CHAPTER 9 



Classification 



There are about 6,700 species of Echinoidea (Grasse, 1948, p. 162) of 

 which about 600 species are Hving (H. L. Clark, 1946, p, 277), the rest 

 fossil. In the family Arbaciidae, there are 8 recent and 14 fossil genera 

 (H. L. Clark, 1946, p. 306; Mortensen, 1935, M II, p. 547). In the 

 genus Arbacia there are 6 species, all living. All Echinoderms live in salt 

 water. 



The following classification of the Echinoidea is based on H. L. Clark's 

 Catalogue of the Recent Sea Urchins (1925), together with some later papers 

 and personal communications with Prof. Clark in 1936 and 1947. 

 He differs in certain cases from Th. Mortensen, whose classification is 

 given in the Handbook of the Echinoderms of the British Isles {ig2'j), and 

 in his Monograph (i 928-1 951). For simphfication, only species are here 

 listed which occur in regions most visited by investigators from Woods 

 Hole, or which are referred to in this Monograph. All species of the 

 genus. Arbacia are listed. 



Much of the data has been taken from Mortensen's comprehensive 

 Monograph of 1 928-1 951, referred to in the text as M followed by the 

 appropriate volume and page; these references are given after each 

 species, and the reader may here obtain practically all the available 

 information, and references to all the literature relative to that parti- 

 cular species. Many of the references on egg size are from sources not 

 published but obtained through correspondence or from my own notes. 

 When several authorities agree on the size of egg, only one authority 

 is given. 



CLASS ECHINOIDEA (OUTLINe) 



Order I Cidaroida Other genera (6) not described 



Family i Cidaridae Suborder C Camarodonta 



Order II Centrechinoida (Diadematoida ') Family i Temnopleuridae 



Suborder A Aulodonta Family 2 Echinidae 



Family i Centrechinidae (Diadematidae) Family 3 Strongylocentrotidae 



Suborder B Stirodonta Family 4 Echinometridae 



Family i Arbaciidae Order III Exocycloida 



Genus a Arbacia Suborder A Clypeastrina 



Genus b Tetrapygus Family i Clypeastridae 



' Diadematoida, Diadema, etc. should be used instead of Centrechinoida, etc. See foot- 

 note in chapter 2 d, p. 17. 



