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53
Basaldel er ganske smal og Endedelen sammensat af 12
med lange Svømmebørster forsynede Led.
Bagkropslemmerne er af den for Hunnerne af denne
Familie sædvanlige rudimentære Beskaffenhed, kun dannende
lancetformige, med tint cilierede Børster besatte
ubevægelige Plader.
Det midterste Halevedhæng (PI. Y, Fig. 20) er af
et meget eiendommeligt Udseende og uligt samme hos de
ovrige bekjendte Mysider. Det er ganske kort, pladeformigt
og næsten qvadratiskt, kun ubetydeligt afsmalnende mod
Enden, der i Midten er dybt indskaaret. Indsnittet, der
omtrent indtager l/3 af Vedhængets Længde, er vinkelformigt,
med Kanterne næsten lige, stærkt divergerende og i hele
sin Længde fint saugtakkede. Paa Spidsen af enhver af de
triangulære Endefliger staar en enkelt Torn og foran denne
er til Sidekanterne fæstet en Rad af 8—12 meget smaa
Torner. der dog kun naar omtrent til Midten af Vedhængets
Længde.
De ydre Halevedhæng (Fig. 21) har Endepladerne
temmelig store, af lancetdannet Fonn og rundt om besatte
med de sædvanlige Randbørster. Den indre Plade er noget
kortere og smalere end den ydre og viser ved Basis kun
en yderlig svag Antydning til det sædvanligt her
forekommende Høreapparat. Dens indre Kant er under
Rand-borsterne næsten i sin hele Længde forsynet med en Rad
af korte Torner.
Paa det under vor Expedition erholdte Individ var
hele Legemet gjennemsigtigt, af hvidagtig Farve og uden
det mindste Spor af nogen Pigmentering.
Længden af det største af de to foreliggende
Exemplarer synes at have været omkring 35"""; men det var
endnu ikke forsynet med tydeligt udviklede Æggeplader og
kan derfor heller ikke antages at have naaet sin fulde
Størrelse.
Forekomst og Udbredning. Af denne mærkelige
Myside blev et enkelt Exemplar under Expeditionens sidste
Togt optaget ved Hjælp af Trawlnettet fra det enorme Dyb
af 1110 Favne i Havet NV af Finmarken (Ståt. 295). Det
andet mindre Exemplar blev, som ovenfor anført, fundet af
R. Collett i Ventrikelen af Rhodichthys regina, der
optoges paa den længere vestlig beliggende Ståt. 297 fra et
endnu større Dyb, nendig 1280 Favne. Ogsaa dette
Exemplar var selvfølgeligt incomplet, men viste dog de
forskjellige Kropsvedhæng bedre vedligeholdte end hos det andet.
At denne Myside er en i ganske særlig Grad udpræget
Dybvandsform, fremgaar ikke blot af Findestederne, men
ogsaa af flere Punkter i dens Organisation, navnlig de
fuldkommen rudimentære Øine, de tynde Integumenter og Mangelen
af Pigmentering. Da begge Stationer tilhorer den kolde Area,
maa den desuden antages for at være en ægte arktisk Form,
der rimeligvis er udbredt over hele det dybe Havbasin i
Nordhavet.
elongated, being considerably longer than even the stem of
the leg itself. Its basal part is rather slender, the terminal
portion consisting of 12 articulations, furnished with long
natatory bristles.
The abdominal limbs exhibit the usual rudimentary
character observed in the females of this family, forming
merely small, lanceolate, immobile plates, beset with delicately
ciliated bristles.
The telson (PI. V, fig. 20) presents a very peculiar
appearance, unlike that exhibited in any other known
Mysidian. It is exceedingly short, lamelliform, and almost
quadrate, tapering but slightly toward the extremity, which, in
the middle, appears deeply incised. The incision, which ocupies
about one-third of the length of the appendage, is angular
in form, with the margins almost straight, very considerably
diverging, and, throughout their entire length, finely serrate.
From the point of each of the triangular terminal lobes,
springs a single spine, anterior to which are attached along
the lateral margins a row of 8—12 very small denticles,
reaching only however to about the middle of the appendage.
The outer caudal appendages (fig. 21) have the terminal
plates rather large, lanceolate in form, and beset round the
edges with the usual marginal bristles. The inner plate is
somewhat shorter and narrower than the outer, exhibiting
at the base but an exceedingly faint indication of the
auditory apparatus that usually occurs here. The inner border
is provided beneath the marginal bristles, throughout its
entire length almost, with a row of short spines.
In the specimen obtained on the Expedition, the whole
body was translucent, whitish, and without the slightest
trace of pigment.
The length of the largest of the two specimens
examined, would appear to have reached about 35"""; but as
yet the animal was not furnished with distinctly developed
incubatory plates, and can hardly therefore have attained
its full size.
Occurrence and Distribution. — Of this remarkable
Mysidian, a single specimen was taken, in the trawl, on
the last cruise of the Expedition, at the enormous depth
of 1110 fathoms, in the open sea, north-west of Finmark
(Ståt. 295). The other and smaller example was. as
previously stated, found by Mr. R. Collett, in the ventricle of
Rhodichthys regina, brought up at Ståt. 297, lying farther
west, from a still greater depth — viz. 1280 fathoms. This
specimen, too, was of course defective, but had the various
appendages to the body in a better state than the other.
That the Mysidian treated of here can in a special
degree lay claim to the character of a true deep-sea form,
appears not only from the localities where it. was met with,
but also from divers characteristics in its organization, viz.
the wholly rudimentary eyes, the very thin integuments, and"
the absence of pigment. Both Stations being in the cold area,
it must, moreover, be regarded as a true Arctic form,
distributed in all probability throughout the whole of the
deep basin of the Northern Ocean.
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