208 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Aii oyster which has not been injured by rough treatment has the edges of the 
shell extremely thin and so fragile that they can be broken down with a camel’s hair 
brush. The lower shell is particularly fragile near the edge. It will be noticed, 
however, that the valves frequently do not come together at all at the extreme edge, 
and the real line of contact, the biting edge, is one-fourth inch or more further back. 
The chipping of the margin of the shell by the star- fish is merely accidental, and avails 
nothing in getting at the soft parts of the oyster. I have carefully examined a large 
number of shells of oysters known to have been devoured by star-fish, and, though 
they appear to be badly chipped, the biting edge is never broken, and the shells have 
always been found to be water tight. If such a shell, recently opened by the star, be 
filled with water, and the valves held between the thumb and the finger, the water 
will not leak out even though the shell be violently shaken. 
In mussels which have been opened by the star-fish there is no trace of any 
chipping at all. The reason is plain : the valves of the shell come together firmly at 
the very edge; there is no delicate fringe at the margin. The same is, of course, true 
of the quahog. Nevertheless, the small quahog and mussel are readily opened by 
the star-fish. It follows, therefore, that if the star gains entrance to the soft oyster 
by chipping off the edge of the shell, a different process must be adopted in entering 
a mussel or quahog, to say nothing of the snails which it also devours. 
The credit of solving the problem — How do the star-fish open oysters'? — is due to 
Dr. Paulus Schiemenz of Hanover, Germany, who carried on his investigations at the 
famous zoological station at Naples. The problem Avas suggested to him by Collins’s 
report of the enormous injury done to the oyster-beds by the star fish in Long Island 
Sound. The process is briefly as follows: The star-fish so covers his victim that the 
suckers on the under side of the arms are distributed, part to one valve, part to the 
other, and the remainder frequently to some surrounding object. (In the case of the 
snails the suckers are attached to the operculum and to the shell.) The suckers are 
very numerous and stick fast, and a tendency to straighten the arms results in a 
constant pull on the shells in opposite directions, which, if strong enough, would open 
the shells. It is true that a star-fish is not strong enough to open an oyster or quahog 
immediately in this manner, but it can and does fatigue its prey. The constant, 
steady pull in opposite directions soon fatigues the muscle which holds the shell 
together, and the oyster or clam presently gapes open. The oyster can overcome a 
strong pull for a short time, but not a \A T eaker pull for a long time. The same prin- 
ciple is well illustrated in the case of the periwinkle or couch. If a string be tied 
around the “foot” so as to give a good hold on the animal, a strong man can not pull 
the mollusk out of its shell, belt if it be suspended by this string it can not sustain 
for a long time even its own weight. On the same principle a man aa 7 1io can hold at 
arm’s length a weight of 20 pounds can not hold his empty hand in this position for 
10 minutes. Schiemenz showed by experiment that the star-fish could exert a pull of 
o\ 7 er 1,200 grams, and that a pull of 900 grams is sufficient for opening a good-sized 
quahog if allowed to act for 30 minutes. 
Often more than one star takes part in opening an oyster, and when opened 
other stars often enter into the feast. It is the young oysters that are in greatest 
danger from the stars, and the danger decreases as the oysters grow larger. Oysters 
of marketable size, that is, three or four years old, are comparathmly unmolested. Of 
course the larger stars can open the larger oysters, but fortunately the larger ones are 
more easily caught in the “ mops” and thus more easily kept off the beds. It has not 
been ascertained how large an oyster can be opened by a star-fish. 
