PACIFIC TUNICATA OF U.S. NATIONAL MUSEUM 



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Figure 23. — Didemnum (Didemnum) siphonale, new species: a, central part of colony 

 showing common cloacal aperture; b, finger-shaped prominences on surface of some 

 colonies; c, spicules, X 1800; d, schema showing the section of colony; e, right side of a 

 zooid, X 100. 



abdominal layer; thus abdomens of one to a few zooids are almost 

 entirely surrounded by lacunae, as in species of the genus Le-ptoclmum 

 (fig. 23d^). 



Zooids large; thorax about 450/a in a strongly contracted state, 

 abdomen about 700/a in lengtli. Retractile muscle of moderate length. 

 A small roundish thoracic organ is found near posteroventral corner 

 of tlio widely opened atrial aperture on each side. About 10 (?) 

 longitudinal muscles on each side of thorax. Branchial aperture 

 6-lobed, stigmatal rows 4, about 8 stigmata in each row. Two testicu- 

 lar follicles, proximal portion of vas deferens coils G-7 times. 



Remarks. — The existence of finger-shaped prominences on the sur- 

 face of some colonies, small spicules and large zooids reminds us of 

 Dideinnurrh {Didemnum) apersum Tokioka, 1953, from Sagami Bay. 



