PACIFIC TUNICATA OF U.S. NATIONAL MUSEUM 



81 



Figure 26. — Trididemnum savignii (Herdman): Colony collected off NomasakI, Japan. 



of rays on equatorial plane varies from 6 to 8 in Japanese specimens 

 to 10-15 (about 13 on an average) in the Hawaiian specimen, although 

 generally fluctuating between 8 and 12. Density of spicules differs 

 considerably according to colonies, generally speaking they are not 

 particularly dense in any colonies of the present material. They are 

 evenly distributed throughout the test from the bottom to the surface 

 in most colonies, while in two Japanese specimens they are found more 

 densely around respective branchial apertures so that the apertures are 

 seen as white spots to the naked eye. 



Size of zooid differs according to colonies; zooids rather small in 

 some colonies, larger in others; thoraces may attain 550/a in a con- 

 tracted state, abdomens up to 750/1, in length; thus distance between 

 zooids becomes relatively large. Zooids colorless, yellowish white or 

 pigmented dark greenish along the peripharyngeal band in some 

 colonies. Branchial aperture 6-lobed, tip of atrial siphon also 6-lobed 

 in some zooids. About 8 longitudinal muscles and a roundish thoracic 

 organ containing minute spicules at level of second transverse vessel 

 on each side of the thorax. Stigmata, 8-10 in each of three rows. 

 One testicular follicle, sometimes bulb-shaped ; proximal part of vas 

 deferens usually coils 4 to 6 times or more (8 or 9) in Japanese 

 specimens. 



Remarks. — Two Japanese specimens resemble very closely Didem- 

 num {D?demm/7n) misaJciense (Oka & Willey) in the appearance 

 of the colony and probably in color when they are alive. However, 

 the structure of zooids differs distinctly from that of D. misakiense, 

 and is of the typical Trididemnum, having three rows of stigmata 



