3. THE INTEGUMENT AND ASSOCIATED STRUCTURES 



35 



Fig. 23. Epithelium of the dorsal ciliated band of Lamellisabella zachsi. 



cc - ciliated cell ; cil - cilia ; en - ganglionic cell ; cut - cuticle ; mb - basement membrane ; mc - layer 



of circular muscle; ml- layer of longitudinal muscle; pn - nerve fibres. (After Ivanov, 1958b.) 



varies considerably from one part of the body to another; as a rule it is more 

 strongly developed at the front end of the body and on the ventral side. In 

 the larger species {Spirobrachia grandis and Lamellisabella) it reaches its 

 greatest development in the zone of attachment of the tentacles and on the 

 tentacles themselves, joining them together rather firmly. But without doubt 

 the cuticle possesses great elasticity and extensibility, as testified by the 

 powerful subcutaneous musculature and by the longitudinal muscle fibres of 

 the tentacle. The substance of the cuticle gives a positive periodic-Schiff 

 reaction, i.e. it contains polysaccharide (Figs. 21, 28). 



Amongst the undoubted derivatives of the cuticle we may enumerate the 

 keels of the bridle and the plaques of the adhesive papillae. 



The keels of the bridle 

 The keels of the bridle (cf. p. 13) appear as simple thickenings of the 

 cuticle projecting more or less above the surface of the body and possessing 

 their own yellowish, brown or black pigmentation (Fig. 29). In a few larger 

 species they are considerably thickened: in Lamellisabella johanssoni the 

 height of the keels reaches 140>. In such a species the keels possess a more or 

 less lamellar structure with parallel layers of cuticular substance arranged 

 along the keel perpendicular to the body 

 surface. In the tiny Siboglinwn minutum the 

 keels are very delicate, each seeming no 

 more than a thin cuticular thread broken up 

 into small rodlets (Fig. 24). In Diplobrachia 

 irregular cuticular corpuscles are attached 



| 0.03mm 



Fig. 24. Keel of the bridle of 

 Siboglinum minutum, greatly 

 enlarged. (After Ivanov, 1957a.) 



