ECTOPROCTA. 79 



Sub-order 2. Stelmatopoda (Gymnolaemata). 



Bryozoa with discoidal lophophore, tentacles in a closed circle; 

 mouth without epistome. 



The Stelmatopoda are, with the exception of the Paludicellidce, 

 all marine forms. They are always without the epiglottis-like 

 epistome, and possess a complete circle of less numerous tentacles, 

 which arise from a round buccal disc (fig. 547). In many forms, 

 as in Alcyonidium gelatinosum, Membranipora pilosa, a flask- shaped 

 ciliated canal in the body cavity has been observed ; it opens to the 

 exterior near the tentacles, and probably corresponds to the nephridia 

 of segmented worms. Statoblasts are only rarely present. The eggs 

 usually give rise to ciliated larvae. The colonies are for the most 

 part polymorphic, being often composed of root- and stem-cells, with 

 vibracula and avicularia. The 

 ectocysts are sometimes horny, 

 sometimes incrusted with cal- 

 careous matter, and present 

 great variety of form. 



Tribe 1. Cyclostomata. The 

 orifices of the cells wide and 

 terminal, without movable ap- 

 pendages. Most of the species 

 are fossil. The living species 

 inhabit the Northern Seas. 



Fam. Crisiadae. Colonies erect 

 and jointed. - ' " FlG " ^- pl -^ella 



Mediterranean and North Sea ; canal 

 C. eburnecu L. 



Fam. Tubuliporidae. The zooecia disposed in continuous rows. Idmonea 

 atlantica Forb., Phalangella palmata Wood, Arctic Ocean. 



Tribe 2. Ctenostomata. Apertures of the cells terminal; when 

 the tentacular sheath is retracted they are closed by a circle of spines 

 as by an operculum. Stem-cells and root-filaments frequently occur. 



Fam. Alcyonidiidae. Zooecia united to form gelatinous stocks of irregular 

 form. Alcyonidium gelatinosum L., Northern Seas. 



Fam. Vesicularldae. The zooecia project as free tubes on the branched, 

 creeping or erect colonies. Vcsicularid uva L., Farella pcdioellata Aid., Nor- 

 way, Serialaria Coutinhii, Fr. Mull. 



Fam. Paludicellidse. Fresh- water forms. Paludicella Ehreribergii, Van Ben. 



Tribe 3. CJiilostomata. The apertures of the horny or calcareous 



