1861. Psohts phantapus, Sars, Ovexsigb af Norges Eohinodermer, p. 112.
1867. Psolus phantapus, Selenka, Zeitsoh. f. wiss. Zool. Bd. xvii. p. 342.
1868. Psolusphantapus, Semper, Reisen im Archipel der Philippinen, Holothurien, pp. 6 2 ,2 7 2 .
The Key. A. M. Norman, by whom the Echinodermata of the ‘Valorous’ Expedition
were determined *, has kindly informed us that specimens of this Holothuroid
were taken at Holsteinborg and Godhavn. The writers, not having had the opportunity
of examining any Arctic examples of this well-known form, content themselves
with simple reference to the principal literature and distribution of the species.
Distribution.
a. Greenland: Godhavn, lat. 69° 14' (‘Valorous' Exped.), the most northern
locality on record; Holsteinborg Harbour (‘ Valorous ’ Exped.); Fiskernsesset (Lütken);
Arksut (Barrett).
b. North o f American Continent: Grand Manan, at low water and in 40 fmS.
(Verrill); Maine (Stimpson).
c. North o f European Continent: Iceland, Faeroe Islands, Finmark, Scandinavian
coasts, British Isles.
Psolus Fabricii (D. & K .\ Lütken. Plate I, Figs. 9-13.
1780. Holothuria sguamata, Fabricius, Fauna Groenlandica, p. 356. no. 348 (non 0 . F . M., nec D. & K.). -
1841. Holothuria sguamata, Gould, Invert. Anim. Massachusetts, p. 345.
1844. Guvieria Fabricii, Düben & Koren, Kongl. Yet.-Akad. Handl. 1844, p. 316.
1851. Guvieria Fabricii, Ayres, Proceed. Boston Soc. Nat. Histrvol. iv. pp. 35-37.
1853. Guvieria Fabricii, Stimpson, Syn. Mar. Invert. Grand Manan, p. 16.
1857. Psolus Fabricii, Lütken, Vid. Meddel. N. Forening i Kjöbenhavn, 1857, p. 13.
1866. Lophothuria Fabricii, Yerrill, Proceed. Boston Soc. N at. H ist. vol. x . p. 354.
1867. Guvieria Fabricii, Selenka, Zeitschr. f. wiss. Zool. Bd. xvii. p. 343.
1868. Psolus Fabricii, Semper, Reisen im Archipel der Philippinen, Holothurien, pp. 62,272.
1877. Psolus Fabricii, Marenzeller, Ccelent. Echin. u. Würmer d. öst.-ung. Nordpol.-Exped. p. 32
(Denksch. d. k. Akad. d. Wissensch. Wien, Bd. xxxv.).
Body somewhat limpet- or chiton-shaped, arched above and flat beneath ; dorsal
and ventral surfaces separated by a perfectly sharp angle, the contour of the periphery
being oval. Both oral and anal apertures are situated upon the dorsal area, one at
either extremity, and rather nearer to the margin than midway from the centre in the
longitudinal axis of the body. The dorsal surface is covered with very large plate-like
scales, which imbricate upon one another, their free margins being round in contour
and directed centripetally; those in the neighbourhood of the apertures are somewhat
smaller, and are grouped round the opening itself as the centre of their arrangement,
whilst a number of the scales that immediately surround the orifice become developed
into thick calcareous wart-like tubercles. Bordering the extreme outer edge of the
dorsal area are about two rows of very much smaller scales, not more than one tenth
* I n the “ Preliminary Report of the Biological Results of a Cruise in H.M.S. ‘ Yalorous ’ to Davis Strait
in 1875,’* Proceed. Roy. Soc. vol. xxv. pp. 202-215.
the size of the others. The scales are densely covered with very large granules, but
which in old specimens are not unfrequently abraded in places.
The integument of the ventral area, although thin, is tough and leathery, and
presents no asperities to the touch. The ambulacral feet are entirely confined to the
ventral area, and are limited to its extreme outer margin, round which the suckers
form a broad border about four or five rows deep, very closely crowded, and having
no perceptible order in their arrangement except in the outermost series, which are
smaller than the rest, and form a line parallel with the margin. At the anterior and
posterior ends of this oval marginal series may be found a few additional suckers
extending along the median line: these are the rudiments of the aborted middle
ambulacral series; and it is rare that more than four or five rows of four suckers each
are present.
The mouth-ring resembles that of P. squamatus, D. & K., the elements having
more or less the form of an inverted Y, and the five interradial pieces being smaller
than the radials.
The Polian vesicle is large and single, the generative tubes extremely numerous
and extensive, and the muscular system much more strongly developed than m
P. squamatus (Liitken),
Kespecting the spicules which occur in the cuticle of this Holothuroid, those of
the ventral skin are indefinite in shape, and are more correctly described as calcareous
reticulations having large circular apertures than as plates punctured with holes.
Short prolongations frequently rise at right angles from the decussations or midway on
the intercalary portions; and occasionally secondary branchings are formed from these.
Here and there small cup-shaped spicules are to he met with, probably undeveloped
stages of the larger spicules. The tubes of the sucker-feet are overlaid with spicules
somewhat similar in shape and character to those of the ventral cuticle; and the
extremity is provided with a large circular calcareous disk, likewise of reticulated
structure, with the holes very large, close together, and nearly equal in size.
Colour and Size.—Psolus Fabricii is, when alive, of a dark red colour, which
in spirit becomes changed to brown. Ayres speaks of his American specimens as
being of a bright brick-red when alive {loo. cit. p. 36). One of the largest examples
measured 3 J inches in length and over 2 inches in breadth {Liitken).
Premature Form.—In a young state the dorsal surface is more depressed, and the
orifices of the alimentary canal are somewhat nearer the margin than in the adult
animal. The ambulacral feet are limited to a double row of suckers surrounding the
margin of the ventral area; and no trace is visible of the median series. I t is of
interest to note that at this stage the young of the present species are almost undis-
tinguishable from those of Ps. phantapus of a corresponding period of growth, although
the latter is a form whose habit differs most strikingly from that of the present species
when adult examples are compared. The same remark holds good for the young stages
of Ps. squamatus as well, the superficial differences at an early phase being nothing
more than slight variations in the character of the spicules that indurate the ventral
cuticle.
c 2