CLASSIFICATION OF THE ANIMAL KINGDOM 



32 



distinguishing the orders. It is therefore 

 here considered preferable to consider the 

 nemertines as consisting of a single class 

 of four orders. (The orders are those cited 

 byHyman, 1951.) 



Inasmuch as there are two well-known 

 names available for this one-class phylum, 

 it seems reasonable to retain one for the 

 phylum and the other for the class. There 

 is little reason to choose either way, but 

 Hyman's argument that Schultze (1850- 

 51) was the "zoologist who first clearly 

 understood the group" may be used as 

 justification for adopting Schultze's name, 

 Rhynchocoela, for the phylum. 



Acanthocephala. This is another one- 

 class phylum, for which no class names are 

 available. The orders are listed as in Hy- 

 man (1951). 



Rotifera. The decision made above, not 

 to employ the Aschelminthes for six groups 

 of pseudocoelomate animals, results in 

 elevation of these six groups to phyla. This 

 raises the question of whether the orders of 

 the former class Rotifera should be raised 

 to classes. This has been done by some 

 classifiers, but there is considerable hesi- 

 tation to doing so here. The Seisonidea 

 appear from Hyman's remarks to be suffi- 

 ciently distinct to be considered a separate 

 class, but it is not so clear that Bdel- 

 loidea and Monogononta can be distin- 

 guished by equally fundamental characters. 

 In this dilemma, the three groups are ten- 

 tatively treated as classes, with the three 

 groups within the Monogononta treated as 

 orders. 



Gastrotricha. The differences between the 

 two groups of gastrotrichs, as described by 

 Hyman, including the protonephridia, 

 pharyngeal pores, and the body cavity sub- 

 division, appear to justify the elevation of 

 the two groups to the level of classes. Each 

 then consists of a single order. 



Kinorhyncha. Although this group is here 

 considered to be a distinct phylum rather 

 than a class of Aschelminthes, there seems 

 to be no reason for not following Hyman 

 (1951) in considering its subdivisions as 

 of less than ordinal rank. The characters 

 distinguishing the three subdivisions are 

 principally matters of degree, including 

 no fundamental clear-cut distinctions. 



As the phylum must contain at least 

 one class, there seems to be no reason for 

 not using the name Echinodera at this 

 level. It remains effectively a synonym of 

 Kinorhyncha. 



Priapidoidea. The three known species be- 

 long to two genera. There appears to be 

 no basis for separating these at the ordi- 

 nal level (Hyman, 1951), and therefore 

 there is a single class with one order. 



Nematoda. Although the treatment of 

 this group as a phylum differs from Hy- 

 man's (1951) treatment of it as a class of 

 Aschelminthes, her view is accepted that 

 there are no subdivisions worthy of rank 

 above the ordinal level. The single class 

 can be distinguished from the phylum by 

 the older but less familiar spelling Nema- 

 toidea. 



Gordiacea. There appears to be little of 

 basic nature in the differences between the 

 Gordioidea and the Nectonematoidea. Hy- 

 man (1951) is therefore followed in plac- 

 ing these as orders, although in the status 

 of the group as a whole a different view is 

 adopted (see Aschelminthes, above). 



Calyssozoa / Endoprocta. A single class 

 and order make up this phylum, and the 

 only questions which arise are about the 

 names to be used. The order has been 

 called Pedicellinida by Boettger (1952), 

 the name Entoprocta or Endoprocta has 

 generally been used for the class, and the 

 first name proposed for the phylum is 

 Calyssozoa of Clark (1921). It seems least 

 confusing to accept these rather than dup- 

 licate one name at several levels. (The 

 spelling Endoprocta is here preferred over 

 Entoprocta because of its greater difference 

 from Ectoprocta. 



Bryozoa. Hyman's (1959) division of this 

 phylum into two classes with six orders, 

 following many earlier workers, is ac- 

 cepted here, as in most current paleonto- 

 logical works. 



The single order of the Phylactolae- 

 mata seems to be without a name. The 

 name first used for the group was Lopho- 

 poda, abandoned by later workers in favor 

 of Phylactolaemata. It is here revived for 

 the ordinal level. 



The argument for replacing Bryozoa 

 with Ectoprocta because of removal of the 

 Endoprocta has been answered above un- 

 der Coelenterata. Removal of one group is 

 not considered justification for changing 

 the name of a phylum (or other taxon) . 



Phoronida. The two genera seem to be- 

 long to a single order, for which there is 

 no special name (Hyman, 1959). 



Brachiopoda. There appears to be univer- 

 sal agreement as to the division of this 



