Echinoderms from Southern New Zealand
Fam. Astropectinidae — Psilaster Sladen, 1885
Psilaster acuminates (Sladen, 1889)
- Ten miles south of Cape Campbell, 50 fathoms, March, 1947; coll. F. Abernethy; 377 specimens.
The above record is notable for the evidence it provides of the abundance of the species on at least one portion of the New Zealand continental shelf. It has hitherto been regarded as a somewhat rare, mainly deep-sea form (ranging down to more than 900 fathoms). It was taken by H.M.S. Challenger in the Tasman Sea, and has since been proved to have a wide southern distribution, though the individual records of its having been found total only six occasions. These indicate its presence off South Africa, off South and Eastern Australia, and on the New Zealand shelf. In addition to the above record, one other unrecorded instance is known to me—a specimen taken off Napier, said to have been in deep water (a statement which probably means no more than in the sublittoral zone); it is now in the Napier Museum.
In the large sample studied, only a single six-rayed specimen was discovered—a fact indicating unusually high stability of pentamerism for an asteroid. The colour of both the paxillar area and of the marginal plates is salmon-pink. As it occurs in company with the following larger species, it resembles superficially the younger stages of the latter; in Psilaster, however, only the infero-marginals bear spines, whereas in Persephonaster both series of marginals are so provided. P. acuminatus proves to be an excellent species for dissection by university classes, and has been so employed both at Victoria University College and at the University of Otago. It is notable for the very large size of its polian vesicles, structures which students commonly fail to discover in species more usually studied.
Persephonaster Alcock, 1891
Persephonaster neozelanicus Mrtsn., 1925
- Ten miles south of Cape Campbell, 50 fathoms, mud, March, 1947; coll. F. Abernethy; 70 specimens.
There were no meristic variants in the population-sample studied. The largest individual measures: R, 140 mm.; r, 35 mm.; R/r, 4. The number of marginals to the interbrachial semi-arc is 49 in the same specimen. The species thus reaches a larger size than was hitherto supposed. Mortensen (1925), in describing the type material, stated that there was no anus observable in his specimen. In the present material, the anus is usually placed on a prominence in the centre of the page 7 disc—some specimens have the rectal and pyloric portions of the intestine everted through it. Other new points that may be noted are: the sexes are separate; the gonopores open on the aboral inter-radii, near the margin. The colour in life is striking—the paxillar area salmon-pink, the marginals and underside cream.