NO. 1 OSBURN: eastern pacific BRYOZOA — CHEILOSTOMATA 21 



8. Zoarium encrusting only, a pair of low distal tubercles, opercul- 



um with dark brown border fusca 



Zoarium erect from encrusting base; no tubercles 9 



9. Erect part of zoarium forming complex bilaminate frills, zooeci- 



al walls thin, proximal crj^ptocyst narrow. . . . perfragilis 

 Narrow, ligulate or forked, bilaminate erect branches, or en- 

 crusting; proximal shelf broader, walls heavier. . . . savartt 



Membranipora membranacea (Linnaeus), 1767 

 Plate 1, figs. 8 and 9 



Flustra membranacea Linnaeus, 1767:1301. 

 Membranipora membranacea, Hincks, 1884:11. 

 Membranipora membranacea, Robertson, 1908:267. 

 Membranipora membranacea, O'Donoghue, 1923 :26. 



The zoarium encrusts almost any object that will afford attachment, 

 though the surfaces of the broader algae are the usual habitat and here 

 the colonies may cover several square inches. The zooecia are very simple 

 in structure, especially in younger and rapidly proliferating colonies. 

 Characteristically they are elongate-quadrate and straight, with very thin 

 walls and the opesia occupy the whole frontal surface. The gymnocyst 

 and cryptocyst are wanting (vestigial) and there are no avicularia and 

 no ovicells. At each distal corner there is usually a knob or process which 

 appears to be formed by a fold of the terminal wall as the distal side is 

 membranous in younger stages. Occasionally these knobs may be pro- 

 duced into hollow tubes or pointed short spinous processes. Not infre- 

 quently there appears on the frontal membrane, a tall membranous tube, 

 as much as 0.50 mm high, closed at the end, the "tower cells," or 

 "Thurmzooecien" of Nietsche, What may be the function, if any, of 

 these structures, unique among the Bryozoa, is still a question, though 

 they may be homologous with the large chitinous spines of M. villosa. 

 (PI. 1, fig. 11). 



It has been reported from various regions around the world, though 

 with what certainty it is difficult to determine. Definitely it occurs on 

 the coasts of Europe, along the Atlantic coast of North America south 

 to the Caribbean Sea, and on the Pacific coast. It is fairly common along 

 the shores of southern California. Hincks listed it from the Queen Char- 

 lotte Islands and O'Donoghue from Ucluelet, British Columbia, and 

 Robertson recorded it from Alaska, Puget Sound, and California. 



Hancock Stations: 1370-41 and 1406-41, Catalina Island, California, 

 and 287-34, Cedros Island, Lower California. Abundant on the larger 

 frondose algae along the California coast. 



