PLANKTON OF THE GULF OF MAINE 341 



any reader who may desire knowledge of them. 82 The few species of hydroid medusae 

 which do drift out more or less frequently into the open basin are among the most 

 valuable indicators of coast water. Two of the local species of scyphomedusae, 

 which are of similarly neritic habit, are of still greater interest in this connection 

 because of their large size (p. 33). In the following pages the reader will find notes 

 on the occurrence of most of the species which we have found in any number in the 

 deeper parts of the gulf. 



The ctenophores (p. 365) are much more important in the natural economy of 

 the plankton community than either of the groups just mentioned, for they are not 

 only exceedingly abundant at times and locally in the gulf, but they are among the 

 most voracious of pelagic animals (p. 108). Only one species of siphonophore 

 (p. 377) is a regular inhabitant of the Gulf of Maine. 83 



Hydroid medusa 



Only a few of the many species of hydroid medusae assume any numerical 

 importance in the planktonic communities of the open Gulf of Maine outside the outer 

 headlands and islands, except over the offshore banks. 



Melicerturu campanula (Fabricius) 



This boreal neritic species is common on the North American coast from eastern 

 Newfoundland southward to Cape Cod, and it occasionally occurs as far south as 

 Woods Hole, whence Nutting (1901) recorded it once. It is represented in the 

 northeastern Atlantic by a form {M. octocostatum) so closely allied that it may prove 

 identical when the two are compared critically. The European Melicertum is known 

 from Iceland and from many localities around southern Norway, from the Skager- 

 Rak, all around Scotland, and along the northeast coast of Iceland. 84 



The hydroid stage of M. campanula was grown from the egg by Alexander 

 Agassiz (1865) many years ago, hence there can be no question of its neritic nature, 

 while the medusa stage is so large, so easily recognized, and so closely confined to 

 the immediate vicinity of the land that it is one of the most valuable of neritic indi- 

 cators. Hence, its distribution in the gulf deserves more attention than its slight 

 importance in the natural economy of the plankton might suggest. 



The youngest medusae of Melicertum so far recognized were found by Alexander 

 Agassiz in Massachusetts Bay toward the end of spring. Older stages are common 

 all along the western and northern coasts of the gulf in June (Mayer, 1910, p. 208), 

 and the sexually mature adults swarm in harbors and bays from Cape Cod to the 

 Bay of Fundy during the late summer. It has been found plentiful, for example, 

 in Salem Harbor, in Gloucester Harbor, about Nahant, and off Cohasset in Massa- 

 chusetts Bay; equally at the mouth of the Piscataqua River below Portsmouth; 

 in Penobscot Bay, where I have seen processions of these beautiful medusae drift- 

 ing with the tide in late July and early August; at Southwest and Northeast Harbors 



".See also Fewkes, 1888; Mayer, 1910. I have elsewhere (Bigelow, 1914b) listed all the positive records of the pelagic ccelen 

 terates on the New England coast. 



» For lists of the ccalenterates collected during the summers of 1913 and 1914. see Bigelow 1915 , pp. 308 and 316, and 1917 ,p. 302. 

 « Its occurrence is charted by Kramp, 1919, p. 54, chart 5 



