31 



Cyathospongia. The status and subdivi- 

 sions of this extinct phylum are taken 

 from Okulitch in the Treatise (E, 1955). 

 The oldest of the three names for the phy- 

 lum is accepted here. (Archaeocyatha 

 remains as a class). 



Mesozoa. In adopting this phylum most of 

 the views of Hyman (1940) are accepted, 

 except that the two orders are deemed to 

 be amply distinct in basic development and 

 histology to be treated as classes. This is 

 the arrangement of Lankester (1901). It is 

 also believed that Lankester was justified 

 in separating the Heterocyemida from the 

 other Dicyemida, and they are accordingly 

 given ordinal rank; for this class the name 

 Rhombozoa is available. 



Monoblastozoa. (See remarks under 

 Phyla, above.) 



Graptozoa. The orders are taken from the 

 Treatise (V, 1955). 



Conularida. This arrangement is taken 

 from the Treatise (F, 1956), but the treat- 

 ment as a phylum is new here (see remarks 

 under Phyla, above). 



Coelenterata. The classification of the 

 classes of this phylum adopted here is the 

 usual one except for two features: 1] two 

 extinct classes are added, and 2] one 

 group often listed as an order or subclass 

 is given class rank. The first two classes 

 are dealt with as in the Treatise (F). The 

 third one requires discussion here. 



Stromatoporoidea. This group has re- 

 cently been included in the Hydrozoa. The 

 principal arguments in favor of this seem 

 to be that there are other Hydrozoa show- 

 ing some of the same peculiar colonial fea- 

 tures. It appears that this is an argument 

 for re-examining these other groups (such 

 as Spongiomorphida), because their pre- 

 served hard-parts show few features of 

 Recent Hydrozoa. It seems best to empha- 

 size the considerable structural differences 

 between stromatoporoids and typical hy- 

 drozoans by not merging them in one class. 



The only reasons that can be given 

 for retaining the stromatoporoids in the 

 Coelenterata while removing the grapto- 

 lites from that phylum are that the grap- 

 tolites form a somewhat more distinct 

 group and that the recent extreme diver- 

 gence in views on their position in the Ani- 

 mal Kingdom lend credence to their more 

 isolated position. Retention of the stroma- 

 toporoids does not at present alter the defi- 

 nition of the Hydrozoa. 



Notes on Subkingdoms and Phyla 



The orders of Stromatoporoidea are 

 accepted from Shrock & Twenhofel (1953) 

 after Kuhn (1939). Other recent works di- 

 vide the group into families, using no or- 

 ders. The orders of Hydrozoa are those of 

 Hyman (1940) plus the extinct Spongio- 

 morphida. The orders of Scyphozoa are 

 those of Hyman (1940) plus the extinct 

 Lithorhizostomeae, being thus those listed 

 in the Treatise (F) after the removal of the 

 Conularida. The orders of Anthozoa are 

 those of the Treatise, and they are those of 

 Hyman (1940) except for the Cerianti- 

 patharia and the extinct orders. 



Ctenophora. The classification of Hyman 

 (1940) is accepted both as to classes and 

 orders. Nearly all recent works agree on 

 this arrangement. 



Platyhelminthes. Three classes are gener- 

 ally recognized here, but the most recent 

 monographic work on the tapeworms 

 (Wardle & McLeod, 1952) seems to justify 

 the recognition of the Cestodaria as a class 

 distinct from the Cestoda. Hyman (1951) 

 included these in the Cestoda as a subclass, 

 but she found them sufficiently distinct to 

 require separate treatment in all respects 

 from the rest of the tapeworms (Euces- 

 toda). 



At one time the Temnocephaloidea 

 were treated as a class intermediate between 

 Turbellaria and Trematoda. Although it 

 has been claimed that this arrangement is 

 now abandoned by all workers, it does re- 

 appear in Dawes' (1946) monographic 

 study of the Trematoda. In deference to 

 Hyman's studies on the Turbellaria, the 

 group is herein placed in the Turbellaria 

 as a suborder of Rhabdocoela. 



The orders of Trematoda are taken 

 from Dawes (1946), of Cestoda and Ces- 

 todaria from Wardle & McLeod (1952), 

 and of Turbellaria from Hyman (1951). 



Rhynchocoela. Many recent works have 

 divided this phylum into two classes, the 

 Enopla and the Anopla. While accepting 

 this subdivision, Hyman (1951) considers 

 "the great similarity of structure through- 

 out the phylum" as reason for not making 

 these two groups classes. She therefore lists 

 them as subclasses, there being no class 

 mentioned. There is no rule preventing the 

 subdivision of a phylum directly into sub- 

 classes, but it is unfamiliar and disconcert- 

 ing. 



The features cited by Hyman as dis- 

 tinguishing the two subclasses seem to be 

 no more fundamental than those used for 



