The Ascidian genera Pterygacidia Sluiter, 1904 and Ciallusia van name, 1918

I was strongly impressed by the striking resemblance between the ascidian genera Ciallusia Van Name, 1918 and Pterygascidia Sluiter, 1904 when in 1957 I examined some specimens of Ciallusia longa Van Name, 1918, collected from Philippine waters and deposited at the United States National Museum (Tokioka, 1967: 136). C. longa is closely related with Pterygascidia mirabilis Sluiter, 1904, collected from off Timor by the Siboga Expedition, in general appearance of the pedunculate body, situation of the branchial and atrial apertures, structure of the branchial siphon, arrangement of body muscles divided into parts, and in the essential structure of the branchial sac, alimentary canal and gonads. The former, however, seemed to differ distinctly from the latter in the absence of a pair of remarkable fin-like semicircular extensions of the dorsal lobes of the atrial aperture and in having a series of dorsal languets instead of the dorsal lamina of a narrow, plainly edged membrane. Especially the last difference seemed very significant from a systematic point of view in Ascidiacea, because the plain membranous dorsal lamina is generally considered to be exceptional in the order Phlebobranchia. Recently, I had the opportunity to examine twenty specimens of C. longa collected by the Snellius Expedition on 5 September 1929 at Station 60*, 6°58.0'N 121°52.5'E, in the Basilan Strait between the islands of Basilan and Mindanao, 72-80 m deep. To my surprise, the pair of wing-like elliptical extensions of the dorsal lobes of the atrial aperture which are supposed to be unique to P. mirabilis were found very clearly on 19 of the 20 specimens (fig. 1 A, B). I thought that I found a structure of uncertain meaning on the dorsal side of the body just posterior to the atrial siphon in the specimens of