UMBELLULIDAE 273 



Although Pennatularians are rather scarce in oceanic collections, it is questionable whether the 

 picture thus presented of their distribution and numerical occurrence on the sea-bottom is a true one. 

 I have touched on this problem in a recent paper (Broch 1957). It is obvious that the catch depends 

 to a great extent on the gear used, and unfortunately there is at present no gear able to catch more than 

 a small percentage of all the specimens available. Mooring in the mud, flexibility, contractility, and 

 strong holdfasts especially in the larger specimens, all combine to keep the Pennatularians anchored 

 in situ. Some casual catches, nevertheless, show that some species at all events are patchy in occurrence. 

 This is well known of shallow-water species like Pennatula phosphorea, Virgularia and Stylatida 

 among others, and latterly it has been observed in some species of Umbellula; for example, about 

 240 specimens of U. pellucida were taken at St. 194 by the 'John Murray ' Expedition (Hickson 1937), 

 45 U. thomsonii at Discovery Station 342, and 157 specimens at St. 362 by the Swedish Deep-Sea 

 Expedition. 



In this connexion, it should be noted that bottom samplers (grabs) do not catch Pennatularians even 

 at localities where other gear proves them to be comparatively numerous. It is most probable that the 

 larger, slender, very flexible, deeper-living sea-pens cannot be caught by the grabs, which therefore 

 only give a fragmentary picture of the momentary balance in populations of the medium-sized bottom 

 animals. 



In spite of these negative results, however, a review of the many scattered localities (text-fig. 4) 

 gives us a few hints as to the environmental requirements of Umbelhda and the distribution of the 

 species. 



U. durissima has only been captured singly at depths from 1012 to 4474 m. The stem is very flexible, 

 and most specimens evidently escape the usual fishing gear. Curiously enough one of the first 

 specimens was captured in antarctic waters, where the species has never since been observed. All 

 other records are from intermediate depths in the tropical and subtropical regions of the Atlantic, 

 Indian and Pacific Oceans. 



U. thomsonii appears to be plentiful in the deeper waters of the Atlantic and Indian Oceans (from 

 1336 down to 5860 m., mostly below 3000 m.), but from Pacific waters only two young specimens 

 have been recorded from 3750 and 4460 m. The largest catches to date were made by the Swedish 

 Deep-Sea Expedition in the Atlantic Ocean, where at St. 342 (5033 m.) the prawn otter-trawl caught 

 45 specimens, and at St. 363 (5300 m.) 157 specimens. The species appears to avoid territories where 

 arctic or antarctic waters influence the bottom conditions, although low temperatures may not 

 necessarily be the main factor. 



U. huxleyi has been found in a few, very scattered places in the Atlantic, Indian and Pacific 

 Oceans, generally in tropical and subtropical areas at depths between 296 and 1365 m. The widely 

 spread localities and the records only of single specimens were even more conspicuous than in 

 U. durissima, until the remarkable catch made by Dr A. R. Longhurst in 1955 off Bissago I. (Port 

 Guiana), where one haul of the otter-trawl yielded no less than 17 specimens at 600 m. depth. Not 

 only had a ' patch ' been found, but by good fortune the gear also chanced to detach all these specimens 

 from the mud. (Whether this was just a stroke of luck in sampling the elusive benthos is another 

 question.) The catch may indicate that optimum conditions existed here at about 600 m. depth, 

 though on comparison with other records, with one exception situated at greater depths and at lower 

 temperatures, this appears very remarkable. 



Only two very characteristic Umbelhda species have so far been located in the Indian Ocean alone. 

 Several 'species' have been described from the Indo-Malayan region, but most of them must be 

 reduced to synonyms. Hickson (1937) touched on the problem in his own way saying: 'It is verj- 

 improbable that a larger number of specimens belonging to the same genus, and all in approximately 



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