122 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
flsli, some of Avliich, like the menhaden, 1 roam about in vast schools, straining the 
water as effectively as the towing net. During this period the lobster measures 
from one-third to two-thirds of an inch in length, and is not only helpless in the hands 
of its animate enemies, but is subject to a vast amount of indiscriminate destruction 
from the forces of inanimate nature. (For the further consideration of this subject 
see pp. 187-189.) 
PARASITES, MESSMATES, AND DISEASES OF THE LOBSTER. 
One of the two parasites known to infest the lobster is a trematode ( Sticlioco - 
tyle nethropis). This was first described by Cunningham, who found it in the intestine 
of the Norwegian lobster. It has recently been discovered in the American lobster 
by Dr. Nickerson, to whom I am indebted for the following particulars. The larva 
of this singular parasite, which is from 3 to 7 millimeters long, is found sometimes to 
the number of 70 or more embedded in the mucous coat of the intestine about the 
coecum. It is relatively rare, hardly more than 2 per cent of the lobsters which Dr. 
Nickerson examined being infested by it. Its position at the hinder end of the 
alimentary tract seems to argue that it comes in by way of the anus rather than 
through the mouth. Its final host is probably some species of fish which feeds upon 
the lobster, but the adult trematode is unknown. It may prove to be of a different 
species from the larva discovered by Cunningham. 
The only other strict parasite which the lobster is known to possess is the large 
Gregarine (G. gigantea), which was discovered in the intestine of the European lobster 
by Van Beneden. {194) 
In 1853 Van Beneden (69) called attention to a small green worm which he found 
on the eggs of the lobster, and which he supposed was a larva of Serpula. Later, 
in 1858, he concluded that the animal was not a larva, but a fully developed indi- 
vidual, which he called Histriobdella liomari, placing it among the Hirudiuese (69). 
Foettinger, a later student of this form (69), proposes to change its name to Histrio- 
drilus benedeni, and concludes that is is an Enteroccelian, allied to Polygordius. It 
is not a parasite in the strict sense. 
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 convenient angles of the shell and joints, small 
tuuicates sometimes becoming attached firmly to the under side 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. 
1 Regarding tlie menhaden as an enemy of the larval lobster, I have consulted Avitli my friend, 
Professor J. I. Peck, who has made a very careful study of the habits of these remarkable fish. He 
Avrites as follows : “ I have never found lobster larvae! in the stomachs of menhaden, and yet it must be 
remembered that the localities whence my material was nearly all secured were brackish-water inlets. 
Copepods in all stages of growth are abundant and shrimp of the smallest size were common at New 
Bedford, but in the material from Buzzards Bay I have never seen lobster larvae.” He thinks that 
the evidence can not be conclusive until menhaden are examined which have fed both day and night 
in localities which abound in lobsters. 
