“Ophiacantha vivipara, var. pentactis, n.var.
(PlateVII, figs. 3,4)
St. 170. 23. ii. 27. Off Cape Bowles, Clarence Island, 342 m. 3 specimens.
St. 187. 18. iii. 27. Neumayr Channel, Palmer Archipelago, 259-354 m. 5 specimens.
St. 190. 24. iii. 27. Bismarck Strait, Palmer Archipelago, 93-130 m. 3 specimens.
St. 599. 17. i. 31. 67° 08' S, 69° 06' W, 203 m. 1 specimen.
In his work on the Echinoderms of the IIe Expédition Antarctique Française ('Pourquoi-Pas?') Koehler has figured (pl. xi, i) a large five-armed specimen under the name of O. vivipara; he regards this five-armed form as simply identical with the normally 6-7-armed O. vivipara. Particularly he emphasizes the fact that there are all possible transitions between the forms with the disk covered by a uniform granulation and those with numerous spines on the disk. Although these 5-armed specimens generally have more numerous spines on the disk besides the granules, there is thus no reason for distinguishing them from the typical 6-7-armed O. vivipara ; and also in the other characters they agree, on the whole, with the typical vivipara. Still the matter is not
quite so simple.
It is undeniable that these 5-armed specimens in general have a much more robust
appearance than vivipara (cf. Plate VII, figs. 2-4); also the arms are longer and more
robust. This can hardly be due simply to the fact that they have fewer arms than the
typical form. Then it is a very noticeable fact that this large 5-rayed form is not met with
among the specimens from the neighbourhood of the Falkland Islands, but only very
far south, from the Palmer Archipelago to the Graham Land region. (Koehler's 5-rayed
specimens are also all from this southern region.) If it were simply an individual variation
of the 6-7-rayed vivipara, it would be hard to understand why such forms
should not occur equally commonly also in the Falkland region (the single 5-rayed
specimen I have seen from there is only a very young one). The typical vivipara also
occurs in the more southern region, together with the 5-rayed form; but whereas the
5-rayed form is of common occurrence in the south, it apparently does not occur farther
north. Further, there are among these large 5-rayed specimens several males, whereas no male specimens were observed among the typical 6-7-rayed specimens. None of the
female specimens of the 5-rayed form have young ones in the bursae, so it is quite
possible that this form is not viviparous — at least there is no proof that it is viviparous.
Thus, in my opinion, it is not justifiable simply to identify these specimens with the
typical 6-7-rayed O. vivipara. If it is really non-viviparous, it must represent a separate
species, but so long as we do not know this for certain, and in view of its resemblance
with vivipara in general structure, I think it the safest course for the present to designate
it as a variety of O. vivipara.
From O. rosea, with which there is much general resemblance, it is distinguished
particularly by the outer mouth papillae being simple, not forming a cluster at the outer
mouth tube foot. From O. densispina it diflfers in having both granules and spines on
the disk, and in the arm spines being more smooth and not joining in the dorsal median
line. Also the shape of the mouth shields is somewhat different (Figs. 5-6).
(Mortensen, 1936; 248-249)
