582 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



The objects to which these pentacrinoids attach themselves, or at least upon 

 which they will survive after attachment, are circumscribed by certain economic 

 considerations (1) a free circulation of pure well aerated water must be assured, 

 and (2) there must be an adequate food supply. 



Thus in shallow water mobile arborescent organisms, such as hydroids and 

 bryozoans and seaweeds of all sorts, particularly laminariae, are usually chosen. 

 In an aquarium the larvae will attach to practically anything, even the glass walls, 

 but in the sea the young of littoral types are only very exceptionally found on 

 dead objects. 



Lo Bianco has noticed that in the echinoderm tank at the Stazione Zoologica 

 at Naples the pentacrinoids of Antedon mediterranea, in different stages up to 

 about 7 mm. in length, are almost always found attached to the walls of the 

 aquarium or to old branches of gorgonians and antipatharians ; these do not 

 develop further, possibly, he suggests, through lack of nutriment. 



In the sea he found pentacrinoids of the same species in all stages up to the 

 fully grown ready to discard the stem on the firmer algse (Sargassum, Halymeda, 

 and C'odium) and on different branched organisms dredged where the crinoid lives. 



In deeper water, where the aeration is more uniform and the food supply 

 less subject to local fluctuations, while the arborescent organisms, particularly the 

 hydroids, are still the usual objects of attachment, the pentacrinoids are often 

 found on bivalve molluscs, barnacles, and other organisms (there is one record of 

 a pentacrinoid on the carapace of a crab), and on foraminifera, and the spicules 

 and skeletons of dead sponges and other animals. 



So far as I am aware no pentacrinoids have ever been found attached to 

 stones. This, however, is probably due to the fact that in water sufficiently pure 

 and with a sufficiently high food content for young crinoids the ocean bottom is 

 more or less completely covered with a growth of other organisms. 



The pentacrinoids of the following species are found attached to the cirri of 

 more or less fully grown specimens: 



Comissia littoralis. Leptometra phalangium. 



Comissia hartmeyeri. *Helwmetra glacialis. 



Comactinia meridionalis. * H athrometra prolixa. 



Comanthus wahlbergii. Isometra vivipara. 



In the two species marked with an asterisk (*) the pentacrinoids are also 

 found attached to other objects, and their attachment to the cirri of the fully 

 grown appears to be more or less a matter of chance ; that is to say, they will attach 

 themselves to any suitable object, whether it be the cirrus of an adult or any other 

 support. 



But in the case of the other six attachment to the cirri of larger animals 

 of the same species appears to be the invariable rule, and in these they are attached 

 not to all of the cirri or to any of the cirri indiscriminately, but always to certain 

 of the longest peripheral cirri which are not used for gripping the object to which 

 the foster parent is fixed, but are raised upward toward or between the arms 

 so that the crowns of the pentacrinoids appear on the ventral surface standing up 

 between and above the pinnules. 



