Nema Todes Parasitic on Sea Weeds of the Genera Ascophyllum and Fucus

In 1892 Barton described galls found on the sea weed Ascophyllum nodosum from the Isle of Cumbrae, west coast of Scotland, and from Stonehaven, east coast of Scotland. The affected areas on the thallus of the plant appeared as swellings covered with small rounded nodules, and were almost invariably confined to the parts of the thallus just above or below the air vesicles. A transverse section through the swellings showed each nodule as a more or less hollow space containing numerous nematodes, specimens of which were sent to J. G. de Man, who (1892) described the worm as a new species, Tylenchus Jucieola, the first-known marine tylenchid. On the basis of de Man's description Cobb (N. A. Cobb in M. V. Cobb, 1933) erected the genus Halenchus for this species. Since then, other species of Halenchus have been described, but only as free-living forms. From time to time galls on other sea weeds have been reported, but attributed to other animal agents, bacteria and fungi. During visits by the author to the Laboratory of the Marine Biological Association at various times during 1955-57 galls were found very commonly on Aseophyllum nodosum in the Plymouth area (Wembury Bay). They agree well with Barton's description and contain numerous specimens of a nematode, which appears to be identical with de Man's form. Similar galls were also found at Croyde Bay on the north Devon coast in August 1955 (Fig. I A). Galls were also found on the sea weed Fueus vesieulosus (Fig. I B) from Wembury Bay, Devon, and at Hannafore, Looe, Cornwall. They were found only on the older growths of the plant and occurred mainly on the stipes, and less frequently on the base of the fronds. The galls are quite noticeable and are usually a little lighter in colour than the rest of the stipes, but are not so large as some of those seen on Aseophyllum. The surface of the swellings is rugose and not so papillate as the galls on the other plant. When the galls were opened nematodes were found, but there were only a few in each in contrast with the galls on Aseophyllum which contain large numbers. At first the worms were thought to be identical with Halenchus Jucieola, except that the anterior end appeared rather larger. On closer examination, however,