578 



DEPTHS OF THE OCEAN 



individuals is the Sagittidee or Chsetognaths, which, 

 along with copepoda, salpaj, pteropoda, and radiolaria, 

 everywhere constitute the bulk of the small pelagic 

 organisms captured by our fine-meshed tow-nets. They 

 are perfectly transparent, of slender build, and swift of 

 motion. On the head are some bristle-like gripping 

 appliances, and an elastic film-like rim, reminding one 

 of the fin of a fish, runs along the 

 body and the "tail "(see Fig. 41 5). 

 The Sagittidae comprise only 

 a few genera, the most prolific in 

 species being the genus Sagitta, 

 which is represented in all 

 oceans ; some of the species are 

 very widely distributed, such as 

 Sagitta hexaptera, S. serratoden- 

 tata^ S. bipiinctata. In northern 

 waters Krolmia hamata, Sagitta 

 arctica, and Sagitta gigantea are 

 characteristic forms, the last men- 

 tioned having been taken by the 

 "Michael Sars" in deep hauls 

 in the Norwegian Sea, while 

 Sagitta inflata is a form peculiar 

 X I to warm waters. All these 



I I species are perfectly transparent, 



I I but during the Atlantic cruise 



we found specimens of a bright 

 red colour, precisely like that of 

 the pelagic Nemertines, belong- 

 ing to Sagitta niacrocephala and 

 Eukrohnia foivleri; they were 

 very abundant, and occurred, 

 like the Nemertines, only in 

 deep hauls. 



The very numerous families 

 of higher worms, especially the 

 Annelida, contribute very little 

 to the pelagic fauna of the ocean. 

 Among the best known is the genus Tornopteris, which 

 has many beautiful surface forms, some of these (like T. 

 septenti'ionalis) being boreal, some belonging to warm 

 waters. In his narrative of the cruise of the " Valdivia," 

 Chun tells us that nearly every haul from deep water in 

 the Antarctic brought up beautiful specimens of Tomop- 

 teris, as long as the finger, transparent, and with rose- 

 tinted feet (parapodia). Individuals belonging to the 

 genus Tomopteris were taken in several of the deep 

 hauls and also in the surface hauls of the " Michael 

 Sars," but the material has not yet been worked up. 



Fig. 414. 



Dinonemertes investigatoris , 



Laidlaw. Half nat. size. 



d'Orb. {\). (From 

 Hertwig. ) 



