THE PHYLOGENETIC INTERRELATIONSHIPS OF THE 



RECENT CRINOIDS. 



By Austin II. Clark, 



Assistant Curator, Division of Marine Invertebrates, IT. S. National Museum. 



In the present enlightened epoch of comprehensive zoological 



thought, one is justly considered as antiquated and narrow-minded 

 if, in the study of any group of organisms, careful attention is not 

 given to their fossil representatives. Yet in many cases the com- 

 bination of recent species with their fossil representatives and near 

 relations forms a mass very difficult of mental digestion, and it is 

 found that the best results are attained by studying each component 

 separately and then combining the acquired data. 



The study of the Crinoidea has always been approached from the 

 paleontological standpoint as a natural corollary of the preponder- 

 ance of the fossil over the recent species; but a comparative study 

 restricted to recent forms alone brings out certain points well worthy 

 of consideration, and emphasizes certain facts not so evident if 

 recent and fossil species are studied all together. 



In the present paper all the recent crinoid groups will be taken up 

 and their various interrelationships shown, without reference to any 

 of their fossil relations, as if there were none but recent crinoids, in 

 the hope that this unique and more or less illogical treatment will 

 call attention to certain points hitherto more or less obscured. 



In studying the recent crinoids I have become impressed with the 

 fact that the stems offer the best criteria for tracing out phylogenetic 

 relationships; a critical study of the stems has shown that all the 

 types converge, both phylogenetically and (where observations have 

 been possible) ontogenetically to a common center. -Next in impor- 

 tance to the stems come the basals, and using these two structures 

 alone we can form a very satisfactory phylogenetic tree. 



On the characters offered by the stem and basals, t he recent crinoids 

 fall into three sharply differentiated groups, as follows: 



a 1 . Stem short ami stout, unjointed. /In/opus. 



a 2 . Stem long and slender, with many joints. 



ft 1 . Stein without cirri or nodes; the basals are inclined upward more or less toward 

 a position parallel to the dorso-ventral axis, enclosing a cup-shaped cavity, 

 and form |>art of the lateral body wall. 



Phrynocrinus; Ptilocrinus; Calamocrinus; ITyocrinus; <•• phyrocrinus; 



Bathycrinus; Rhizocrinus- 



b-. Stem with cirri, forming on : more nodes; the basals are horizontal, or have 



become metamorphosed, and d t form part of the lateral body wall. 



< 'omatulida; /'< ntacrinitidse. 



Proceeding- U. S. National Museum, Vol. 38, No. 1732. 



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