126 THE ECHINODERMS OF TORRES STRAIT. 
It reaches Kagoshima Gulf, Japan, on the north, and extends southward on the Australian 
coast to Sharks Bay on the west and Port Molle on the east. Full-grown adults are 25 to 
30 mm. across the disk with arms 5 to 7.5 times as much; a very typical specimen 25 mm. 
across the disk has arms 195 mm. long. The coloration is ordinarily variegated with dark 
and light shades; the colors are rarely clear enough to be called black and white, but are 
commonly dark gray or brown and dirty whitish, dull yellow, or pale brown. In young 
specimens, however, the colors are clearer and the upper arm-spines may have a rosy tint 
which is sometimes very distinct in life (pl. 13, fig. 9), but is entirely lost in preserved 
material. Large specimens with uniformly dark disks (nearly or quite black) and with 
the arms sometimes correspondingly dark are by no means rare, but in all such cases the 
oral shields and the under arm-plates, at least the basal ones, are light, with or without 
darker markings. 
At Mer scolopendrina is very common, but it occupies a restricted and peculiar habitat 
near high-water mark, where the bottom is composed of a furrowed and creviced rock, the 
slightly sloping surface of which is relatively free from sand and from both animal and 
plant life. During the period of low water there is little indication of anything living in 
this region, but as the tide comes in and the water washes over the surface, one sees slender 
processes projecting everywhere out of the rock crevices, and as the water becomes 2 or 3 
inches deep the whole surface is alive with these swaying projections. Examination shows 
them to be the arms of Ophiocomas, all of the same species and all extending further out 
from the rock as the water increases in depth. Further examination shows that these 
arms are in groups of three, the body and the other two arms of each brittle-star remain- 
ing firmly anchored in the crevice. It is not clear whether the actions are associated with 
feeding or not, but it does seem indisputable that they are associated with respiration, the 
tentacles on the swaying arms being very fully distended. With the fall of the tide, the 
brittle-stars retract all the arms into the crevice, and it is astonishing into how small a 
space an individual 20 mm. across the disk can pack its five arms, each 140 to 150 mm. 
long. It was a difficult matter to collect specimens which were actually in the unbroken 
rock, but occasionally large fragments were broken off and lay on the rock surface 
undisturbed by the ordinary tidal movements. Under these fragments numbers of 
Ophiocomas were to be found, and these were usually O. scolopendrina. It was not 
uncommon to find brevipes var. variegata in such a situation, but I never saw that species 
show the reaction to the incoming tide so characteristic of scolopendrina. Further out 
on the reef-flat only very young specimens of scolopendrina were found, and these were 
quite uncommon. 
The complete separation of habitat between scolopendrina and erinaceus (see p. 127), 
their quite unlike habits, and the perfectly distinct coloration, satisfy me that at Mer 
they represent two well-differentiated species. None of the Murray Island scolopendrinas 
have a uniform color, and all of them have relatively long arms, so that there is no evident 
intergradation with erinaceus. Of course, very young specimens, 8 mm. and less across 
the disk, have not the specific characters well marked and hence can not be certainly 
identified. Most of these occurred in the habitat of erinaceus, and hence all may be of 
that species, but I am inclined. to think that when the larve of scolopendrina first settle 
down and undergo their metamorphosis they do so in the corals where erinaceus lives, 
and only as they mature do they pass shoreward to the crevices which the adults inhabit. 
On the other hand, it is possible that just as echinata and riisei, in the West Indies, have 
breeding-periods two months or more apart, so scolopendrina and erinaceus at Mer are 
physiologically isolated from each other, and if that is the case all the young Ophiocomas 
we found are probably erinaceus. 
