330 



this temperature does not act as a critical factor in the control of breeding, as it does 

 at Beaufort. It appears therefore that the temperature of 14° is critical only when 

 associated with a great annual variation in temperature, and the relatively small 

 annual variation in temperature in San Francisco Bay may account for the lack of 

 a definite breeding season of Limnoria in this region. 



It is to be noted that Limnoria has been found as far north as Kodiak Island 

 on the Pacific Coast and well within the arctic circle on the Scandinavian Coast. 

 The temperature at these localities must always be less than 14° C. 



Commensals and Parasites of Limnoria 



The organisms which are attached to the body of Limnoria are related to it 

 either as commensals or as parasites. The former consist of sessile Protozoa and the 

 latter of a species of nematode and an unidentified organism, possibly a trematode. 



The sessile Protozoa attached to the exterior of Limnoria are often very numerous. 

 The telson, the ventral portions of the epimera, the basal joints of the legs, the mouth 

 parts, the pleopods, the bases of the antennae, and the lamellae of the brood pouch 

 serve as points of attachment for great numbers of these organisms. They apparently 

 do not penetrate below the epidermis into the body of their host, but are merely 

 attached to it by a sticky secretion at their bases, and for this reason we have indicated 

 them as commensals. 



The most commonly found include the following: Follicidina, Spirochona, Epi- 

 stylis, Opercularia and Cothurnia. Follicidina sp. is found most frequently on the 

 telson, but they also occur on the posterior segments of the abdomen. These organ- 

 isms are frequently so numerous as entirely to cover the telson. The dark green tubes 

 in which Follicidina live are very characteristic. They have been found on about 

 80% of the individuals examined. 



Of the other commensals, Spirochona and Epistylis are probably the most nu- 

 merous. Spirocli07ia is frequently attached to the pleopods and Epistylis to the head 

 and the epimera. Suctorians have been mentioned by Hoek (1893) as occurring on 

 Limnoria but we have not seen them. 



The parasitic nematodes are found in two places on the body of Limnoria. They 

 are found loosely attached under the fold of chitin between the first segment and the 

 head. There is a considerable space here and it is practically always invaded by these 

 organisms in great numbers. As their presence here does not seem to be detrimental 

 to the host they may be included with the commensals; they occur, however, in the 

 brood-cavity containing the eggs and the liquid which bathes the latter, and their 

 presence here should be regarded as parasitic, since they must obtain their nourish- 

 ment from the fluid of the brood-cavity. 



The other organism injurious to Limnoria has not been identified. We have only 

 found it when encysted; no active animals have been seen. The cyst is approximately 

 round and occurs near the base of the inner ramus of the pleopods. It presents a 

 granular appearance but no definite structures have been seen. It has been suggested 

 by Hoek that it is a trematode. 



To summarize, we may say that there are numerous protozoa living as commensals 

 on the body of Limnoria. There is also a nematode occurring in the brood-cavity 

 and attached under a fold of chitin back of the head. There is a parasitic organism, 

 possibly a trematode, often found encysted near the bases of the pleopods. 



