XIII] 



SOLENOGASTRES 



309 



l-JL 



shell are very small compared with this secondary shelly tube. This 

 animal is very destructive to submerged wooden structures ; a 

 wooden pile supporting a pier in Vancouver was reduced to a mere 

 sponge work in the space of eighteen 

 months by the ravages of this Mollusc. 

 The burrowing in this case is effected 

 by the rasping action of the anterior 

 margins of the valves of the shell. 



Before we proceed to discuss the 

 highest class of Mollusca which in- 

 cludes the Squids and Cuttlefish, there 

 are two small groups which we must 

 mention, since they cannot be classed 

 either as Gastropoda or as Lamelli- 

 branchiata. These are the Solenogastres 

 and the Scaphopoda. 



Class III. THE SOLENOGASTRES. 



These are small animals confined 

 to the sea and usually found in rather 

 deep water which look at first sight 

 like worms and have nothing in their 

 appearance to suggest that they are 

 allied to Mollusca. When we come to 

 examine their anatomy we find how- 

 ever that they possess an unmistakable 

 radula sac with a radula bearing teeth 

 inside it. Further, many of them possess 

 two comblike gills i.e. ctenidia 

 projecting from the hinder end of the 



body near the anus. They are bilaterally FIG. 141 Solen vagina, the 

 , . , . , i ,i i Eazor-shell, the shell is open- 



symmetrical animals, and they do not 



possess a shell, unless the isolated 

 spiel ues, secreted by the ectoderm cells 



ed and the posterior part of 

 the mantle is torn to admit 

 of this. 



1. Shell. 2. Foot. 3. La- 

 or some species, may be regarded as bial palps. 4. 'Gills. 



5. 

 6. 

 7. 



Bristle in dorsal siphon. 



the forerunner of this. The mantle 



however is represented by a cup-like 



fold surrounding the anus. There is a pericardium, in the roof of 



which the heart appears as a ridge projecting downwards. This 



pericardium is connected with the exterior by two curved tubes 



which serve both as excretory organs and genital ducts, for the 



