34 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 128 



fication by Dr. Osburn of 21 different species of bryozoans from two 

 faces of a single valve of Pecten islandicus. 



With such a dense population, attachment space is at a premium; 

 consequently almost no sessile animal or colony of animals is with- 

 out its quota of other animals growing upon it. Hydroids commonly 

 have other hydroids, bryozoans, foraminifers, and tunicates, such 

 as Molgula griffithsi and Boltcnia ovijera, growing on them. The 

 asexual form of the syllid worm Autolytus jallax was frequently found 

 with its tube attached longitudinally to the chenille-like stems of the 

 hydroid Lafoeina (possibly maxima Levinsen). The long, straw- 

 colored stems (up to 150 mm. in length) of a species of Tiihidaria 

 were often supported by the mud-tube nests of the amphipod 

 Ericthonius tolli forming a mass surrounding the stems. In one such 

 mass a sipunculid, Golfingia margaritacca, was living in one of the 

 mud tubes, and an annelid, Thelepus cincinnatus, was living in its 

 coarse-sand-encrusted tube twining among the stems of the hydroid. 



Both erect and foliaceous, as well as encrusting, bryozoans are 

 favorite places of attachment for foraminifers, hydroids, other 

 bryozoans, and tunicates. A colony of Eucratea loricata, dredged 

 from 213 feet, had the following animals growing on it: Foramini- 

 fers ; the bryozoans Hincksina nigrans and Costaaia nordenskjoldi; 

 caprellids; a tunicate, Styela rustica macrenteron, that was 6.1 mm. 

 long; and a small clam, Hiatella arctica. 



Tunicates also afford a place of attachment for a variety of animals. 

 The tunic is sufficiently plastic for foraminifers to form depressions 

 to fit their tests. On a specimen of Dendrodoa measuring 35 by 

 16 mm., taken from a depth of 130 feet, the following animals were 

 found : One colony of the bryozoan Eucratea loricata 22 mm. high ; 

 several colonies of the compound tunicate Didemnum albidum, 3 to 

 5 mm. in diameter ; nematodes ; foraminifers on the tunic of Den- 

 drodoa and on the attached Eucratea; two small Dendrodoa; one 

 cirratulid, Chaetoaone setosa; one colony of the bryozoan Tubulipora 

 flabellaris; one hydroid colony ; one sponge spreading over Eucratea; 

 one sponge on the Dendrodoa; one small clam; and several species of 

 encrusting bryozoans. 



Even nonsessile animals often furnish a place of abode for other 

 animals. Snails of the genera Buccinum, Neptunea, Volutopsius, and 

 Boreotrophon seldom are without a colony of hydroids (Hydractinia), 

 bryozoans, or barnacles growing on their shells. 



The legs and carapaces of the crab Hyas coarctatus alutaceus, 

 especially the ovigerous females, furnish places of attachment for 

 many sessile forms, which in turn furnish refuge or places of abode 

 for still other animals. An ovigerous female taken on September 9, 



