CHAPTER XII 

 BEACHIOPODA 



Classification adopted 

 1. Ecardines. 2. Testicardines. 



THE group of the Brachiopoda is, by some zoologists, regarded as 

 being allied to the Polyzoa Ectoprocta. Like the Ectoprocta, the 

 Brachiopoda are fixed by a peduncle or foot which may be regarded 

 as a ventral protrusion from the body. Like them too they possess 

 a lophophore, i.e. a lip surrounding the mouth from which arises 

 ciliated tentacles. They possess a pair of trumpet-shaped execretory 

 organs which also serve as genital ducts, and are therefore coelomi- 

 ducts, not true nephridia, and the nerve centres remain throughout 

 life in connection with the ectoderm. 



Brachiopoda might be regarded as an offshoot from the Podaxonia, 

 and this view is adopted by Lankester (1890). The study of their 

 development therefore becomes a matter of great interest. 



Of only four forms, all belonging to the division Testicardines, is 

 the complete life-history known ; these are Argiope neapolitana, 

 Cistella neapolitana, Thecidium mediterraneum and Terebratulina 

 septentrionalis. The development of the first two has been worked 

 out by Kowalevsky (1874), but he did not employ modern methods ; 

 his researches were carried out a long time ago. The development 

 of Thecidium mediterraneum was described by Lacaze-Duthiers in 

 1869, and only the external features of the development were noted. 

 The eggs in all these three species pass through the earlier stages of 

 their development in brood pouches, and only escape as larvae at an 

 advanced stage of development. But in the case of Terebratulina 

 septentrionalis they are shed into the sea, they adhere for a little 

 time to the chaetae of the mother, and escape as larvae at an early 

 period in development. Of the development of this species we 

 possess two accounts, one describing the external features of the 

 entire development, by Morse (1873), and the other giving the 

 results of the application of modern methods to the embryonic and 

 free-swimming larval stages, by Conklin (1902). This form, therefore, 

 will be selected for special description. 



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