62 SURVEY OF INVERTEBRATES 



sumption may be dependent upon two different processes 

 which thus far are affected l)y the same treatment and 

 conceivably some treatment might be found where either 

 could be changed independently of the other." 



Other special functions of the coelenterates do not de- 

 pend on the presence of oxygen. Harvey (1926) and 

 Harvey and Korr (1938) demonstrated that the lumi- 

 nescence of ctenophores and of the medusa Pelagia noc- 

 tiluca does not require molecular oxygen in the surround- 

 ings. 



III. WORMS AND WORM-LIKE ORGANISMS' 



1. NON-PARASITIC SPECIES 



A. Occurrence in anaerobic habitats. There is no defi- 

 nite evidence that any non-parasitic worms or worm-like 

 organisms are adapted to a permanently anaerobic life, 

 but many are known that live temporarily in the absence 

 of oxygen. 



( a ) F r e s h - w a t e r forms. Lauterborn ( 1916) 

 describes many gastrotricha and rotifers, some oligo- 

 chaetes, nematodes and flatworms as members of the sap- 

 ropelic fauna (see Appendix, Table 1). It should be 

 remembered, however, that Wetzel (1928) has demon- 

 strated that only the mud itself and the water in imme- 

 diate contact with it are truly oxygen-free in typical sap- 

 ropelic habitats. To what extent the animals are con- 

 fined to these zones has not yet been sufficiently estab- 

 lished. 



Many of these organisms are much larger than the 

 anaerobic sapropelic protozoa. This is an important 

 point to keep in mind, for it is conceivable that larger 

 animals, being able to wander over farther distances than 

 smaller ones, may from time to time reach layers con- 

 taining molecular oxygen and thus they will only tempo- 



1 Under "worm-like organisms" we include animals like gastro- 

 tricha, rotifers and chaetosnatha. 



