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



Ord. Ptychobranchia. 



Fam. Styelidae. 



Branchial sac with from 1 to 4 folds on each side, or without folds, (a rudi- 

 mentary fifth fold in one species onlj 7 ). Stigmata usually straight, longitudinal. 

 Internal longitudinal vessels numerous. Tentacles simple. Alimentary canal on 

 the left side of the branchial sac, in one genus posterior to the branchial sac. Stomach 

 distinctly marked off from the intestine, with longitudinal folds, no »liver». A small 

 pyloric coecum present in many species. Reproduction by generative organs only, 

 not by budding. Reproductive organs short polycarps or elongated gonads, un- 

 divided or divided into branches, placed on one or on both sides, within the body. 

 No genital pouch and no brood-pouch are developed. Apertures four-lobed. Test 

 leathery. Body usually attached, of various form. Individ u als solitary or aggre- 

 gated into groups, not forming colonies. 



»Synopsis of genera and species. 



I. Reproductive organs on both sides of the body. Vasa efferentia join to 

 form a vas deferens, running on the inner free surface of the ovary. 1 

 A. Testis separated from the ovary and situated at the side of it. 



1. Branchial sac with four well developed folds. Gonads one or two 

 on each side of the body. Alimentary canal on the left side of 

 the branchial sac. Styela Fleming 1822. 



2. Branchial sac without folds. One gonad on each side, consisting 

 of an elongated U-shaped ovary bordered on either side by male 

 glands. 2 The greater part of the alimentary canal posterior to the 

 branchial sac. Pelonaia Goodsir a. Forbes 1841. 



1 In the descriptions of Styela yelatinosa Traustedt, Styela doliolum Bjerkan, Styela bathybia Bon- 

 nevie, nötning is mentioned as to the structure of the vas deferens. There is, however, reason for supposing 

 that these species agree with other Styelae in this respect. 



- van Name, W. G., 1912, p. 546, text-fig. 29, has figured the gonads of P. corrugata as elongated, 

 straight structures what probably may be a mistake. As far as I can see, no other author has observed this 

 form of the gonad in that species. 



