l62 ANIMAL LIFE OF THE DEEP SEA BOTTOM 



Whereas the food requirements of sea-cucumbers are fairly modest, the 

 brittle-stars are rather voracious. They live on other small animals — 

 worms, bivalves, and the like — and from their presence in large num- 

 bers, in many parts of the deep sea, it may be inferred that there is 

 there a rather prolific fauna; for a predator must be much fewer in 

 numbers than its prey. In this trawl there were also 12 starfishes, spread 

 over three different species. These, too, prey on other animals, rather 

 voraciously in fact. The remaining echinoderms found here — - a small, 

 irregular sea-urchin and a sea-lily ■ — ■ feed on small organisms rather like 

 the sea-cucumbers. 



At a couple of other stations in the Indian Ocean we caught some other 

 strange sea-urchins; one of them, Pourtalesia auroroe, from 7,250 metres, 

 was 1,400 metres deeper than any previously caught echinoderm. The 

 two other species, though fished at the more moderate depths of 3,000 

 and 4,000 metres, were in every respect far more interesting. Their shells 

 are without the typical oval shape, the anterior part being drawn out like 

 a head on a neck (Fig. p. 161). Moreover, they are extremely rare. Both 

 species were taken by the Danish Ingolf Expedition in the North Atlantic 

 and one has also been found in the southern South Atlantic. This last 

 was first described by Wyville Thomson, one of the founders of deep- 

 sea research, while the other, which had been caught only by the Ingolf, 

 was described by the Dane Dr. Theodor Mortensen. How we wished that 

 we had him on board when we picked the brittle shells of his species, 

 Echinosigra paradoxa, out of the trawl ! Now our brief report of the catch 

 had to suffice. This was just the sort of result we were wanting: to find 

 out how far the various deep-sea animals are distributed. In this case 

 there was a jump from 1,515 metres off southern Iceland to 3,300 metres 

 in the middle of the Indian Ocean. 



But let us take a close look at the catch, beginning with the most primitive 

 group of animals, polyps and sponges. Here we find forms which are also 

 common over the continental slope. There was a large Umbellula, the 

 beautiful sea-pen with its colony of polyps gathered like a composite flower 

 at the top of a long stalk. Sometimes we would obtain a number of these 

 and have the good luck to see them emit a bluish light before they died, 

 and we would picture to ourselves the fascinating sight of the sea-floor 

 five kilometres down covered with them. There were also a couple of 

 colonies of hydroids and a piece of an isis. And as usual there were some 

 glass-sponges (Hyalonema) (Fig. p. 131), which rather horribly live up 

 to their name, the skeleton of the living body tissue consisting of pure 

 silicon, clear as crystal and just as brittle. We had to be very careful 



