PACIFIC TUNICATA OF U.S. NATIONAL MUSEUM 143 



matter. Mantle yellowish brown to brownish, especially pigmented 

 dark brownish in anterior one-third of body, including both siphons. 

 Eight side of mantle wholly reticulated with fine muscular fibers, the 

 transverse ones remarkably dominant. Anterior margm of mtestinal 

 loop does not reach beyond level of base of atrial siphon. Axis of 

 second intestinal loop passes through the esophageal region. Both 

 hind stomach and middle intestine obscure. Individual 8 mm. long 

 has 21 partly imperfect inner longitudinal vessels on each side; 19 

 dorsal languets counted in this rather imperfectly preserved speci- 

 men. Languets are distal portions of promment ribs supporting low 

 dorsal lamina. About two stigmata in each mesh. Supporting proc- 

 esses of inner longitudinal vessels roundish distally and hold longi- 

 tudinal vessels on their ventral side near distal end; mtermediate 

 papillae absent. Tentacles about 20, larger and smaller ones differen- 

 tiated. Ciliated groove an elongated slit interrupted near middle with 

 two minute openings ; dorsal tubercle apart from dorsal ganglion for 

 length of ganglion, 



67. Ascidia apcrta Sluiter 



FiGTJBE 53 



Ascidia apcrta Sluiter, 1904, p. 38, pi. 2, fig. 4 ; pi. 6, figs. 1-5.— Van Name, 1918, 

 p. 119, fig. 75-76.— Tokioka, 1954a, p. 257, pi. 32, figs. 2-8; pi. 33, figs. 1-A. 



MATERIAL EXAMINED 



Marshall Islands : Rongelap Atoll ; Naen Island, below low tide, in lagoon ; 

 M. W. Johnson, coll., July 12, 1946. Seven specimens ( USNM 11537) . 



Descmptiox. — There are seven specimens from Rongelap Atoll, 23- 

 40 mm. in length and attached to the substratum by the whole left 

 side. 



Branchial aperture terminal and 9-lobed, atrial aperture opens 

 slightly posterior to middle of body and 6-lobed. Both siphons short 

 but stout; lobation of each aperture rather indistinct. Test trans- 

 lucent or transparent, soft, gelatinous, and pale yellowish. Surface 

 nearly smooth, carries no foreign matter. The most striking feature 

 of these specimens is that the mantle is almost completely devoid of 

 body musculature, except for poorly developed siphonal musculatures. 

 Musculature of branchial siphon consists of about 10 fine sphincters 

 confined to distal half of siphon (indicating anterior distal portion in 

 front of peripharyngeal band) ; atrial siphon consists of 2 or 3 

 marginal sphincters and 1 or 2 other fine circular muscles located 

 slightly apart from marginal ones, also 6 groups of fine and short 

 retractors at each interval between lobes. 



Branchial sac of a 25 mm. long individual has 71 transverse vessels 

 and 50 inner longitudinal vessels on each side. Plications absent; 

 4 stigmata in each mesh; intermediate papillae present (fig. 53c). 

 Tentacles about 20, larger and smaller ones differentiated; larger 



