPERS. 
of Fierasfer are well known, and Putnam describes, iu. tbe 1 Proceedings 
of tlie Boston Society of Natural History,’ Vol. xvi, 1874, p. 344, a spe- 
cies, Fierasjcr dubius, which is found on both coasts of Central America, 
but inhabits holothurians on the Atlantic and pearl oysters on the Pa- 
cific side; and he further mentions, in a foot-note, an example belonging 
to the Museum of Comparative Zoology at Cambridge, in which also a 
Fierasfer has been imbedded in the substance of the shell. In this case, 
as well as in ours, the fish, instead of introducing itself into the cavity 
between the two halves of the mantle, penetrated between the mantle 
and the shell, causing irritation to the mollusk, which the latter resented 
by immediately secreting the substance with which the intruder is now 
covered. It is remarkable to note that the secretion must have taken 
place in a very short time, at any rate before the fish could be destroyed 
by decomposition.” 
Soon after the close of the New Orleans Exposition Prof. F. Ferrari 
Perez and Senor J. G. Aguilera, of the Mexican Geographical Commis- 
sion, visited Washington and remained here for several weeks for the 
purpose of comparing and identifying various natural history material 
with the assistance of the curators in different departments of the Na- 
tional Museum. 
The collections in charge of these gentlemen, so far as molluscan forms 
are considered, were rather meager, though many interesting points 
pertaining to geographical distribution were derived from the examina- 
tion. 
The collection included a hundred or more valves of the common pearl 
oyster of the Pacific coast of Mexico, Meleagrina fimbriata Dkr., of 
which two or three species have been made by as many authors. Upon 
examining these last winter I found a single valve (see Plate II, Fig. C), 
the right half of a rather young individual in which was imbedded, in 
very nearly the same region as in the specimen mentioned by Ur. Gun- 
ther, a small fish of rather a long and slender form, probably of the 
same genus and perhaps the same species as that inclosed in his (Gun- 
ther’s) pearl-oyster valve, and previously described by Putnam, as 
quoted by Gunther. The Mexican collection contained but a single 
specimen of this special character. 
ANOTHER SPECIES OF FISH DETECTED. 
Among the lot, however, were two or three valves, in each of which, 
inclosed in nacreous splendor, was a specimen of a small fish, apparently 
a species of Oligocottus* In each instance the fish had worked its way 
between the interior face or surface of the valve and the mantle towards 
and near to the adductor muscle, as can be seen by examining the shell 
close by the muscular scar. 
The squarish, chunky head of the little intruder, also the somewhat 
* Submitted to Dr. Bean, curator of ichthyology, who, though not ]> 
fiedly refers it to this group. PEARL OYSTER PARASITES, ETC. 
343 
prominent spines of the head, are easily discerned, though covered and 
partially obscured by the coating of nacre. (See Plate III, Fig. D.) 
The singlo specimen containing the inclosed Fierasfer was retained 
by the commission, but one of the others (Plate III, Fig. E) was kindly 
presented to the National Museum. (No. 73934a.) 
I am not aware that the occurrence of Oligocottus in this way has here- 
tofore been observed or made known. 
This determination is not positive. The specimen (73934a) repre- 
sented in Plate III, Fig. E, is not as favorably presented for this pur- 
pose as in the others in the possession of the commission. 
The genus Oligocottus Girard includes certain small fishes inhabiting 
rock pools between tide marks on the Pacific coast of North America. 
The species described, and their distribution as given in Jordan and 
Gilbert’s Synopsis of the Fishes of North America (Bulletin of the U. 
S. National Museum, No. 16), is as follows: 
0. analis Grd., coast of California; abundant in rock pools, from 
Monterey southward to Lower California. 
0. maculosus, Grd., San Luis Obispo to Alaska, exceedingly abun- 
dant northward. 
0, globiceps, Grd., Pacific coast northward to Kodiak, in rock pools; 
rather rare. 
