KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 63. NIO 2. 47 



Dendrodoa uniplicata var. minuta Bonnevie 1896. 



Syn. Styela uniplicata var. minuta, Bonnevie 1896. 



Distribution: West Spitzbergen, 78° 2' N— 9° 25' E (Bonnevie 1896). — Novaja Zemlja, Murman 

 coast (Redikorzew 1906). 



Remarks. 



The subgroup of Dendrodoa characterized by a branched gonad has, by pre- 

 vious authors, been divided into several species: aggregata, lineata, adolphi, cylindrica, 

 hukenthali, tuberculata, subpedunculata. Of late the validity of the characters distin- 

 guishing them, has been questioned, however, owing to the great variability of the 

 individuals. »The genus Dendrodoa is one of those groups of organisms which the 

 more it is studied . . . the more dubious become the boundary lines of the subgroups 

 into which it may be divided.» (Ritter, 1913, p. 480.) In the present paper only 

 two forms have been considered as distinct species: D. aggregata and D. lineata, the 

 other forms have been treated as varieties of the species aggregata, comparative 

 studies having proved that the characters used in distinguishing the species cannot 

 be regarded as constant. 



The divisions have, in most cases, been based on the number of the ovarian 

 branches, the number of the intermediate longitudinal vessels of the branchial sac 

 and the development of the branchial folds, the number of the tentacles, the condi- 

 tion of the external surface of the stomach, the external aspect of the test. With 

 regard to the number of the ovarian branches it should be noticed that, in well 

 developed specimens of D. aggregata forma typica, the usual number is five (Pl. 3, 

 fig. 43), in young ones it is very often three. But there are also large individuals, 

 typical in other respects, which have three or four ovarian branches and even from 

 seven to nine. 



Ritter has based the formation of the species tuberculata on the characters 

 exhibited by the gonad having more than five branches, the stomach wall having 

 longitudinal folds externally invisible, the surface of the test being regularly tuber- 

 culated and härd. Låter (1913), having examined an extensive material of this form, 

 this author has observed that the variation of the number of the ovarian branches 

 »is so great as to deprive them of much classificatory value» (1. c. p. 483). If we 

 compare the test of the two specimens of D. aggregata forma typica, illustrated by 

 figs. 39 & 40, it will be evident that the test cannot offer any valuable species 

 character, the tuberculation occurring also in the typical form. Though the surface 

 of the test of D. aggregata usually is faintly wrinkled in longitudinal and transversal 

 directions, or sometimes quite smooth, it is very often provided with rather coarse 

 folds or wrinkles and even, as appears from fig. 40, with tubercles. 



Having had occasion of examining specimens of tuberculata and subpedunculata, 

 kindly lent me by Professor Dr. R. Hartmeyer, I can confirm the observation that, 

 as seen from the external side, the longitudinal folds of the stomach-wall are invi- 

 sible, at least in tuberculata. This difference is probably due to some differentiation 



