LIFE BY THE SEASHORE. 



ing process, and are tubular or almost campanulate. The 

 stem is much branched, after the fashion called pinnate, 



and the cups are alternate. 



The next family is that of 

 the Sertularians (Sertularidae), 

 which includes a large number 

 of forms, usually easy to 

 recognise, and represented 

 both in the living condition 

 on the rocks, and among the 

 dried wreckage of the shore. 

 The cups are entirely sessile 

 and are sunk in the stem, the 

 result being to give the stem 

 and its branches a character- 

 istically stout appearance as 

 compared with the filmy 

 threads of many of the Cam- 

 panularians. The cups usually 

 occur on both sides of the 

 stem, and the zooids are com- 

 pletely retractile, so that after 

 death they are rarely visible. 



The first genus of this 

 family is Sertularella, which 

 contains one or two not uncommon littoral forms. We 

 shall describe only one species, chosen because it is not only 

 widely distributed round our own coasts, but also occurs in 

 most seas. This is S. polyzonias, a pretty straw-coloured 

 zoophyte, which often reaches a considerable size. Like all 

 the members of its genus, it has its little cups placed al- 

 ternately, and this, together with their shape, gives a 

 peculiar and characteristic appearance to the whole colony. 

 Each cup has a toothed margin, and can be closed by an 

 operculum made of several pieces. The different species of 

 the genus are distinguished especially by the shape of the 

 cups. In S. polyzonias these are urn-shaped, and bulging 

 below with a divergent four-toothed aperture. In fact, they 

 somewhat resemble the calyx of the Figwort. The stems 

 are slender and much, but irregularly, branched. 



From the species of Sertularella it is usually easy to 



FIG. 19. Magnified fragment of a 

 branch of Halecium, showing the 

 peculiar tubular cups ami the ex- 

 panded zooids. After Hincks. 



