220 BULLETIN OF THE BUREAU OF FISHERIES. 



INVERTEBRATES. 



Invertebrates in great variety and abundance swarm over and in the mussel beds. 

 The ascidians, Molgula, Cynthia, and Amorecium; numerous Bryozoa; sea anemones, 

 Metridium marginatum and Sagarlia lucice; hydroids, Eudendrium and Tubularia; and 

 sponges grow on the mussels themselves, especially where they are attached to wharf 

 piles (fig. 99, opp. p. 127; fig. 206, opp. p. 220). On the beds other species find it advan- 

 tageous to take up a similar position on the mussels. In some localities, as at Sandwich, 

 Mass., barnacles, Balanus sp?, cover the beds so completely as to hide the shellfish. 

 Lamp shells, Anomia glabra, and boat shells, Crepidula jomicata, also have the habit of 

 attaching themselves to the mussels and competing with them for their food supply. 

 The same is true of the little sea anemone, Sagartia lucim, which is very abundant on the 

 Menemsha mussel beds; Worms of various sorts, Nereis, Lepidonotus, and others, 

 burrow beneath and between the mollusks, and on their shells Hydroides dianthus often 

 secretes its limy tubes. 



The ribbed mussel, Modiolus demissus {Modiola plicatula), common clam, Mya 

 arcnaria, hard-shell clam, Venus mercenaria, oyster, Ostrea virginiana, and the scallop, 

 Pecten irradians, are often associated with the mussel, and the periwinkle, Littorina lit- 

 torea, is nearly always present on the exposed beds in great numbers, especially if eel- 

 grass or algffi is present in abundance. Crabs, Carcinus, Cancer, Libinia, and Panopeus, 

 hermit crabs, Bupagurus longicarpus, and the king crab, Limulus polyphemus, run 

 about over the beds in the shallow, protected estuaries, while in the mantle cavity of 

 the mussel a little crab, Pinnotheres maculatum, finds its abode. Some authorities say 

 the relation between the two species is symbiotic, while others claim it is parasitic, the 

 crab occupying this position to collect the food particles swept in by the ciliarv currents 



of the mollusk. 



PARASITES. 



Polydora ciliata. 



Parasites in the mussel are apparently few in number, only one having been 

 described previously by Lebour (1907), who found a boring annelid, Polydora ciliata, 

 which burrows through the shell, making a hole about the size of a pin. It causes 

 pearly excrescences to grow over the internal surface of the shell which prevents mus- 

 cular development and oftentimes almost destroys the posterior adductor muscle. It 

 furthermore often interferes with the production of the genital products wherever the 

 calcareous ridges press against the mantle. This results in giving the shellfish an un- 

 sightly appearance, which renders it unfit for market. 



Haplosporidium mytilovum, n. sp. 



A new species of sporozoan parasite was recently discovered while the author was 

 studying the maturation of the Mytilus egg. This protozoan occurs in the egg, and its 

 presence there gives rise to a phenomenon suggesting the formation of a chromatin 

 vesicle which for a long time the author took to be a normal process in the development 

 of the egg. The peculiar condition was observed by several prominent zoologists who 

 offered different explanations for its presence. It was finally identified for the author 

 through the kindness of Dr. Gary N. Calkins, of Columbia University, as a probably 

 new species of the genus Haplosooridium. In its vegetative state it is amceboid in 



