lanoglossus but have large, conspicuous gill pores. 

 P. flciva is a denizen of tiie Indian and Pacific oceans, 

 and P. hahamensis of the Bahamas and West Indies. 



In addition to nearly one hundred different kinds 

 of acorn worms, the phylum Hemichordata includes 

 a few diminutive colonial members which bear 

 tentacle-studded arms on the second region of the 

 body but lack gill slits. These animals secrete a cover- 

 ing for themselves and live within deep cupshaped 

 cavities in a manner reminiscent of moss animals 

 (bryozoans). Related to this life in a blind tube, 

 each has the anus far forward, just posterior to the 

 arm-bearing collar region, and hence over the edge 

 of the tube opening while the animal is feeding, its 

 ciliated tentacles exposed, creating a current in the 

 water that brings food particles and oxygen. 



Each individual of Cephalodisciis may be li of an 

 inch long, not counting the slender stalk extending 

 down into the depths of the community shelter, there 

 making contact with other neighboring individuals. 

 From the dorsal surface of the second region of the 

 body, Cephalodisciis has two rows of from five to 

 nine arms each, every arm fringed with from twenty- 

 five to fifty tentacles. 



Individuals of Rhabdopleiira are less than ^i,; of 

 an inch long, not counting the stalk. Each bears two 

 comparatively huge, gracefully curved arms with cil- 

 iated tentacles, again on the middle region of the body. 



Both of these colonial hemichordates reproduce by 

 budding and also sexually. Ordinarily a colony con- 

 sists of the matured buds from a single individual. 

 The buds are formed low on the stalk and begin as 

 an extension of the previous animal. The first body 

 division of the new individual proceeds to secrete a 



new addition to the community shelter, and later 

 matures in it — still with the possibility of producing 

 further buds either in the same line or as branches of 

 the colony. 



Rhabdopleiira normani has been collected from 

 west Greenland to the Azores, usually attached to 

 old dead parts of corals. Cephalodisciis is a larger 

 genus, with representatives from the Arctic to the 

 Antarctic, most of them obtained by dredging. They 

 grow on rocks, clamshells, and other firm surfaces. 

 Often, in turn, they are overgrown by hydroids and 

 moss animals, adding to the complexity encountered 

 among the living things on a shell or a stone. 



The acorn worm Ptijchodcra hahamensis of the Ba- 

 hamas and West Indies uses its acorn-shaped probos- 

 cis as a burrowing organ and makes branching U- or 

 Y-shaped tunnels in bottom sediments. (Bermuda. 

 Ralph Buchsbaum ) 



