360 BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



II. Psileschara Busk, 1860; Sparsiporina D'Orbigny, 1851 ; Bulbipora 

 MacGillivray, 1895; Plagiopora MacGillivray, 1895; Caberoides Canu, 

 1910. 



The Reteporidae are great builders for their colonies frequently 

 grow as large as the fist. Their reticulated fronds are twisted and 

 folded in every direction and intermingle to form a meandriform 

 ensemble of the most elegant aspect. Their graceful colonies can not 

 be the work of true artists since no matter how beautiful it appears 

 to the eye, the reteporidan structure is only a regular trap. Here 

 diatoms and radiolaria accumulate and woe to the innocent protozoan 

 involved in this labyrinth for it can not escape. Hundreds of tentacles 

 snap up this easily digested prey. In order to build so large an edifice 

 the quantity of nourishment is considerable and the millions of 

 minute organisms necessary for this purpose is beyond the imagina- 

 tion. 



The organization of the reteporidan zooecium is very complicated 

 but this is only the result of the same necessity — the absorption of a 

 large quantity of food. The number of tentacles (11 to 15) is rather 

 small, compared to that of the giant cheilostomes such as Tubucellaria, 

 (22-27), Petralia (23-28), and Umbonula (20-30), but the very small 

 zooecium not only compensates for this apparent inferiority but also 

 offers a more effective superiority because for the same amount of 

 surface the number of tentacles is much greater. 12 Moreover, the 

 reteporidan zooecium has a complex* system of adventitious organs 

 (avicularia) which it develops in the most propitious places. As its 

 relative position in the colonial ensemble is extremely variable the 

 variability of the avicularium is necessarily correlative and indefinite. 

 Their place, their form, and their size are absolutely dependent on 

 the alimentary necessities or of the immediate biologic needs. But all 

 do not have identical function. The frontal avicularia by their 

 incessant movements, facilitate the circulation of the water and drive 

 the prey towards the tentacles in calm waters; in the deeper or 

 sheltered portions of the colony they are larger and more powerful 

 but they are smaller on the contrary on the better exposed zooecia. 

 The large fenestrular avicularia drive the prey into the thousand and 

 one meshes of the network and distribute the zoarial capture. In the 

 vicinity of the fenestrules where well exposed or conveniently oriented 

 they disappear. The oral avicularia are the guardians of the entrance 

 to the compensatrix; they regulate the introduction of the minute 

 drop of water at the moment of evagination; they repulse also the 

 organisms which are too large, for the obstruction of the hydrostatic 

 sac provokes death by asplvyxiation of the polypide buried in its 



11 A zooecium of Petralia measures frequently 1.0 by 0.5 mm. or 0.5 sq. mm. and has 25 tentacles. In 

 Retcpora these measurements are 0.5 by 0.2 mm. or 0.10 sq. mm. with an average of 12 tentacles. There 

 are therefore 5 zooecia with 60 tentacles in Retepora on the same space as one zooecium of Petralia. 



