NO. 3 CASSIDULOID ECHINOIDS — KIER 5 



Cenomanian species, such as the Neocomian PygorhyncJius obovatus 

 Agassiz (chart 2, fig. I), and Phyllobrissus gresslyi (Agassiz) (text 

 fig. 61), the Albian Ochetes morrisii (Forbes) (chart 2, fig. M) and 

 the Cenomanian C atopy gus carmatus (Goldfuss) (text fig. 55) and 

 Catopygus bargesii (d' Orbigny) (text fig. 59). 



Although this study is concerned primarily with the cassiduloids, 

 it is of interest to note that a very similar reduction in pores occurs 

 in the spatangoids. I have not studied as many species of spatangoids, 

 but most of those examined fall into a consistent pattern very similar 

 to that in the cassiduloids. Over a brief period of time, all the 

 spatangoids of the many diverse families undergo reduction of extra- 

 petaloid pores from two to one. This change differs from the cor- 

 responding change in the cassiduloids by occurring later, at the end 

 of the Cretaceous. Furthermore, no buccal pores are introduced. 



It is surprising that this parallelism in reduction from pore pair 

 to single pore within the cassiduloids and the spatangoids has never 

 been observed before. Mortensen (1948, p. 178) noted that several 

 species had been reported as having single pores in the ambulacral 

 plates but considered this fact of no significance. One reason that this 

 trend was not discovered earlier is that many of the figures showing 

 the phyllodes have been erroneous. Cotteau's artist always showed 

 double pores in the phyllodes whether they were double or single. Of 

 the hundreds of species of irregular echinoids figured in "Paleontol- 

 ogie Francaise, Terrain Tertaire," all are shown as having double 

 pores in the ambulacral plates beyond the petals, although double pores 

 do not occur in any of them. Hawkins (1911) in his study of the 

 phyllodes did not study any post-Cenomanian species, or he certainly 

 would have discovered this trend. 



The reason for this change from two pores to one pore in the 

 cassiduloids and spatangoids seems to be reasonably clear. Most of 

 the Paleozoic and early Mesozoic regular echinoids used their tube- 

 feet for breathing as well as for feeding and locomotion. To fulfill 

 the respiratory function, it was necessary that the tube-feet bifurcate 

 in order to maintain two separate currents of water, one with oxygen 

 and one without. According to MacBride (1906, p. 517), in Echinus 

 "the tube-foot is connected by a double canal with the ampulla, the 

 object of which is to assist in respiration. The cells lining it are cili- 

 ated, and produce a current up one side of the tube-foot and down the 

 other, and the double canal leading to the ampulla separates these two 

 currents and prevents them interfering with one another." Therefore, 

 each tube- foot had a pair of pores linking it to the exterior. There 



