EHCHINODERMA. 
iON Aa COMMMCHION Ob YOUNG 
HOLOTHURIOIDS. 
By Proressor E. W. MacBripg, D.Sc., LL.D., F.R.S., 
Imperial College of Science. 
(2 Plates.) 
Iv 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-larvai 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 larvee of the Antarctic Expedition we 
described for the first time the occurrence of the free-swimming larve of 
Kehinoidea and Ophiuroidea in Antarctic waters. We can now assert the existence 
of three out of the four types of free-swimming Echinoderm larve 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 larve. 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 
by 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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