236 THE FISHERIES OF THE UNITED STATES. 



bay Long I.slaud, than anywhere else. Mr. Edward TJdall told me tbat the crab was the greatest of all enemies fx> 

 oysters on the Oak Island beds. They eat t^ie small oysters, np to the size of a quarter dollar, chewing them all to 

 bits. These are on the artificial beds, for they do not seem to trouble the natural growth. But attracted by broken 

 oysters, when the jilanter is working, they come in crowds to that point. Mr. Udall stated that once he put down 

 500 bushels of seed brought from Brookhaven, and that it was utterly destroyed by these crabs within a week, and 

 while he was still planting. He could see the crabs, and they numbered one to every fifty oysters. It is well 

 known that in Europe the crabs are very destructive to planted beds, and it is quite possible that many mysterious 

 losses may be charged to these rapacious and insidious robbers. By the way, Aldrovandus, and other of the 

 naturalists of the Middle Ages, entertained a singular notion relative to the crab and the oyster. They state that 

 the crab, in order to obtain the animal of the oyster, without danger to their own claws, watch their opportunity 

 when the shell is open to advance without noise and cast a pebble between their shells, to prevent their closing, 

 and then extract the animal in safety. "What craft!" exclaims the credulous author, "in animals that are 

 destitute of reason and voice." 



The oyster-crabs. — In respect to the little crab, which becomes red in the cooked oyster, but is greenish brown 

 in life, opinion is divided as to whether its in'esence is of any harm to the oyster whose shells give it shelter ; but 

 the probability is that it is not. Its scientific name is Pinnotheres ostreum, and its history briefly as follows, so far 

 as concerns the present inquiry : 



The little red oyster-crab seems to be a parasite. He slips in and out of the oyster almost at pleasure, and 

 enjoys a portion of all the good things the oyster feeds upon. We are told that a careful examination shows that 

 they are almost invariably females and full of eggs. The nudes are so exceedingly rare that it is a matter of 

 astonishment how the propagation of the species is efiected and maintained. These crabs were regarded as 

 luxuries by George Washington. 



The oyster-crab as messmate and purveyor. — It is many years, writes Mr. John A. Ryder, since Mr. 

 Say named the little oyster-crab of our coasts Pinnotheres ostreum, and its habits in relation to the oyster seem 

 to have excited but little interest, especially in foreign waters. Professor Verrill, in his report to the United 

 States Fish Commission, observes that it is the female which lives in the oyster, and that the male, which is smaller 

 and quite unlike the female, is rarely if ever seen to occur, but that it has been seen by him swimming at the 

 surface of the water in the middle of Vineyard Sound. His statement that it occurs wherever oysters occur, I 

 cannot agree with, since out of many hundreds of St. Jerome oysters which 1 saw opened, I never saw a specimen 

 of Pinnotheres; they may occur, but rarely. This little crab has quite a number of allies which inhabit various 

 living mollusks, holothurians, etc., of which admirable accounts are given by Van Beneden, in his work on animal 

 parasites and messmates. 



There can be no doubt that the oyster-crab is a true messmate, and it is highly probable that the presence of 

 these animals in the oyster is rather to be regarded as advantageous than otherwise. The animal lives in the gill 

 cavity of the oyster, and, as will be seen from the following observations, may be the means of indirectly sup]ilying 

 its host with a part of its food. During a reconuoitering trip down the Chesapeake on the yacht Lookout, in the 

 first week of July last, in dredging, some oysters were hauled uj) which contained Pinnotheres. In the case which 

 1 am about to describe, the included crab was a female, with the curiously expanded abdomen folded forward under 

 the thorax and partially covering a huge mass of brownish eggs. Upon examining these eggs, what was my 

 astonishment to find that they afforded attachment to a great number of compound colonies of the singularbell 

 animalcule, Zodihamninm arhusculum. Upon further examination, it was found tliat the legs and back of the animal 

 also afibrded points of attachment for similar colonies, and that here and there, where some of the individuals of' a 

 colony of Zoiithamnium had been sei)arated from their stalks, numerous minute rod-like vibriones had aflixed 

 themselves by one end. In this way it hajjpens that there is a (luadruple commensalism established, since we have 

 the vibriones fixed and probably nourished from the stalks of the Zoiithamnium, while the latter is benefited by 

 the stream of water drawn in by the cilia of the oyster, and the last feeds itself and its jirot^g^, the crab, from 

 the same food-bearing current. Possibly the crab inside the shoU catches and swallows food which, in its entire 

 state, could not be taken by the oyster, but in any event the small crumbs which would fall from the mouth and 

 claws of the crab would be carried to the mouth of the oyster, so that nothing is wasted. We must consider the 

 crab, with its forest of bell animalcules, in still another light. Since the animalctdes are well fed in their strange 

 l)osition, it is but natural to suppose that they would propagate rapidly. They mnltii)ly in two ways, viz, by 

 dividing both lengthwise and crosswise, one half of the product being set free, and known swarmers. These cast-off 

 germs of the animalcule colonies are no doubt liurried along in the vortex created by the cilia of the gills and palps, 

 carried to the mouth and swallowed as i)art of the daily allowance of flic food of the oyster. We are ac(!ordingly 

 obliged to look upon the Pinnotheres in this case as a veritable nursery, upon whose body animalcules are continually 

 I)ropagated and set free as part of the food-supply of the oyster, acting as host to the crab. I do not suppose, however, 

 that such a condition will always be found to obtain, and it must also be remembered that myriads of Zi><ithamniuni- 

 colonies were dredged up on alga-, from the bottom in the immediate vicinity. Such an abundance of germs in the 

 water would favor iheir being readily transplanted or fixed to the body of the oyster-crab.* 



* Report ol'T. B. Fergusou, a fi.sh comiuissioni;r of Miuyhiiul, lur issi, i>|i. '2i, 25 



