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102
finde vi, omend ikke i den Størrelse saa dog
tilnærmelsesvis, ogsaa hos meget unge Exemplarer af flere Arter,
henhørende til Familien Asteropectinidæ. Ligesaa findes hos
flere Arter af denne Familie, især i den yngre Alder, en
ganske liden, konisk Fremstaaenhed paa Skivens Centrum;
men ved at sammenstille saadanne yngre Dyr af omtrent
samme Størrelse som llyaster have vi fundet, at dennes
Eiendommeligheder ere af en saadan Beskaffenhed, at de
neppe i nogen væsentlig Grad skulle kunne forandres ved
Alderen, og derfor have vi fundet det nødvendigt
midlertidigt at danne en ny Slægt for den.
I levende Live bærer llyaster det centrale
Rygappen-dix saagodtsom opret, men det bevægede sig ved smaa
Bøininger og havde et Udseende, som om det kunde være
en afreven Stilk, hvorved Dyret havde været fæstet. Er
det virkelig Rest af en saadan Stilk, har denne efter
Dyrets Frigjørelse undergaaet nogen Forandring; thi ved at
undersøge den fri Ende af Appendixet, viste denne sig at
være lidt afrundet og næsten overalt besat med de før
beskrevne Pigge.
Ved den første, overfladiske Undersøgelse opstod der
Tanke om, at llyaster muligens kunde?være et ungt
Exemplar af Bathybiaster pallidus, med hvilken den i flere
Punkter har noget tilfælles, men snart maatte denne Tanke
opgives ved at sammenligne unge Exemplarer af
Bathybi-aster med llyaster. Denne har ingen Pedicellarier, og der
hvor Bathybiaster langs Bugfuren har de store,
eiendommelige Pedicellarier, har llyaster en meget stor Pig.
llyaster har 4 stærkp Tænder, imedens unge Exemplarer af
Bathybiader mangle Tænder, og de udvoxne Dyr kun have
to. Og endelig det høist mærkelige, centrale Rygappendix,
der ganske savnes hos Bathybiaster.
Vi omtalte tidligere, at der hos flere Arter
henhørende til Familien Asteropectinidæ fandtes saavel hos yngre
som ældre Dyr en ganske liden, konisk Fremstaaenhed paa
Midten af Skivens Rvgside; men undersøger man denne
Fremstaaenhed, vil man altid finde, at den har samme
Paxillarbeklædning som -hele den øvrige Del af Skivens
Ryg; noget anderledes er det med Rygappendixet hos
llyaster. Beklædningen er her forskjellig fra Skivens, saa at,
om man end kunde være tilbøielig til i morphologisk
Henseende at betragte Rygappendixet som en høiere Udvikling
af den ovennævnte lille, koniske Knop, har det dog
under alle Omstændigheder undergaaet Forandringer, der
giver llyaster et fra alle andre hidtil kjendte Søstjerner
forskjelligt Udseende. Men vi ere tilbøielige til at antage,
at den oftere omtalte lille, central-dorsale Fremstaaenhed
hos Asteropectiniderne er en Levning af en fordums Stilk,
hvorved Dyret har været fæstet, — en Antagelse, der i
høi Grad vinder i Styrke, efter at man er bleven bekjendt
med Rygappendixet hos llyaster, hvilket unægtelig peger
hen paa Embryonalstadiet hos Crinoiderne. Det
forekommer os saaledes meget sandsynligt, at vor llyaster har havt
et saadant -Larvestadium, og at den selv frigjort altid vil
komme til at bære kjendelige Spor efter dette sit tidligste
Ungdomsliv. Men forholder dette sig saa, da have vi for-
the tip of the rays are also met with, if not of the same
size, still approximately so, in very young specimens of
several species pertaining to the family of Asteropectinidæ.
There is also found in several species of that family,
especially in the younger specimens, a quite small, conical
protuberance, in the centre of the disk, but, on a
comparison of such young animals, of about the same dinfensions
as llyaster, we have found, that its peculiarities are of
such a character, that they can, scarcely, in any material
degree, be changed by age, and we have, therefore, found
it necessary, meantime., to form a new genus for it.
During life, llyaster carries its central dorsal
appendix, almost erect, but it moves in small wavings, and
has an appearance as if it were a detached peduncle, by
which the animal had been secured. If it really is the
remnant of such a peduncle, it must, subsequent to the
detachment of the animal, have undergone some change,
because, on examining the free extremity of the appendix, it
is seen to be slightly rounded, and nearly everywhere,
beset with the spines previously described.
On the first superficial examination, the thought
occurred, that Ilyuster might, perhaps, be a young specimen
of Bathybiaster pallidus, which in several features it
resembles, but that thought was speedily abandonned, when
we had compared young specimens of Bathybiaster, with
Tlyaster. The latter has no pedicellariæ, and in the
situation along the ventral furrow, where Bathybiaster has the
long characteristic pedicellariæ, llyaster has a very large
spine, llyaster has four strong teeth, whilst young
specimens of Bathybiaster have no teeth, and the full grown
animal has only two teeth. Finally, we have the highly
remarkable dorsal appendix, which is completely awanting
in Bathybiaster.
We stated previously, that in several species
pertaining to the family of Asteropectinidæ there was found, both
in the young, as well as in the old animals, a quite small,
conical protuberance in the middle of the abactinal disk,
but, when the protuberance is examined, it is always found
to have the same paxillar clothing, as all the rest of
the abactinal disk, but this is not the case with the
appendix of llyaster. The covering, here, is different from
that of the disk, so that, even, if we were disposed to
consider the appendix from a morphological point of view,
as a higher development of the above named small conical
knob; it must still, in every case, have undergone changes
which gives llyaster a different appearance from all other
starfishes hitherto known. But we are disposed to assume,
that the frequently mentioned, small, central dorsal
protuberance in Asteropectinidæ, is a remnant of a former
peduncle by which the animal has been secured, an
assumption which is greatly strengthened after becoming acquainted
with the dorsal appendix in llyaster, which, undoubledly,
points towards the embryonal stage in Crinoidea. It
appears to us, therefore, most probable, that our Tlyaster has
passed such a larva-stage, and that, even when detached,
it will always afterwards bear recognisable trace of its
earliest embryo period. If this is the case, we are, presum-
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