PRIAPULOIDEA HABITS 



433 



It will be noticed that with the exception of P. tuberculato- 

 spinosus, described by Baird from a single specimen, the whole 

 family is confined to northern seas. 



Habits. The newly-captured specimens of both P. caudatus 

 and H. spinulosus are of a flesh colour, with a somewhat metallic 

 sheen. According to Apel, the latter lived 

 in an aquarium for more than five months, 

 whilst the former died during the first 

 month. When first introduced into the 

 aquarium they immediately began to busy 

 themselves in the mud or sand at its 

 bottom, and very seldom showed themselves 

 above it. They forced their way into the 

 sand by alternately contracting and extend- 

 ing their introvert, and the Priapulus 

 arranged itself so that a portion, often a 

 very small one, of its caudal appendage was 

 exposed to the water ; this fact supports the 

 view that the appendage is respiratory in 

 function. When the animal buries itself 

 deeply, the appendage does not relinquish its 

 position at the surface of the sand, but 

 stretches itself until it in some cases sur- 

 passes the length of the body. On the other 

 hand, Halicryptus (Fig. 219), according to 

 the same observer, lies with the anterior 

 end, the mouth, projecting from the surface 

 of the sand, or else it curves itself, so that 

 both ends project into the water. 



Leckenby, who described specimens of P. caudatus which 

 were found by fishermen searching for worms for bait in the 

 outer harbour at Scarborough at half tide, states that they live 

 in sandy clay in U-shaped tubes, at a depth of about 9 inches, 

 the tubes opening at each end on to the surface of the sand. The 

 fishermen of this district call them " sea mushrooms." 



Halicryptus casts its cuticle in May and September; it 

 becomes loose first at the hinder end, and the split between it 

 and the skin grows forward until the animal lies free in a 

 cuticular mantle. After some days this is split, and the animal 

 frees itself from it ; the cast-off cuticle includes for a short dis- 



VOL. n 2 F 



spinulosus v. Sieb. x 6. 

 , Dark line indicating 

 the position of the 

 ventral nerve-cord ; d, 

 mouth surrounded by 

 spines. 



