PELAGIC ANIMAL LIFE 



577 



The larval Actiniae are biologically of great interest, especially Actiniaria. 

 AracJinactis albida, first described by Michael Sars (Fig. 412). The north- 

 eastern corner of the Atlantic is its main area of distribution, principally 

 between the Hebrides and the Faroe Islands, but at certain seasons it is 

 carried into the North Sea and the Skagerrack, and to the west coast of 

 Norway, where Sars found it (see Fig. 480). 



A description of the larvae peculiar to the different groups would lead 

 us too far, but in order to prepare the reader for the next chapter 

 some of the forms have been mentioned. 



r 



The Worms are comparatively rare among the pelagic forms. Of Vermes, 

 the lowest worms (platyhelminthes) the pelagic Nemertines are of 

 interest. Nearly all Nemertines live along the 

 bottom, but a pelagic genus {Pelagonemertes) was 

 described by Moseley in the " Challenger" Reports. 

 Subsequently several species have been described, 

 all represented by isolated specimens. These re- 

 markable forms are red or orange coloured, and 

 their digestive tract is extremely ramified. Accord- 

 ing to Brinkmann, who is examining our material, 

 most of the previously known species, as well as 

 some new species, have been taken during our 

 Atlantic cruise, and prove that several species 

 hitherto regarded as distinct are really identical : 

 thus Nectoneinertes grimaldi^ N. lobata, and 

 N . pelagica are all identical with N. mirabilis. The 

 genus Nectonemertes with N. mirabilis, and also 

 the genus Hyalonemertes with H. atlantica, were 

 established by Verrill. The two forms (see Fig. 

 413) differ, as shown by later investigations, only 

 in one single character, N. mirabilis having two 

 long appendages on the head, which are lacking 

 in H. atlantica. The abundant material collected 

 by the " Michael Sars" has enabled Brinkmann to 

 show that all the individuals of N'. mirabilis are 

 males, while all the individuals of H. atlantica are 



females, and he concludes that both belong to the same species, the 

 difference between them being only a sexual one. 



Very interesting were some gigantic specimens belonging to this 

 group secured during the cruise. One form, Dinonemertes investigatoris 

 (see Fig. 414), was 20.5 cm. long, and when living was of a bright red tint 

 and nearly transparent, all the ramifications of the digestive tract being 

 plainly visible. As we shall see when reviewing the captures of the 

 " Michael Sars," all these Nemertines are deep-sea forms with a very 

 characteristic vertical distribution. Several of the species are very widely 

 distributed, Nectonemertes mirabilis, for instance, being known from 

 Davis Straits, from the Pacific off California, and all through the Atlantic ; 

 Dinonemertes investigatoris is known from the Atlantic as well as from 

 the Indian Ocean. 



The most abundant group of pelagic worms as regards number of 



2 P 



Fig. 413. 



Nectotieme rtes mirabilis, 

 Verrill. Slightly enlarged. 

 a, male ; b, female. 



