CHAPTER 4 

 Musculature and Papillae 



Musculature 



The Pogonophora possess a true dermal muscle sac, consisting of smooth 

 muscle fibres. The circular muscle layer lies immediately under the basement 

 membrane of the epidermis and under this again lies the more strongly 

 developed longitudinal layer of the musculature. The dermal muscle sac is 

 most weakly developed in the postannular section of the trunk. 



The circular muscle layer is very thin but it is present in all Pogonophora 

 over the whole of the body. It is most strongly developed over a small region 

 immediately behind the girdles, where its contraction often produces the 

 impression of a waist at this point, especially in preserved animals. The 

 circular muscle fibres seem to be very long thin spindle-shaped cells (Figs. 

 27,29). m nd 



— cut 



Fig. 29. Part of a transverse section of Polybrachia annalata at the level of the bridles. 

 en - ganglionic cell ; cut - cuticle ; ep - epidermis ;/- keel of the bridle ;fn - nerve layer of epidermis ; 

 mb - basement membrane; trie - layer of circular muscle; mdv - dorso-ventral muscle fibres; 

 mf- musculature of the bridle; ml - longitudinal muscle layer; nd - dorsal nerve trunk; per - 

 peritoneum ; ton - groups of epidermal cells especially rich in tonofibrillae ; vd - dorsal blood 

 vessel. (After Ivanov, 1960a.) 



The musculature of the bridle is a specialized part of the circular layer of 

 muscle which forms a thick cushion under the keels (Fig. 29). When this 

 musculature contracts, the pleating of the cuticle which results causes a ridge 

 of epidermis to protrude, on which are situated the cuticular keels. In this 



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