14 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 14 



Division II MALACOSTEGA Levinsen, 1909 

 This Division, according to Levinsen, is "characterized by retaining 

 the original frontal membrane in its primitive form and by having the 

 operculum incompletely differentiated from this membrane." Harmer 

 (1926:187) includes the families Scrupariidae, Membraniporidae, Flus- 

 tridae, Onychocellidae, and Lunulariidae. Bassler (1935:22-25) removes 

 the Onychococellidae and Lunulariidae to the Coilostega and separates 

 out from the Membraniporidae the following families : Electrinidae d'Or- 

 bigny, Hincksinidae Canu and Bassler, Alderinidae Canu and Bassler, 

 Hiantoporidae MacGillivray, and Arachnopusiidae Jullien. 



It is quite apparent that much more study will be required before a 

 completely satisfactory classification can be established. The great diffi- 

 culty in arriving at a proper taxonomic arrangement lies in the fact 

 that usually we cannot as yet determine the evolutionary relationships 

 between groups of species, and this difficulty extends throughout the 

 whole phylum. 



In the Malacostega it has generally been assumed that the genus 

 Membranipora is basic because of its simplicity, though recently Harmer 

 (1926:197) and Silen (1942:55) have given the Scrupariidae a more 

 primitive position. It is true that in the genus Membranipora (sens, sir.) 

 there is a vestigial cryptocyst and gymnocyst, no true spines, no avicularia 

 and no ovicells, but at the same time it has as a special character, a 

 twinned ancestrula. In the Scrupariidae the zoarium is erect and the 

 zooecia are tubular, which may be the primitive form of the zooecium 

 and they also lack avicularia and spines. On the other hand Scruparia 

 possesses hyperstomial ovicells which appear to be a specialization. Has 

 Membranipora become secondarily simplified by the loss of structural 

 characters? Has Scruparia developed a hyperstomial ovicell similar to 

 that of other cheilostomes by parallel evolution ? Are the tubular zooecium 

 and erect zoarium primitive as Silen argues; what evidence we have 

 from paleontology appears to be against it. This is a sample of the numer- 

 ous problems involved in bryozoan taxonomy and at present the best we 

 can do is to list the families and genera in what appears to be the order 

 of complexity as a mark of increasing specialization. 



Key TO THE Families of the Division Malacostega 



1. Zoaria erect, uniserial or biserial, no avicularia. . . Scrupariidae 

 Zoaria usually encrusting; if otherwise they are multiserial. . . 2 



2. Ovicells entirely absent 3 



Ovicells present, hyperstomial or endozooecial 4 



3. Gymnocyst wanting or veiy slightly developed. . Membraniporidae 

 Gymnocyst well developed Electrinidae 



