54 DISCOVERY REPORTS 



post-abdominal muscles had not occurred and probably the arrangement of zooids in systems with 

 common cloacal cavities had not yet been acquired. It is possible, however, that common cloacal 

 cavities were originally present and subsequently lost, but this seems unlikely for the possession 

 of these structures must be assumed to be useful as they are a common feature in several unrelated 

 groups of compound ascidians. If these assumptions about the origin of Protopolyclinum are correct, 

 the two main lines of the Polyclininae typified by Polyclinum and Aplidium respectively must have 

 acquired common cloacal cavities independently of each other, an interesting case of convergent 

 evolution. 



The presence of a stalk shows a degree of specialization which finds a parallel not in the Poly- 

 clinidae but in the Polycitoridae, where Sycozoa has a similar form. 



Distribution. North end of North Island, New Zealand. 



Subfamily Euherdmaniinae Seeliger, 1906 

 Genus Ritterella Harant, 1931 

 Harant (1931) created the genus Ritterella for a species described and named by Ritter & Forsyth 

 (1917) as Amaroucium aequali-siphonalis . This genus differs from Aplidium (syn. Amaroucium) only 

 in having the two siphons equal and both opening directly on the surface of the colony. Oka (1933) 

 created the genus Sigillinaria for a species S. clavata, the genus being distinguished from Aplidium 

 by the same single character. Sigillinaria is therefore a synonym of Ritterella. This is not always 

 recognized, and some authors use the name Sigillinaria (van Name, 1945; Brewin, 1950), while 

 others use Ritterella (Huus, 1933, Tokioka, 1953). 



Ritterella vestita sp.n. (Text-fig. 10) 



Diagnosis of species. Zooids completely embedded; oral and atrial siphons each with six 

 shallow pointed lobes and both opening directly on the surface; about twenty-four simple oral 

 tentacles; dorsal tubercle with a simple transverse opening; twenty-seven to thirty-four rows of 

 stigmata; stomach with eight to ten longitudinal folds; testis follicles in a long series in the post- 

 abdomen. 



Occurrence. St. 934: North Island, New Zealand, 98-92 m. 



Colony (Text-fig. 10 A). The single specimen, the holotype, which is probably incomplete, 

 consists of a stalk 2 cm. long and about 0-4 cm. in diameter, from the end of which a triangular, 

 expanded head arises, about 2 cm. long and 2-4 cm. wide at the distal end, where the width is greatest. 

 The whole specimen is rough and mottled grey, its appearance being due to the heavy layer of en- 

 crusting broken shell which completely covers the test. The common test itself is clear and the shell is 

 confined to the surface. 



Zoom (Text-fig. 10B). The zooids are entirely embedded in the common test and show no arrange- 

 ment in systems. When exceptionally well expanded the thorax measures about 8 mm., but in most 

 zooids it is more or less contracted and may then measure less than 4 mm. in length. The abdomen is 

 between 2 and 4 mm. long, and the post-abdomen may exceed 10 mm. In the preserved state the 

 zooids are dull orange in colour. The wide oral siphon (o.s.) is terminal, of moderate length, and has 

 six shallow pointed lobes. The atrial siphon (a.s.) lies a short distance back along the dorsal side of 

 the thorax; it also opens on the surface, is short and wide, and has six pointed lobes. The body wall is 

 rather thick and opaque, with up to twenty-five slender longitudinal muscles and many slender 

 circular muscles. The longitudinal muscles converge in the sides of the abdomen and continue along 

 the whole length of the post-abdomen. 





