FOOD OF THE SEA-URCHIN 



51 



SESSIONAL PAPER No. 22a 



it contains is formed into little masses — the mucinous secretion of the digestive tract 

 holding the grains too;ether. It is usual to find both of these foods in the alimentary 

 canal of our urchins, although one of them may be so abundant that the quantity of the 

 other is insignificant. As stated, when the urchins live in proximity to the large sea- 

 weeds, it is usual to find seaweed almost exclusively in theii intestines. It is not uncom- 

 mon, however, to find a little surface sand, and in a few cases this may form a considerable 

 part of the total content. Thus from one locality where seaweed was abundant, forty- 

 five urchins were taken and examined. In twenty of these there was nothing but sea- 

 w^eed ; in twenty-two others there was over 95 per cent of seaweed and less than five 

 per cent of surface sand. In the remaining three the percentage of surface sand was 

 somewhat larger. Where the large seaweeds are not abundant, yet not scarce, the 

 urchins usually had about equal quantities of seaweed and surface sand in their diges- 

 tive tracts. Sometimes, however, urchins were found with practically all seaweed or 

 all surface sand in their intestines. Even in cases where the urchins were some distance 

 from the large seaweed, one was occasionally found which had eaten a considerable 

 amount of seaweed. Such seaweed is, I think, carried to the urchins by the tides after 

 the waves have torn it from the rocks. In only a few cases was seaweed observed 

 in the intestines of the urchins which had been dredged in the deeper waters of the 

 bay. In their case, as in the case of urchins living on rocks devoid of seaweed, the 

 digestive tract contained chiefly the globular masses of surface sand. Thus there is no 

 doubt that the sea-urchin is, in chief, a vegetarian, although it does eat carrion at every 

 opportunity. 



These observations agree with what is known concerning the food of sea-urchins 

 on the British coast. Sea-urchins have long been known to eat seaweed, for in 1838 

 Sharpey ^ observed the two kinds of food, but considered the surface sand merely as the 

 excrements. He says ' The Echini (sea-urchins) are generally believed to feed on 

 moUusca and Crustacea, and in corroboration of thisj Tiedemann states that he has 

 found in the Echinus sexatilis small univalve and bivalve shells entire among the 

 excrements, besides fragments of larger ones. Blainville, on the other hand, could 

 never find anything else than sand in the alimentary canal, and he remarks that the 

 general opinion as to the carnivorous habits of the sea-urchin is probably more of an 

 inference from the structure of the teeth and jaws than the results of observations ; he, 

 however, adds that M. Bosc had witnessed an echinus in the act of seizing and devour- 

 ing a small crustaceous animal. In the intestine of the E. esculentus we have usually 

 found numerous small portions of seaweed, for the most part encrusted with Flustra. 

 The excrements, which are in the form of small round pellets about the size of pepper- 

 corns, consist chiefly of sandy matter with fragments of shells, but it would be difficult 

 to say whether these are the remains of digested mollusca or merely a portion of the 

 usual testaceous debris so abundant in sand and mud.' In 1877, F. H. Butler ^ wrote, 

 ' The food of the Echinidea consists either of seaweed and small shell-fish and crustaceans, 

 which are conveyed to the mouth by the pedicels, or, as in the case of the edentulous 

 forms, of sand and earth containing nutritive materials.' In 1878, Schmidt^ wrote, 

 ' They are exceedingly inactive, and appear to feed only on the seaweeds and tangs and 

 the animals found on them.' Prof. MacBride, of McGill University, I may add, informed 

 me that my observations agree with what he has observed on the British coast. 



In the case of the urchins found on the North American coast, no one, so far as I 

 could find, has published a detailed account of their food, or has even observed their 

 two kinds of food. In 1867 Sir William Dawson^ published an account of the food 

 of our urchins. His specimens were obtained at Tadoussac, Que., but must have been 

 from a locality remote from the large seavreeds for he found nothing but the surface 

 sand. He writes : ' I found the intestine full of small round pellets, which proved to 

 be made up of the minute confervoid sea- weeds that grow on submerged rocks, mixed 

 with many diatoms and remains of small sponges. It would thus appear that the cur- 

 ious apparatus of jaws and teeth possessed by this creature is used in a kind of brows- 

 ing or grazing process, by which it scrapes from the submarine rocks the more minute 

 seaweeds which cling to them, and forms these into solid balls, which are swallowed, 

 and in this state passed through the intestinal canal, where they may be found in all 



stages of digestion Though the sea-urchin is thus a vegetarian, yet near the fish- 



22a— 4J 



