2l6 BULLETIN OF THE BUREAU OF FISHERIES. 



The European lobster is commonly infested with a small colorless worm, Histriob- 

 della homari, of remarkable habits and doubtful relationship. Discovered in 1853 by 

 Van Beneden on this lobster's eggs at Ostend, it was regarded as a larval serpulid, but 

 later {108) shown by him to be an adult and placed among .the leeches. An account of 

 its anatomy was given by Foettinger (108) in 1 884, but for the most exact anatomical 

 analysis of this curious semiparasite or commensal we are indebted to Shearer (324.), 

 whose work has but recently appeared. He found that it not only Uved among the eggs 

 of the berried lobster, but took up its abode in the branchial chamber and on the gills of 

 both sexes also, passing readily back and forth when its host was a female in berry. It 

 crawls slowly, but is more active among the lobster's eggs, to which it attaches its own 

 ova freely, as well as to the carapace side of the branchial chamber. It is very sensitive to 

 changes in the sea water, and its selection of such lodgings seems to indicate clearly the 

 need of an abundant supply of oxygen. Development is direct, there being no larval 

 stage, and little is known of its distribution or the means by which this is effected. 

 Though possessing toothed jaws, and though seen to bite one another, these parasites 

 are not known to molest either the gills or eggs of their host, and since they often devour 

 diatoms in quantity they may be the lobster's bosom friend rather than its enemy. 

 So far as known at present, Histriohdella is not attached to the American lobster. 



But although parasites are rare , the Inhster is encumbered with a great varietyo f 

 messmates. whi rVi atf-prh thpmgplvpg tn the external shell. "Whenever tb p ^pHctprk 

 confined in inclosures. or compelled for any reason to lead a sluggish life, the common 

 barnacle fixes itself to the arched carapace and begins to secrete its tent-like ^^ cj-.tpverin^ 

 as s ecurely as it might upon a stone; mussels of various kinds insinuate themselves in con - 

 venient angles of the shell and joints, and small tunicates sometimes become attache d 

 firmly to the underside of the shell between the legs. Tube-forming anne^ds. lace-lik e 

 bryozo a, form incrustations in various parts, and red, brown, and green algae often 

 "aec orate the antennae and carapace with long streamers which are waved with eve ry 

 movement of the animal. At each molt the lobster of course frees" itself complet ely 

 from these troublesome companions . (For fuller account of parasites and messmates 

 see J49, p. 122-124.) 



When young lobsters are hatched and reared in confinement they are apt to be 

 troubled with a variety of parasitic fungi and algae, including many species of diatoms, as 

 well as stalked protozoans. Young lobsters captured at sea seem to be peculiarly free from 

 foreign matters of every kind, but when the young of almost any crustacean are confined 

 they are liable to become clogged with solid organic and inorganic particles of many 

 kinds, including living bacteria, spores of fungi, and diatoms. The hairs which garnish 

 the body and appendages of crustacean larvae serve to gather up and hold particles 

 from the water, so that one of the first considerations in the artificial rearing of these 

 animals is to give them as clean a water supply as possible. Old lobsters, in which the 

 molting periods have become very infrequent, are the worst sufferers from enemies of this 

 kind, but the physiological condition of the animal is a most important consideration. 