Assuming that Dr. Bean is correct in placing the above in this group, 
it will be observed that whether it belongs to the more southern species 
of the three (0. analis) or otherwise, the geographical disribution is 
evidently considerably extended, as the pearl oysters in which our 
specimens are inclosed came from the Gulf of California, where the 
fishery of these shells is carried on. 
After entering the shell, which of course must be at such time as 
the valves are partially open or gaping, these fishes find no obstruction 
to their course as they push their way towards the interior between the 
mantle and the smooth inner surface of the valves until they approach 
the adductor muscle, and here they find a barrier which most likely 
causes them to expend somewhat greater activity or energy and conse- 
quently in a correspondingly increased degree disturb the serenity if 
not the structural economy of the oyster. 
Having reached thus far, the invader is in the immediate vicinity of—if 
not the seat of intellect, then—the center of sensitiveness. The deposit 
of nacre in such instances must be very rapid, and it is quite possible 
that the unwelcome explorer is not only enshrouded and entombed in 
pearl, but previously drowned in a pearlaceous flood, for it may be rea- 
sonably presumed that the annoyance caused by its presence must be 
exceedingly great, and likely to induce a copious flow of nacreouslymph 
at the point and in the region of greatest irritation. 
It is evident that the deposition and induration are sufficientlv rapid 
to inclose the parasite before decomposition has taken place. 
December 15, 1886. 344 
MISCELLANEOUS PAPERS. 
Plate I. 
(Fig. A.) 
ITaliotis rufescens Swainson (Museum No. 74877), the red-backed car-shell or abalone 
of California and elsewhere, on the west coast of America (somewhat reduced). 
The figures 1, 2, and 3 indicate nodules caused by the burrowing of a pliolad, Feni- 
tellaparva, and 4, 5, and 6 show other nodules, the nacreous coating removed by ac- 
cident or otherwise, exposing the edges of the pholad shells, etc. 
From nature, by W. II. Chandlee. 
(Plate II.) 
Fig. B. 
Eight valve of the pearl-oyster, mother-of-pearl shell Meleagrina fmbriata Dun- 
ker, two-thirds natural size (a West Mexican species) showing rounded and elongated 
tubercles or noduloe caused by perpendicular and inter lamellar perforations of litho- 
(lomi. 
From nature, by W. II. Chandlee. 
Specimen belongs to U. S. Nat. Museum, No. 739346. 
(Fig. C.) 
Eight valve (two-thirds natural size) of Meleagrina fmbriata Dkr., mother-of-pearl 
shell from west coast of Mexico with parasitic fish Fierasfer inclosed in same. 
From nature, by A. Z. Shiudler. 
Specimen belongs to the Mexican Geographical Commission. 
Plate III. 
(Fig. D.) 
Eight valve (two-thirds natural size) of Meleagrina fmbriata Dkr., mother-of-pearl 
shell from west coast of Mexico with parasitic fish Oligocottus sp. inclosed in same. 
From nature, by A. Z. Shindler. 
Specimen belongs to the Mexican Geographical Commissior 
(Fig. E.) 
Left valve (two-thirds natural size) of Meleagrina fimbriata Dkr., from west coast of 
Mexico, with parasitic fish Oligocottus sp. inclosed in same. 
From nature, by W. II. Chandlee. 
Specimen belongs to the U. S. Nat. Museum, No. 73934a. Smithsonian Report, 1886, Part I.—Oyster Parasites. Stearns. 
Plate I. 
Fig. A.—HaUotis rufescens. (Nearly natural size.) Smithsonian Report, 1886, Part I.—Oyster Parasites. Stearns. 
Plate II. 
Fig. B.—Right valve of Meleagrina fimbriata. (J natural size.) 
Fig. C.—Right valve of Meleagrina fimbriata. (f natural size.) Smithsonian Report, 1886, Part I.—Oyster Parasites. Stearns. 
Plate III. 
Fig. D.—Right valve of Meleagrina fimbriata. (f natural size.) 
Fig. E.—Left valve of Meleagrina fimbriata. (f natural size.)