HOLOTHURIOIDEA 355 



Auricular ia (Fig. 3, 1). It has no skeleton, only scattered cal- 

 careous spicules, usually elegantly shaped wheels. From the 

 Asteroid larvae, which likewise lack a skeleton, the Auricularia 

 is distinguished by the preoral part of the ciliated band (the 

 frontal area) not being separated off from the ciliated band of 

 the dorsal side, but being in direct continuation therewith at 

 the anterior end of the larva. No Dendrochirote is known to 

 have an Auricularia larva ; the species of this group appear all 

 to have direct development, with a simple, barrel-shaped (mostly 

 red) larva, provided with ciliated rings. On metamorphosis the 

 Auricularia undergoes a remarkable change ; the ciHated band 

 partly dissolves and the remaining parts arrange themselves so 

 as to form rings round the body, which now becomes fusiform ; 

 this stage is designated the pupa stage. Some Auricularias 

 reach a fairly large size ; Auricularia nudihranchiata Chun 

 reaches a length of 6 mm., and a related Japanese species even 

 15 mm. Another fairly large form is the Auricularia antarctica 

 MacBride, w^hich is up to 4 mm. long. 



The only Auricularia recorded from the British seas is that 

 of Lahidoplax digitata, which has been observed by Chadwick at 

 Port Erin in the month of July. There can, however, be no 

 question but that at least one more kind of these larv^ must 

 occur there, namely, that of Holothuria Forskali. Possibly also 

 Auricularia nudihranchiata may occur there ; this larva, which 

 was originally found at the Canaries, has been found at the 

 Azores, and even as far north as 45° 32' JST., 25° 50' W. It 

 would therefore not seem unreasonable to expect it to occur 

 also near the Irish west coast. It is not known to which 

 Holothurian this larva belongs ; probably it belongs to some 

 deep-sea Holothurian. 



Key to the Auricularias known from or likely to occur 

 in British seas. 



1. No wheels present, only a star-shaped spicule in the posterior 



end ; the body very simple, H-shaped, the vibratile band 

 running nearly straight forwards and backwards 



Holothuria Forskali 



Wheels present, no star-shaped spicules ; vibratile band forms? 



a number of simple or folded lobes .... 2 



2. Lobes of ciliated band simple (Fig. 3, 1) ; wheels present only in 



postero-lateral lobes .... Lahidoplax digitata 



Lobes of ciUated band very strongly folded ; wheels scattered 



irregularly all over the body . . Auricularia nudihrarichiata 



The Holothurians are very sluggish animals, which Live buried 



