A Starfish of rather depressed form, having five broad flat arms; the proportion
of the greater to the lesser radius being about 3 :1 approximately. The calcareous
skeleton of the abactinal surface forms a very regular network, and the large conspicuous
paxilke that spring from the intersections form longitudinal series which run
parallel to the median line of the ray; consequently only two or three of the middle
rows reach to the tip, although from fourteen to sixteen may be counted at the base of
the arm. The paxillae, which are very compact, have a remarkably large stout pedicle
nearly twice as wide as high, and bear a crown of spinelets, numbering from fifteen
to twenty, or even more in large specimens, in length about equal to the diameter
of the base. The spinelets are flat in young examples, and from the angles of
their apex, which is as broad or broader than the base, proceed two small denticles,
giving to the spinelet the appearance of a two-pronged fork; with increasing age,
however, the spinelets become multilaminate, and the number of apical denticles
oorresponds with that of the laminse, which radiate from the median axis of the
spinelet.
The papula are in groups of from four to ten or twelve in number, varying according
to age and size. They are most numerous upon the disk, the interspaces between the
ossicles of the calcareous network being smaller further out upon the rays, where the
papulae are consequently fewer and the paxillae closer together.
The sides of the rays are deep and perpendicular, and are bounded by a dorsal and
a ventral series of marginal paxillae ; they stand wide apart from one another, and are
about twenty (17-22). in number from the arm-angle to the extremity of the ray. The
paxillae of the dorso-lateral series are larger than the general paxillae of the dorsal area,
and are directed somewhat upwards. The ventro-lateral series, which are much larger
and very prominent, alternate with these, standing opposite to the interspaces, and are
directed at an angle downwards; their pedicles are nearly twice as broad as the foregoing
and oval in section, whilst the spinelets attached to them are somewhat shorter
than those on the dorsal paxillae. There are no paxillae in the space between the
dorsal and ventral series above named, the sides of the rays being bare.
Each adambulacral plate bears two series of spinelets: one which runs parallel to the
furrow, and is composed of three to five equal-sized spinelets; and a transverse series of
three or four placed obliquely or even at right angles to the furrow-series, a thick
membrane uniting the spinelets and forming a webbed comb.
The ventral interbrachial areas are large, and bear a number of paxillae arranged
in rows parallel with the furrow, two, three, or sometimes even more of such rows
being present. In the largest example we have examined the innermost row has
eleven or twelve paxillae extending from the median interbrachial line out along the
ray; the next outermost numbers 5, the third 3, the angle thus left being filled up by
a solitary paxilla. The paxillse are large and all covered with a thick membrane; their
bases or pedicles are very short, and carry six to eight spinelets arranged somewhat like
a double fan, all radiating and directed outwards. The main group of paxillse which
stand upon the area are nearly equal in size, but the five or six most aboral ones of the
innermost row diminish in size as they recede from the mouth; they do not extend
beyond one third of the length of the ray, and the most outward ones are made up of
only three or four small spinelets, not sufficient to form a paxilla proper.
The mouth-plates are large and broad, and the marginal spines interlock with those
of the neighbouring mouth-angle.
The madreporiform tubercle is small and often difficult to find, being almost hidden
by paxillse; it is situated a little nearer to the centre than midway between that point
and the arm-angle, and in some specimens it stands at about one third the distance.
Size.—The greater radius of the three specimens known to Diiben and Koren
measured respectively 30, 16-18, and 11 millims.; the specimens from Cape Frazer
are somewhat larger than this, whilst those from Discovery Bay measure 82 and 53
millims. in their greater radius. The largest of the Cape-Frazer specimens is about
32 millims. in the greater radius, 65 millims. in its greatest diameter, and 21 millims.
across the disk, the arms at their base being 13 millims. broad.
Colour.—According to Diiben and Koren, the colour of the living animal is brick-
red above and white beneath; the eye-spots bright red.
Habitat.—Although no actual record has been preserved of the nature of the
ground inhabited by this Starfish in the far north, a certain amount of incidental
evidence is furnished by the fact that the smaller of the two specimens from Discovery
Bay has its stomach filled with the remains of Antedon, and upon which it had
evidently taken its last meal! In all probability they were fellow residents on the
same sea-bed.
Variations.—Under this head should be recorded a specimen obtained by Mr. Hart
in Discovery Bay during the British Arctic Expedition of 1875-76, and which we have
included within the present species only after much hesitation. The greater radius of
this example measures 82 millims., the lesser 30 millims. The arm-angles are much
more rounded, and the rays comparatively much broader at the base and more rapidly
tapering (being remarkably attenuated towards the extremity) than in smaller forms
with which we have previously been acquainted. By this means an extremely broad
character is imparted to the disk, and a contour altogether different from that given by
Diiben and Koren and by Sir Wyville Thomson in figures of Solaster furcifer. The
present specimen is also noteworthy from the great number of papulae that are present;
in fact so numerous are they, that the dorsal paxillae have the appearance of
springing from quite a forest of these tubelets, whilst the degree to which every
appendage of the body is invested with membrane, and all the ventral spinelets webbed
together, tends to produce a character which, although superficial, is remarkably
striking and conspicuous.
At first sight it would seem that these modifications should be considered marks of
specific distinction; and such 'per se the writers would have been disposed to regard them,
had not a second (and smaller) specimen, likewise obtained in Discovery Bay, furnished
a phase of gradation between this apparently independent form and examples of the same
species dredged off Cape Frazer by Capt. Feilden—the larger of these latter presenting
a stage which diverges from the ordinary form (as diagnosed by Diiben and Koren) in
the direction of the above-named specimen.