Mr. T. H. Stewart on the young state of Ophiocoma rosula. 387 



XXXII. — On the young state 0/ Ophiocoma rosula, and on the 

 Form and Development of the Spines of this Species, ^y 

 T. H. Stewart. 



[With a Plate.] 



On looking over a maundful of trawl-refuse lately, which was 

 obtained by the fishermen from off the Plymouth coast, and 

 principally from near the Eddystone lighthouse, I found fine 

 specimens of Salicornaria farciminoides, around the lower por- 

 tions of many of which a parasitic sponge* was attached. On 

 tearing apart this sponge to look for the form of the spicula, a 

 number of exceedingly small starfishes were found on it. When 

 I first saw them, I fancied that they were young Ophiocoma 

 rosulcE, and subsequent investigation has proved this to be the 

 case ; although on looking at them afterwards with a low power 

 (100 diam.) under the microscope, I was, from the very peculiar 

 form of the spines, led to think them a new species of Ophiocoma. 



It is an interesting and curious fact, that not only have these 

 young starfishes been found in deep water, as at the Eddystone, 

 which is about 50 fathoms, but also in pools left by the receding 

 tide in limestone rocks under the " Hoe,^^ Plymouth, and in this 

 case also crawling on a soft sponge; and I have not hitherto 

 observed them in contact with any harder material. 



The fact of their having been found in two such different 

 localities proves that this Ophiocoma spawns both in deep and 

 shallow water. It is also remarkable that they should in each 

 case have been found on sponge, and that those from the deep- 

 water locality were never seen to crawl on the Zoophyte, but 

 were found exclusively on the sponge at the base. 



They were not stalked, as the late lamented. Prof. Edward 

 Forbes fancied the young of the Ophiocoma might be (however, 

 they may have passed this period), but could crawl about at 

 pleasure, though they did not seem to be very active, and seldom 

 moved unless intentionally disturbed, and were crowded chiefly 

 in the corners of the sponge. 



None of them, however, when roughly handled, showed any 

 tendency to break off their arms. 



The largest of them did not exceed one-eighth of an inch in 

 diameter, including both the rays and disk. 



Their appearance when alive, under the low power of a micro- 

 scope, was a most interesting sight ; and by employing the 

 polarizing apparatus, the colours that the various parts, more 

 especially the spines, exhibited, made them tenfold more beautiful. 



* On submitting this sponge to Mr. Bowerbank, whose judgement on 

 such subjects is always appreciated, he not only kindly examined it, but 

 also pronounced it to be a new sponge. 



25* 



