2i6 
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 1884, 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 lived 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, Histriobdella is not attached to the American lobster. 
But although parasites are rare, the lobster is encumbered with a great variety of 
messmates, which attach themselves to the external shell. Whenever the lobster is 
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 covering 
as securely 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 attached 
firmly to the underside of the shell between the legs. Tube-forming annelids, lace-like 
bryozoa, form incrustations in various parts, and red, brown, and green algae often 
decorate the antennae and carapace with long streamers which are waved with every 
movement of the animal. At each molt the lobster of course frees itself completely 
from these troublesome companions. (For fuller account of parasites and messmates 
see 149, 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. 
