//. TYPES IN DETAIL IVITH THEIR SUBORDINATE GROUPS. 1 1 



Class I. CALCISPONGI^ Skeleton composed of calcareous 



spicules, the typical form of which 

 is a three-pointed star. 



Order i. Asconida Wall of sponge not folded — main 



cavity lined with digestive cells. 



X Ascetta. 



Order 2. Syconida Wall of sponge forming oblong 



chambers opening directly into the 

 main cavity. Digestive cells con- 

 fined to the chambers. 



X Sycandra. 



Order 3. Leuconida Wall of sponge with a very thick 



mesoderm, in which are spherical 

 chambers lined with digestive en- 

 dodermal cells. Chambers con- 

 nected with the exterior and with 

 the main internal cavity by branch- 

 ing canals. x Leucandra. 



Class II. SILICISPONGLffl Skeleton composed of silicious 



spicules, often in the form of simple 

 rods, or in some cases showing de- 

 signs based upon the number 6. 



Order I. Tetractinellid^ .... Skeleton containing four-rayed 



spicules. 



Order 2. HEXAcriNELLiDiE Skeleton containing six-rayed spic- 

 ules. X Eupleciella, Hyalonema.' 

 Class III. KERATOSPOIfGI.ffi; Skeleton of chitinous threads form- 

 ing a network, sometimes rein- 

 forced by silicious spicules. 



X Euspongia. 



TYPE III. VERMES. 



A large and heterogeneous group of low Invertebrates placed 

 for convenience under a single Type. Although many members of 

 the group are cylindrical and worm-like in shape, there are many 

 other forms included. They are all soft-bodied, with a thin ex- 

 ternal cuticle, and with no internal skeleton. None are segmented. 



