262 



CHAETOGNATHA THROUGH LOWER CHORDATA: 



BALANOGLOSSUS 

 NUMEENSIS 

 -pharyngeal pore 



genital wing 



with genital pores. 



:^i 



genital folds 



^ 



hepatic coeca^ 



IHh 



(xv< 



GLANDICEPS 





SACCOGLOSSUS 

 PUSILLUS 



BALANOGLOSSUS 

 CLAVIGERUS 



Figure 15.7 External appearance of several acorn worms. (From 

 Malcolm Jollie, Chorciate Morphology, Reinhold Publishing Corp., New 

 York, 1962. After Dowydoff.) 



some; some reproduce asexually by budding (Figure 

 15.8). 



CLASS PLANCTOSPHAEROIDEA (Planctosphaeroids) 



Diagnosis: represented by a few extremely rare 

 transparent, spherical larvae; larvae of hemichordate 

 type, but unlike those of the other two classes; found 

 among marine plankton. 





V/ 



coenecium 



RHABDOPLEURA 



CEPHALODISCUS 



Figure 15.8 General appearance of two colonial pterobranchs and 

 their secreted, common, external skeleton or coenecium. {From Malcolm 

 Jollie, Chordale Morphology, Reinhold Publishing Corp., New York, 

 1962.) 



POGONOPHORA ( Beard Worms) 



Diagnosis: symmetry bilateral; unsegmented; en- 

 terocoelous; round, worm-like tube dwellers; 4 to 

 14 inches long; three body regions consisting of one 

 to many frilled tentacles on the anterior region, a 

 weakly defined collar, and a trunk; no digestive sys- 

 tem or gill slits; strictly marine, most very deep but 

 some in shallower water (Figure 15.9). 



The beard worms were first collected by the Dutch 

 ship Siboga during its 1899-1900 expedition in the 

 vicinity of Indonesia. For many years these worms 

 were considered to be strange members of various 

 phyla. In 1955, A. V. Ivanov, a Russian, finally es- 

 tablished our present understanding of the phylum. 



These mostly extremely deep-sea forms are be- 

 lieved to capture food with their tentacles and digest 



Figure 15.9 tome///sobe//o, a beord worm. (Redrawn from Ivanov.) 



