//. TYPES IN DETAIL fVITH THEIR SUBORDINATE GROUPS. 15 



Order 2. Gastrotricha A few forms with a ciliated ven- 

 tral surface. These are consid- 

 ered by some as forming an inde- 

 pendent sub-class, closely allied to 

 Rotifera. x Ichthydium. 



Sub-class II. BRTOZOA (POLYZOA) ..Minute forms, usually encased in 



chitinous tubes or " cells." Gen- 

 erally colonial, and then often 

 bearing a superficial resemblance 

 to a hydroid or an alga. Intestine 

 U-shaped ; mouth surrounded by a 

 ridge {lophophore) bearing ciliated 

 tentacles. 



Order i. Phoronidea Worm -like forms, enclosed ir. 



leathery tubes. One genus, Pho^ 

 ronis. 



Order 2. Endoprocta Anus included within the lopho- 

 phore. Tentacles only partially 

 retractile. All marine. 



X Lrnatella, Loxosoma. 



Order 3. Ectoprocta Anus outside the lophophore. 



Tentacles completely retractile. A 

 few fresh-water forms, the rest 

 marine. x Bugula, Plumatella. 



Sub-class II. BRACHIOPODA All marine, depressed in form, 



with dorsal and ventral shells which 

 are symmetrical, but unequal. 

 Mouth situated between two spiral 

 ciliated arms, which lie coiled 

 up in the shell. A large fossil 

 order. Few living. 



Order i . Ecardines Shell without a hinge, x Lingula. 



Order 2. Testicardines Shell with hinge; usually calcare- 

 ous loops to support arms. 



X Terebratulina. 



