OF THE KEEOUELEX KEGIOX OF THE tiKEAT tjOlTHEKN OCEAN. 41] 



Holothurioidka' : 



Chirodota contorta,- Ludwicr. 

 '^Cuciimaria kerguelensis, Tlu'-el 



Ivergiifleu specimens as ;i ilitt'erent species [Uummter conhUus], l)r Studek and Mi- Smith eiiuuierate it as a distinct 

 species in their lists of Keiguelen Ecliiiiodernis. . . . From the evidence furnished by the hxrge material collected by 

 the Challenger, there seems but little doubt that species which have thus far been distinguished as ntmuiaUr iiitstmlis, 

 pluUppii, and cavernosus are all different stages of growth of one and the same species, but owing to the great difierence 

 ill structure between the ambulacral petals of the males and females, and the extraordinary changes this species jiasses 

 through from its youngest stage until it has reached its adult sexual form, it was very natural that those several stages 

 of t;rowth should on scanty material have been regtirded as so many distinct species. The coloi-ation of specimens from 

 different localities appears also ijuite distinct, and in some cases the test and spines are of a light brownish-yellow, in 

 striking contrast to the dark coloured specimens found at other localities.- -(Ac assiz, Zool. Chall. E.vp., part 9, pp. 

 lS3-4.)» 



' The examination of the vast harvest brought home by the Challenger Expedition from different regions of the 

 world, from the shore as well as from the abysses of the ocean, slunvs clearly that tliose Holotliurids which live in the 

 deep sea have two different derivations. The great majority are Elasipoda, which cannot be derived from the present 

 shallow-water fauna, but must have originated from a past type that certainly bore another stamp. On the other 

 hand, so far as can be judged from the results of the expeditions hitherto made, the remaining Holotliurids met with in 

 the great depths are comparatively few, both in species and individuals, and unmistakably show the closest relation to 

 the present shallow-water fauna ; so that while the Elasijioda have retired towaixi the abysses an infinitely long time 

 ago, the latter have emigrated only at a comparatively much later period. . . . With regard to the bathymetrica 

 distribution of Apoda and Pedata, our jiresent knowledge does not enable us to speak of any results of very general 

 value. However, the Cliallenger Expedition has been successful even in these respects, several important discoveries 

 having been made, proving that the present shallow-water fauna has lar more outposts in the great depths of the 

 ocean than at first supposed. Before the Challenger Expedition set out, only a very few forms belonging to the Apoda 

 and Pedata were known from depths exceeding 100 fathoms, and scarcely one below 200 fathoms. This list [of the 

 species met with in the deep sea at depths from 500 fathoms and under] induces me to believe tlie following remarks 

 to be true, or, at least, to have some probability : 



1. Descendants of the recent shallow- water Holothurioidea have escaped to the greatest depths at which any 

 living Holothurid lias been obtained, viz., 2900 fathoms, but they are by no means so prevalent as the Elasipoda, nor 

 do they form such a characteristic feature in the abyssjil fauna. 



2. Most of the forms met with in the deep sea below ,")00 fathoms are distinct from the sliallow-water species 

 though they belong to the same genera. 



3. Several sjiecies liave a vast batliy metrical distribution, some individuals of them still living near the shore, others 

 having descended without any obvious change in their organisation into the considerable deptli of 51K» to VOl) fathoms 

 or exceptionally even deeper. 



4. A wider distribution seawards of a sjiecies seems to take place preferably in the northern and southern oceans, 

 where the different belts proceeding from the vicinity of land outwards would seem to have in general a greater 

 uniformity in tempi'rature and other physical conditions than in the tropical and subtropical regions, where it is 

 slated that the belts below 100 or 200 fathoms have lost the influence of tlie climate, etc., and present conditions of life 

 far different from those above them. Such forms are Myrotrochm fiiikii from shore to 500 fathoms ; Eihinocucumis 

 lypim from about 40 to 530 fathoms ; Thyone mphinutf hx>m 20 to 672 fathoms ; Holothuna inkatimilis from 10 to 650 

 fathoms ; Holuthiiria trcmida from 20 to 672 fathoms ; Trocltostoma violncea from 20 to 700 fathoms ; Thyomdinm 

 pdluddum from about 30 to 1081 fathoms, etc. The two deep-sea species of Symtpta are scarcely distinguishable from 

 some of the shallow-water species. 



5. Pah'piitidfg, I'studodichopus, Acanthotroi-luiyi and probably even Aitkyrodtrma are the only true deeji-sea genera 

 of Apoda and Pedata, no representatives of them having hitherto been obtiiined near the shore or, at least, from any trifling 

 depth. Species of these genera very seldom seem to thrive at a less depth than 500 fathonjs. 



6. Among the Ajioda the Synaptidw are, with a very few exceptions, shore forms, living near the surface of the sea, 

 while the Molpadid;e are probably in a state of emigration seawards, a great number of them having already reached 

 the abysses and settled there. 



7. The Dendrochirotie and Aspidochirota; are still true shore or shallow-water forms, though there are even here 

 many exceptions, proving that their representatives are thriving even at great depths.— (Th^el, Zool. Chall. Exp., part 

 3U, pp. 1, 2, 6, 7.) 



- It is remarkable that the forms [of Chirodota purpurea] di-edged at the Falkland Islands are devoid of anv 

 sigmoid deposits, while those found by the Challenger Expedition in the Strait of Magellan and at Kergueleu 



