ANTARCTIC BRYOZOA — ROGICK 299 



Zoarium: The colony forms a flat, nearly circular crust on rocks 

 land other surfaces. Its color varies from dull tan to rose to pale 

 lavender and occasionally even a dull green. Tlie color may vary 

 even in the same colony. The color is due to the thin film of organic 

 matter that covers the otherwise white calcareous skeleton. The 

 largest colony, from Station 240, measures 12 by 15 mm. and has 

 imore than 600 zoids. The convex frontal of the zoids gives a young 

 colony a gently mammilated surface. The surfaces of older colonies 

 are flattened by secondary calcification that reduces the saliency of 

 the ovicells and zooecial frontals. The surface pattern is relatively 

 ^e and quite regular. Chitinous parts (opercula and mandibles) are 

 present but ovicells are empty and polypides are absent. 



Zooecia: Are 4-, 5-, or 6-sided. Those which begin a new radiating 

 row are wedge shaped or 3-sided. In the very young zooecia the mural 

 rim may be slightly salient in places but it generally sinks down to 

 form a valley between zooecia whose frontals rise convexly. These 

 valleys become shallower as the colony ages and secondary calcification 

 sets in. 



The thick zooecial frontal is a beaded or granular tremocyst. Its 

 pores are medium sized, rounded, numerous, fairly close together, and 

 rather evenly distributed. No conspicuous areolae are present, al- 

 though occasional edge pores are slightly larger than the more central 

 ones, particularly in the vicinity of the ovicell. An umbo or mucro 

 is lacking. The compensation sac occupies most of the inner frontal 

 surface. The peristome and ovicell are the most elevated parts of the 

 frontal surface and are thin in young zoids, thick in old ones. Only 

 rarely are peristomial spines found on any zoids, and then only on a 

 few very young marginal ones. They are delicate, long, hollow, 

 hyaline, and 2-4 in number. 



Avicularia: Small oval avicularia occur within the peristomes of 

 all zooecia and are the only type present. They are lodged within 

 the peristomial notch at approximately a right angle to the longitu- 

 dinal zooecial axis. Their spatulate mandibles are chitinized as shown 

 m plate 29, I-L. 



Orifice: The clithridiate or pear-shaped secondary orifice is nearly 

 terminal and surrounded by a medium high, thick-waUed peristome. 

 The distal peristome wall is formed from the walls of the next distal 

 zooecium. The lateral peristome walls are formed by its own zoid. 

 The peristome is interrupted frontally by a sinus in which nestles the 

 oral avicularium. An anomaly, the presence of two oral avicularia 

 within the peristomie of two nearby zoids, occurred in a colony from 

 Station 240. Because of the convergent nature of the peristome walls, 

 the primary orifice is difficult to see. The wider-than-long primary 

 orifice has a medium-sized, weak, low lyrula and two prominent car- 



