ECHINODEEMA. 



III.-ON A COLLECTION OF YOUNG 

 HOLOTHUBIOIDS. 



BY PROFESSOR E. W. MACBRIDE, D.Sc., LL.D., F.R.S., 



Imperial College of Science. 



(2 Plates.) 



IN 1908 Professor Jeffrey Bell asked me to report on a collection of young Echino- 

 derms, which had been collected by the National Antarctic Expedition. When these 

 came to hand, they proved to be the post-larval stages of a Holothurioid. To this 

 collection was added a specimen of the Auricularia larva of some Holothurioid, the 

 first to be reported from Arctic or Antarctic waters. In an earlier report (5) by 

 Mr. Simpson and myself on the Echinoderm larvae of the Antarctic Expedition we 

 described for the first time the occurrence of the free-swimming larvae of 

 Echinoidea and Ophiuroidea in Antarctic waters. We can now assert the existence 

 of three out of the four types of free-swimming Echinoderm larvae in these waters. 

 This is important in view of the opinion which has been expressed that all 

 Echinoderms in Arctic and Antarctic waters had developments of the shortened 

 embryonic type without free larvse. I shall, first of all, consider this interesting 

 specimen, and then detail the results of my work on the post-larval stages which 

 were contained in the collection. 



I. AURICULARIA ANTARCTICA. 

 (Plate I., fig. 1.) 



This unique specimen is distinguished above all by the large number of 

 wheel-shaped calcareous bodies which it contains. These are distributed all over 

 the body, but are perhaps most numerous in the anal " field." Each consists of 

 a concave bowl, the sides of which are composed of 11 to 13 "spokes" connected 

 hy a rim. At the bottom of the bowl is the hub which projects slightly into the 

 concavity (fig. 2). Where a view can be obtained from the convex side the hub 

 is seen to consist of a coarse network of calcareous substance. Similar calcareous 

 bodies, but with a larger number of spokes, are described from the larva of Synapta 

 digitata, but this larva differs from that under consideration in the fact that its 



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