CHAPTER III 



PORIFERA 



PoRiFERA (Lat. porus, a pore; ferre^ to bear) were originally 

 classed as colonial Protozoa. Found attached to rocks and other 

 submerged objects, they resemble sea weed and were at one time 

 considered as plants. With the exception of one family they are 

 found in salt water. 



While sponges may reproduce by eggs and sperm, they com- 

 monly reproduce by budding, colonies sometimes reaching a diam- 

 eter of three feet. It is possible to cultivate them artificially since a 

 complete sponge will develop from a single isolated cell. 



There are three kinds of sponges, the horny sponge used in com- 

 merce, the siliceous sponges and the calcareous sponges, the last 

 named having no commercial value. 



Classification 



Class I. Calcarea (Lat. calcarius, lime) with spicules of carbonate of 



lime. 

 Class II. Hexactinellida (Gr. hex, six; aktiriy a ray) with siliceous 



spicules, in six rays. 

 Class III. Demospongiae (Gr. demos, people; sponges, sponge) 



having spicules of silicon, or spongin. 



Characteristics 



1. Sponges are the simplest Metazoa, with two distinct layers, 



ectoderm and endoderm, and an undifferentiated middle layer, 

 the mesoglea — which is filled with spicules of siliceous, horny 

 or calcareous material. They are a community of cells with 

 relatively little division of labor. 



2, There is no true coelom or body cavity, but the internal gastral 



cavity or cloaca ranges from a single tube to many branched 

 chambers. 



a. Ascon — incurrent apertures pass directly into inner space. 



b. Sycon — cell layers folded — ectoderm and endoderm, central 

 space. 



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