Fig. 14.—Bathyteuthis abyssicola. (After Hoyle.)
It seems to be very probable that some day, when the right place and depth are discovered, Spirula may be discovered in great abundance, but we have at present no means of judging whether this will be in very deep water or not.
Almost precisely similar remarks apply to the distribution of the pearly Nautilus. The shells of this Cephalopod are sometimes found in great number on the shores of some of the islands of the Southern Pacific Ocean and the Malay Archipelago, but the living animal is but rarely captured. It has been asserted by some travellers that the pearly Nautilus floats on the surface of the ocean and possesses the power of suddenly diving to great depths on being disturbed; but it must be remembered that Rumphius originally caught his Amboyna specimens of Nautilus in traps set at a depth of 200 fathoms baited with sea-urchins, and that the ‘Challenger’ captured a single living specimen off Matuku island in 300 fathoms.
The probability, then, is that both Nautilus and Spirula should be included in the deep-sea fauna, but we are still in want of a great deal more information concerning their life and habits before this point can be definitely determined.
CHAPTER VII
THE ARTHROPODA OF THE DEEP SEA
The deep-sea fauna seems to be particularly rich in marine Arthropoda, many curious and interesting forms being brought up with almost every haul of the dredge. The Arthropoda, too, being very highly organised animals, afford interesting and instructive examples of the effect of abysmal life in the modification of the sense organs and the production of varieties specially modified for the conditions of the struggle for existence in their strange habitat.
Concerning the groups of Ostracoda and Copepoda it may be said that the evidence is not yet conclusive that they include any truly deep-sea species. The largest known Ostracod, measuring somewhat more than an inch in length and probably allied to the genus Crossophorus, has quite recently been captured by Professor Agassiz at depths of less than 200 fathoms, but he could obtain no evidence that it descended into much deeper water than this.
Mr. Brady, in writing the report of the ‘Challenger’ Ostracoda, came to the conclusion that they do exist in very limited numbers in the most profound depths of the sea; but it is nevertheless quite possible that all the Ostracods brought on deck by the trawl or dredge were really captured either on the way down or on the way up, and are, strictly speaking, pelagic in habit.
Similar caution must be taken in dealing with the Copepoda, an order of Crustacea that is essentially pelagic in habit. The only species that has been regarded as undoubtedly abysmal is Pontostratiotes abyssicola, a form whose carapace and antennæ are armed with exceedingly long and strongly toothed spines, and was found in the mud brought up by the trawl from a depth of 2,200 fathoms.
Calamus princeps, the largest species of its genus of a deep reddish brown colour, may also belong to the fauna of the deep sea, but we have less evidence concerning the habitat of Hemicalamus aculeatus, Phyllopus bidentatus, and some of the Euchætæ.