control of coral reefs by boring sponges 29 



Morphology and Physiology of Clionid Sponges 



Sponges of the family Clionidae live in cavities which they exca- 

 vate in a variety of calcareous materials. Living or dead corals (Figs. 

 3 to 5) and mollusks, calcareous worm tubes, calcareous algae, and 

 limestone are inhabited bv the approximately 100 described species 

 of this family. The genus Cliona with about 65 species is the best 

 known of the 13 genera and will serve as the example for the re- 

 mainder of this discussion. 



In their basic structural and functional features sponges of the 

 genus Cliona are essentially similar to other members of the Class 

 Demospongiae, Phylum Porifera. Water currents are propelled 

 through the sponge body in a system of canals by means of the beat- 

 ing of flagella borne individually on collar cells. Each flagellum is 

 surrounded by a collar of cytoplasmic tentacles which help to direct 

 the excurrent flow of water and also assist in the capture of food 

 particles. Water enters the sponge by way of small pores or ostia 

 and leaves by way of larger openings or oscules. The canals are 

 separated into two discrete systems, an incunent system and an 

 excurrent system, and these communicate solely by way of flagel- 

 lated chambers, hemispherical or thimble-shaped (Fig. 8C). Each 

 chamber is composed of numerous collar cells, the flagella of which 

 face the lumen and create a current toward the larger excurrent 

 opening of the chamber. The water which is drawn in through the 

 external pores of the sponge brings oxygen and food particles to 

 the cells. Unicellular algae, bacteria, and possibly detritus make up 

 the food of clionids as well as of most other sponges. The boring 

 sponges, therefore, do not obtain nourishment from the soft parts 

 of the animals whose shells or skeletons they attack. In some species 

 the sponge may overgrow its calcareous substratum or destroy it 

 completely and live subsequently as a non-excavating, free, massive 

 individual ( Fig. 2 ) . 



Fig. 8. Diagrammatic cross sections through boring stage of Cliona celata 

 Grant. A, section through incurrent papilla (X 10). B, section through excur- 

 rent papilla (X 10). C, section through interior of sponge, showing relation- 

 ship of flagellated chambers with incurrent and excurrent channels (X 96). 

 (A, C modified from Vosmaer, 1933-1935.) 



