PACIFIC TUNICATA OF U.S. NATIONAL MUSEUM 43 



11. Aniarouciuni constrictum Sluiter 



Figures 12a,c,(l 



Amarouciuiii constrirtuni Sluiter, 1900, p. 17, pi. 1, fip. 8a. — Yau Name, 1918, 

 p. 107. lis. 114. 



MAl'ERIAL EXAMINED 

 Palau Islands: Iwnyama Bay; GVF sta. 134. One colony 5 mm. in length 

 (USNM 11461). 



Description. — Colony small, encrusted, elongated; 5 mm. in length, 

 very thin, containing only 9 zooids (fig. 12a). Test soft, gelatinous, 

 transparent, impregnated with sand grains. No system is seen in 

 arrangement of zooids. Zooids placed horizontally, pale pinkish. 

 Thorax and abdomen of nearly same length, reaching o mm. when 

 measured together. Branchial aperture 6-lobed; atrial aperture 

 roundish and situated at level of second stigmatal row. Atrial lan- 

 guet clearly defined, with simple tip. About 10 longitudinal muscles 

 on each side of thorax. Stigmatal rows 9; 3 rows present in range 

 between anus and posterior end of branchial sac. About 10 stigmata 

 in each row. Six large tentacles seen clearly, also some smaller ones? 

 Ciliated groove an oval opening. Stomach situated near or slightly 

 anterior to middle of abdomen, with posterior margin exactly at 

 middle. From 7 to 9 longitudinal plications, excluding typlilosole, on 

 surface of stomach. Middle intestine distinct; proximal portion of 

 rectum swollen conspicuously, but no caecum is formed there in the 

 contracted state. Postabdomen seems to be of considerable length. 

 Proximal portion filled with mesenchjmie cells. Vas deferens per- 

 fectly preserved, but neither testicular follicles nor ova were found 

 in any zooids examined. 



Remarks. — This species resembles Amarouclum multiiMcatum, in 

 the number of stigmatal rows, but differs in the number of longitudinal 

 plications on the stomach and in the appearance of the test, test quite 

 free from sand grains in the latter. From Japanese waters A. saga- 

 tnlense is also related closely to the present species, especially in the 

 number of longitudinal plications on the stomach, but it bears fewer 

 (7) stigmatal rows and its test is quite free from sand grains. Most per- 

 plexing is the comparison between the present species and A. gldbrutn 

 from northern cold waters. These species resemble each other so 

 closely that the distinction between the tw^o can be made usually only 

 by the presence {A. consti-icfum) or the absence (A. glahrum) of sand 

 grains in the test; but evidently this feature cannot be of absolute 

 significance. The number of stigmatal rows (9 in the present speci- 

 mens, 8 or 9 in both the Chatham and l'hilipi)ine specimens) and that 

 of longitudiiuil i)lications on the stomach (7-9 in the present speci- 

 mens, 10 in the Chatham specimens and 10 (o VI in the Philippine 

 specimens) are applicable to the zooids of A. glahrum. It seems rather 



206-191—67 i 



