35 



originally employed in somewhat different 

 context. 



Pogonophora. This is probably the newest 

 phylum in point of knowledge of the ani- 

 mals themselves, as the first species was 

 described in 1914, and most of the present 

 day knowledge is less than a score of years 

 old. Only one classification has been un- 

 dertaken, by Ivanov (1955), and his divi- 

 sion into two orders is accepted here. 



Inasmuch as the synonym Brachiata is 

 not well known for these animals, it has 

 not been used for the one class. 



Echinodermaia. No single satisfactory clas- 

 sification has been found for this varied 

 phylum. The subphyla here accepted (see 

 footnotes) are those of Shrock & Twen- 

 hofel (1953). The classes in the Pelmato- 

 zoa, Homalozoa, and Haplozoa are those 

 of Shrock & Twenhofel (1953), being ex- 

 tinct except for the Crinoidea; in the 

 Eleutherozoa the scheme of Shrock & 

 Twenhofel is modified according to the 

 views of Hyman (1955) to omit the Stel- 

 leroidea and treat Asteroidea and Ophiu- 

 roidea as classes. This makes it necessary 

 also to treat as classes the extinct groups 

 Auluroidea and Somasteroidea. This ar- 

 rangement is admittedly a compromise 

 with more familiar classifications. 



This phylum contains a large number 

 of extinct subgroups, and it is difficult to 

 give full attention to the extinct sub- 

 groups without confusing the classification 

 of Recent ones. The orders accepted here 

 are as follows: In Pelmatozoa, Homalozoa, 

 and Haplozoa, from Shrock & Twenhofel 

 (1953); in Asteroidea, from Hyman 

 (1955); in Ophiuroidea, from Boettger 



(1952) except for removal of Auluroidea; 

 in Echinoidea, from Shrock & Twenhofel 



(1953) for the Regularia and from Hy- 

 man (1955) for the Irregularia (except for 

 removal of Bothriocidaroida after Moore 



Notes on Suhkingdorns and Phyla 



et al. (1952); and in the Holothurioidea, 

 from Shrock & Twenhofel ( 1 953 ) . 



Pterobrancliia. Many writers agree on di- 

 viding the pterobranchs into two groups. 

 The difficulties of describing Rhabdopleura 

 and Cephalodisciis together leads to skep- 

 ticism that they should be considered or- 

 ders rather than classes. In deference to 

 workers in this field, the usual division is 

 adopted, with some misgivings (as in Hy- 

 man, 1959). 



Enteropneusta. Only one class and one 

 order is known in this group. It is some- 

 times left without a name, but Balanoglos- 

 sida is available. It is here used for the or- 

 der, as the phylum name is also familiar 

 at the class level. 



Planctosphaeroidea. This phylum consists 

 of a single species of what appear to be 

 larvae. 



Tiinicata. There appears to be general 

 agreement on the assignment of the tuni- 

 cates to three major classes. The subclasses 

 and orders accepted here are those of 

 Pearse (1949) and others, with addition 

 to the Ascidiacea of an order Octacnemida 

 after Harant (1948). 



Cephalochordata. This group, which is 

 usually included in the Chordata, has at 

 least four available names. Those adopted 

 are the ones most often used at the respec- 

 tive levels. 



Vertebrata. The restriction of this phy- 

 lum to the craniates is explained in a pre- 

 vious section. The classes of Vertebrata are 

 taken from Romer (1945) and Colbert 

 (1955). The orders of these classes are 

 taken from these same works, except that 

 Romer is generally followed where he 

 treats as orders the groups which Colbert 

 lists as subclasses or superorders. 



