Chætodon setifer, _Bloch_, Ichth. pl. 425. fig. 1.
———— _Cuv. et Val._ Hist. des Poiss. tom. vii. p. 58.
FORM.—This species is one of those characterized by a prolongation of
a portion of the soft dorsal fin. In the present specimen it is the
sixth soft ray which is thus prolonged. The total length of this
ray, measured from the root, is half the entire length of the fish;
and that portion of it which exceeds the adjoining rays is rather
more than half. Although the preopercle can hardly be called
denticulated, yet there are some faint traces of rudimentary
denticulations at the lower angle. The general form, in all other
respects, agrees with the descriptions of Cuvier and other authors.
D. 13/24; A. 3/21; C. 17, and 6 short; P. 16, the first short; V. 1/5.
Length 6 inc. 3 lines.
COLOUR.—“Body pale, with narrow dark straight lines which form
network: across the eye a black band: posterior half of the body
bright orange: upper part of the prolongation of the dorsal fin
edged with black, and a round patch of the same.”—D. The black
ocellus extends from the fifth to the thirteenth ray of the soft
dorsal. There is no trace of the four red or yellow streaks said by
Cuvier and Valenciennes to cross the forehead from eye to eye; but
probably they are effaced by the action of the spirit.
_A second specimen_ only differs from the above in being smaller,
measuring in length not quite five inches; in having the fifth
(instead of sixth) ray in the soft dorsal prolonged; and in the
ocellus extending from the fifth to the tenth ray only. In the last
two respects it agrees better with the description in the ‘Histoire
des Poissons.’ The filamentous ray terminates in an extremely fine
hair, which leads me to think that the extreme portion of this ray
in the first specimen has been broken off.
Habitat, Keeling Island, Indian Ocean.
Mr. Darwin’s collection contains two individuals of this species
procured on coral reefs at the Keeling Islands. As according to his
notes made from the recent fish, the posterior half of the body is
bright orange, Bloch’s figure may not be so much overcoloured as is
supposed by Cuvier and Valenciennes, who state that he has represented
of a bright red, what ought to be silvery grey and yellow ochre. Perhaps
the colours may depend in some measure on the season. Mr. Darwin’s
specimens were obtained in the month of April.