1O8 A. S. PEARSE. 



altered at once. These appendages are waved quickly at 

 regular intervals while extended. 



Polyonyx is very cleanly. The last leg is not used for loco- 

 motion, but is peculiarly modified, as in many anomurnas, to 

 form a cleaning organ (Figs. 3, 7). The tip is chelate and is 

 provided with peculiar pectinate and plumose setae. The 

 crustaceans use these appendages with great expertness; they 

 can reach all parts of the body with them, even the interior of the 

 gill chambers, and can frequently be seen industriously currying 

 themselves. As a result, the body is always as smooth and 

 clean as new porcelain. Pinnixa apparently takes little care for 

 its cleanliness. Except for the mouth parts, antennae and eye 

 stalks, the body is usually dirty and over-grown with various 

 organisms. A bryozoan completely covered the exposed parts 

 of several of the individuals captured (Fig. 26), a Vorticella-like 

 protozoan was attached to others, and one crab was observed 

 that carried a small clam, Mytilus edulis (Linnaeus), attached to 

 its last leg by byssal threads. Concerning the bryozoan Osborn 

 ('12) says: "Hippuraria elongata is also a commensal living in the 

 branchial chambers of the blue and spider crabs and on the 

 carapace of Pinnixa living in the tubes of Chatopterus." This 

 species is apparently not found except in association with crabs. 



In most of the particulars described the two crustacean tenants 

 in Chcetopterus tubes showed striking dissimilarity, but their 

 feeding habits were very much alike. Both Polyonyx and 

 Pinnixa obtain their food by "net-fishing" (Caiman, 'n, p. 115) 

 like barnacles. The "nets" in both are formed by the endopods 

 of the third maxilliped which are well supplied with plumose 

 setae. A Polyonyx by spreading his nets (Fig. 4) can strain most 

 -of the water passing through the tube where he lives. They are 

 extended laterally and swept together below the body. Captured 

 food is carried against the ventral side of the body where it is 

 scraped from the setae of the net by the mouth-parts. Pinnixa 

 feeds in a similar manner but the nets are raised above the head 

 and swept forward and downward against the mouth. Various 

 small organisms are captured. Eight fresh Pinnixa stomachs 

 were examined on August 5 and found to contain (in order of 

 -abundance) : pieces of algal filaments, diatoms, a flagellate 



