Flatworms and Threadworms 311 



(Fig. 199), which practically all live a colonial life. They look something 

 like the hydroid form of Obelia, but their general structure is quite 

 unlike Obelia. Most of them are marine animals, though there are a few 

 types which inhabit fresh water. Polypide is the name given to the 

 soft parts which lie within a coelomic cavity and which is surrounded 

 by the zooecium (body-wall). 



The lophophore ( ) is the crown of ciliated 



tentacles surrounding the mouth. The alimentary tract, retractor mus- 

 cle, and the funiculus (a strand of mesodermal-tissue attached to. the 

 stomach), are shown in Figure 199. There are no circulatory or excre- 

 tory organs. The eggs develop in the ooecium, which is a modified 

 portion of the body-wall. 



Bugula is the usual laboratory example. Certain members of a 

 colony develop jaws for protective purposes. Such jaw-possessing 

 members are called aviculariae. 



Bryozoa are divided into Ectoprocta in which the anus opens out- 

 side the lophophore, and a coelom is present as in Bugula; and Ento- 

 procta, in which the anal opening lies within the lophophore, while the 

 portion which should be a coelom is filled with mesodermal cells. 

 Examples of this type are Pedicellina and Urnatella. 



The Phoronidea, named after an ancient king, Phoronis, consists 

 of the single genus Phoronis. The animals belonging to this group are 

 worm-like and are enclosed in membranous tubes. They live in sand 

 and are supposed to be related to the Ectoprocta. 



The Brachiopoda (Gr. brachion, arm — pous, foot) are shelled marine 

 animals (Fig. 200), but with the shell on the dorsal and ventral portions 

 of the animal, instead of on the sides as with bi-valves. They are usually 

 attached to some object by a peduncle. An excellent example is Lingula, 

 a very old type, which has been found in some of the oldest geological 

 strata, and which differs but little to-day from the oldest fossil-remains. 



The Brachiopoda are not worm-like in any way, but have an 

 uncertain position in classification, and so are included here. 



The Gephyrea (Fig. 201), (Gr. gephyra, mound), often classified 

 under the annelids, are now believed by zoologists to be unrelated to 

 them, but there is even doubt that the various sub-groupings of 

 Gephyrea themselves bear any very close relationship. 



Three groups are usually mentioned : 



(1) The Echiuroidea, in which the adult shows traces of segmenta- 

 tion, a proboscis, and a pair of ventral-hooked-setae and terminal anus. 

 There is a larval trochophore stage. They ordinarily live in crevices 

 of rocks. 



(2) The Sipunculoidea are unsegmented. They possess one pair 

 of nephridia, a large coelom, and an anal opening on the dorsal surface, 

 near the head-end. They usually possess tentacles at the anterior end. 

 They live in sand or bore their way into coral rock. 



(3) The Priapuloidea are also unsegmented, having an anterior- 



