728 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 14 



The zooecia are irregularly hexagonal, but zooecia that are pentagonal, 

 quadrangular and some that are nearly square are not uncommon. This 

 wide variation in shape may account for the differences found in the 

 measurements that have been previously cited in the literature. 



The zooecial walls are usually distinct. The apertural openings in 

 some of the zoaria are found on small raised papillae, distally located on 

 the ventral wall, while in other zoaria there are no papillae, the ventral 

 surface being smooth. In the latter case, the openings are either easily 

 discerned, or are very obscure. One recent author (Silen, 1942:9-11) 

 considers A. polyoum one of the species with a smooth ventral surface. 

 Other authors (Hincks, 1880:501 ; Osburn, 1933:61 ; 1944:16; Marcus, 

 1941:68) have all noted the presence of a raised oral papilla. It is 

 possible that the presence or absence of the oral papillae may be due to 

 the degree of retraction of the tentacle sheath. If so, a given living 

 zoarium could exhibit no oral papillae at one time, and have them at 

 another. 



The tentacle number poses another problem in this species. The vex- 

 ing question is, does this species have a fixed number of tentacles, a 

 variable number of tentacles, or are there two or possibly three species 

 similar in external appearance being lumped together as A. polyoum? 

 The reported tentacle number varies from 12 (Harmer, 1915:38) to 

 20 (Silen, 1942:11). The original description (Hassall, 1841:484, 

 485) reports the tentacle number as 20. If then the number to be con- 

 sidered as correct is 20, what is to be the disposition of those with 16 

 tentacles (Marcus, 1941:68; Rogick, 1949:47), unless A. polyoum is 

 considered as having a wide variation in tentacle number. In order to 

 determine the number of tentacles in the specimens from the eastern 

 Pacific found in the Hancock collection, comprising at this time 9 sta- 

 tions (5 from Alaska, 4 from northern California), a sample of each 

 of the best preserved specimens with the external characteristics of 

 A. polyoum was sectioned. None of the specimens had 20 tentacles. Two 

 Alaskan specimens, one with raised papillae, and one without, had 17 

 tentacles. One Californian specimen with definite oral papillae had 17 

 tentacles. Three others, all from Californian waters, without oral pa- 

 pillae, had 15, rarely 16 tentacles. Until such time as additional material 

 can be obtained of both Pacific and Atlantic origin, the only safe con- 

 clusion is that A. polyoum does have a variable number of tentacles. 



Akyonidium polyoum is widely distributed in the colder waters of 

 both the Atlantic and the Pacific. In the eastern Pacific it has been 



