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14
Hudskelet af Stichaster albulus og Fig. 16, Tab VI, et
lignende af Stichaster rosens.
Hudskelettet hos Slægten Asterias dannes, som
tidligere berørt, af større og mindre Kalkstykker, der ogsaa
kan siges at være taglagte, rigtignok paa en anden Maade,
idet de korte, smale Kalkstykker lægge sig med deres
afstumpede Ender paa hverandre og danne længere
Tver-bjelker, der ved at støde til de store, regelmæssigt formede
og i Længderækker taglagte Kalkplader danne store Masker,
hvori flere Tentakelrør optages, se Fig. 10, Tab. IV.
Sammenligner man Ryggens Hudskelet hos Asterias
rubens med det hos Stichaster- roseus, saa vil man finde,
at Kalkstykkerne ere tildels forskjellige i Form; men
væsentligst forskjellige ere de i deres Anordning. Hos
Asterias rubens danne de meget vide Masker, der optage flere
Tentakelrør, imedens de hos Stichaster ere meget tæt
taglagte, hvorved Maskerne blive yderst smaa og give Plads
kun for 1, høist 2 Tentakelrør. Hos Asterias rubens
bærer hver Kalkplade paa Rygsiden i Regelen kun 1 Pig;
hos Stichaster roseus er der flere Pigge.
Efter dette skulde man tro, at Slægten Stichaster var
forsaavidt vel begrundet, som man vil lade Hudskelettet
være afgjørende for en Slægts Dannelse. Men nu kommer
Overgangsformerne, hvortil vi maa henregne Asterias
spitsberg ensis og hyperborea samt Asteracanthion albulus, og da
udfyldes Kløften mellem Slægterne Asterias og Stichaster
temmelig betydeligt, saa at der opstaar Tvivl om, til
hvilken Slægt de nævnte Arter skulle henføres.
PI. Vni, fig. 15, dermal skeleton of Stichaster albulns and
PI. VIII, fig. 16, dermal skele ton of Stichaster roseus, will
serve for comparison.
The dermal skeleton in the genus Asterias is formed,
as previously stated, of larger and smaller calcareous
ossicles, which may also be said to be imbricate, although in
another manner, in as much as, that the short narrow
calcareous ossicles lie on each other with their truncated
extremities, and form longer transverse ribs, which by
uniting with the large, imbricate calcareous plates arranged
in regular longitudinal series, produce large meshes, in which
several tentacular tubes are visible, vide Pl. IV, fig. 10.
If we compare the abactinal dermal skeleton in
Asterias rubens with that of Stichaster roseus, we find that the
calcareous ossicles differ, partially, in form, but still more
particularly, in arrangement. In Asterias rubens, they form
very wide meshes which include several tentacular tubes,
whilst in Stichaster, they are very closely imbricate,
produce extremely small meshes, providing space for 1, or at
most 2 tentacular tubes. In Asterias rubens, each
calcareous plate carries, as a rule, only 1 spine on its dorsal
surface, whilst in Stichaster roseus, it carries several spines.
From this we may gather that the genus Stichaster,
was, in so far, well substantiated, if we assume the
dermal skeleton to be the decisive feature in the formation
of a genus. But, now come the transition-forms, to which
we must assign Asterias spitsbergensis and Asterias
hyperborea, as well as Asteracanthion albulus, and then the gap
between the genera Asterias and Stichaster is so much
reduced, that there arises a doubt as to which genus, the
species named ought to be assigned.
Asterias stellionura, Edm. Perrier.
Tab. IV, Fig. 1—9.
Asteracanthion steUionvra, Valene. Coll. Mus. manuscrit.
1869. Asteracanthion stellionura, Ed. Perrier. Recherches
sur les Pédicellaires, pag. 240, pl. 17, fig. 10, a,
b, c, d. Annales des sciences naturelles 5" Sér.
Tome XII.
1875. Asterias stellionura, Ed. Perrier. Archives de
Zoo-logie expérimentale et générale. Tome 4, pag. 310.
1878. Asterias stellionura, Verrill. Marine Fauna of North
America, American Journal of Science and Arts,
3rd Series, Vol. XVI, pag. 214.
Søstjernens Diameter 260""". Skiven er liden, omtrent
30mm i Grjennemsnit, kun lidet hvælvet. De 5 Arme ere
fra 110—120""" i Længde, temmelig flade; 18*"m ved Grun-
Asterias stellionura, Edm. Perrier.
Pl. IV, fig. 1—9.
Asteracanthion stellionura, Valene. Coll. Mus. manuscrit.
1869. Asteracanthion stellionura, Ed. Perrier. Recherches
sur les Pédicellaires, pag. 420, Pl. 17, fig. 10, a,
b, c. d. Annales des sciences naturelles 5" Sér.
Tome XII.
1875. Asterias stellionura. Ed. Perrier. Archives de
Zoo-logie, expérimentale et générale. Tome 4, pag. 310.
1878. Asterias stellionura. Verrill. Marine Fauna of
North America, American Journal of Science and
Arts 3r" Series, Vol. XVI, pag. 214. •
The diameter of this starfish is 260""". The disk is
but small, being only about 30""" in "diameter, and it is
only slightly convex. The five rays are rather flat; they
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